Internet DRAFT - draft-seantek-certspec
draft-seantek-certspec
Network Working Group S. Leonard
Internet-Draft Penango, Inc.
Intended status: Standards Track March 13, 2017
Expires: September 14, 2017
Textual Specification for Certificates and Attributes
draft-seantek-certspec-11
Abstract
Digital certificates are used in many systems and protocols to
identify and authenticate parties. This document describes a string
format that identifies certificates, along with optional attributes.
This string format has been engineered to work without re-encoding in
a variety of protocol slots.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 14, 2017.
Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
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described in the Simplified BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
1.2. Definitions . . . . . . . . . . . . . . . . . . . . . . . 3
2. Motivation and Purpose . . . . . . . . . . . . . . . . . . . 4
2.1. Static Identification . . . . . . . . . . . . . . . . . . 4
2.2. Relationship with Other Specifications . . . . . . . . . 5
3. Basic Syntax and ABNF . . . . . . . . . . . . . . . . . . . . 5
4. certstring Syntax . . . . . . . . . . . . . . . . . . . . . . 5
5. certspec Syntax . . . . . . . . . . . . . . . . . . . . . . . 6
5.1. certspec Type and Value . . . . . . . . . . . . . . . . . 8
6. Standard Certificate Specifications . . . . . . . . . . . . . 8
6.1. Cryptographic Hash-Based Specifications . . . . . . . . . 8
6.2. Content-Based Specifications . . . . . . . . . . . . . . 9
6.3. Element-Based Specifications . . . . . . . . . . . . . . 10
6.4. Path-Based Specifications . . . . . . . . . . . . . . . . 11
6.5. Algorithm for Distinguishing ASN.1 PDUs . . . . . . . . . 14
7. Other Certificate Specifications . . . . . . . . . . . . . . 16
7.1. DBKEY (Reserved) . . . . . . . . . . . . . . . . . . . . 16
7.2. SELECT (Reserved) . . . . . . . . . . . . . . . . . . . . 16
8. Multiple certspecs (multispec) . . . . . . . . . . . . . . . 16
9. Attributes (pkcsattrs) . . . . . . . . . . . . . . . . . . . 17
9.1. ABNF . . . . . . . . . . . . . . . . . . . . . . . . . . 19
9.2. Mandatory Attribute Support . . . . . . . . . . . . . . . 20
9.3. Canonicalization . . . . . . . . . . . . . . . . . . . . 21
10. Whitespace . . . . . . . . . . . . . . . . . . . . . . . . . 21
11. Guidelines for Extending certspec . . . . . . . . . . . . . . 22
12. Use of certspec in Systems . . . . . . . . . . . . . . . . . 23
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24
14. Security Considerations . . . . . . . . . . . . . . . . . . . 25
15. References . . . . . . . . . . . . . . . . . . . . . . . . . 26
15.1. Normative References . . . . . . . . . . . . . . . . . . 26
15.2. Informative References . . . . . . . . . . . . . . . . . 27
Appendix A. Mandatory Attribute Descriptors for Distinguished
Names . . . . . . . . . . . . . . . . . . . . . . . 29
Appendix B. Recommended Attribute Descriptors for issuersn
certspec . . . . . . . . . . . . . . . . . . . . . . 30
Appendix C. Suggested Algorithm for Distinguishing Textual Data 30
Appendix D. Binary Formats for Conveying Certificates with
Attributes . . . . . . . . . . . . . . . . . . . . . 31
D.1. PKCS #12 certs-only Profile . . . . . . . . . . . . . . . 31
D.2. CMS SafeContents contentType . . . . . . . . . . . . . . 33
D.3. SafeContents-to-PKCS#12 BER Adapter . . . . . . . . . . . 33
Appendix E. Textual Encoding of Attributes . . . . . . . . . . . 34
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 35
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1. Introduction
Digital certificates [RFC5280] are used in many systems and protocols
to identify and authenticate parties. Security considerations
frequently require that the certificate must be identified with
certainty, because selecting the wrong certificate will lead to
validation errors (resulting in denial of service), or in improper
credential selection (resulting in unwanted disclosure or
substitution attacks). The goal of this document is to provide a
uniform syntax for identifying certificates with precision and speed
without re-encoding in a variety of protocol slots.
Using this syntax, any protocol or system that refers to a
certificate in a textual format can unambiguously identify that
certificate by value or reference. Implementations that parse these
strings can resolve them into actual certificates. Examples include:
SHA-1:3ea3f070773971539b9dbf1b98c54be3a4f0f3c8
ISSUERSN:cn=AcmeIssuingCompany,st=California,c=US;0134F1
BASE64:MIIBHDCBxaADAgECAgIAmTAJBgcqhkjOPQQBMBAxDjAMBgNVBAMT
BVNtYWxsMB4XDTEzMTEwNTE5MjUzM1oXDTE2MDgwMjE5MjUzM1ow
EDEOMAwGA1UEAxMFU21hbGwwWTATBgcqhkjOPQIBBggqhkjOPQMB
BwNCAAS2kwRQ1thNMBMUq5d/SFdFr1uDidntNjXQrc3D/QpzYWkE
WDsxeY8xcbl2m0TBO4TJ/2CevdoOX0OMIOaqJ/TNoxAwDjAMBgNV
HRMBAf8EAjAAMAkGByqGSM49BAEDRwAwRAIgPyF8ok6h2NxMQ4uJ
OcGcXYcvZ1ua0kB+rIv0omHcfNECICKwpTp3LDIwhlHTQ/DulQDD
eYn+lnYQVc2Gm1WKAuxp
/etc/myserver.cer|friendlyName=fluffy the Tomcat
URI:https://certificates.example.com/acme/BAADF00D.cer
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119.
1.2. Definitions
The term "certificate" means either a certificate containing a public
key [RFC5280] or an attribute certificate [RFC5755]. When a
certificate [RFC5280] alone is to be distinguished, this
specification may use the term "public key certificate".
The term "whitespace" means HT, VT, FF, LF, CR, and SP, when
referring to the ASCII range. An implementation SHOULD also consider
whitespace beyond the ASCII range, if the implementation supports it,
e.g., the characters that have the White_Space character property in
[UNICODE].)
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The term "entity" means a MIME entity [RFC2045], namely, a fixed
sequence of octets (i.e., data) with an Internet media type and
optional parameters.
2. Motivation and Purpose
Although certificates [RFC5280] have diverse applications, there has
been no uniform way to refer to a certificate in text. De-facto
standards such as PEM [RFC1421] and PKIX text encoding [RFC7468] are
used to include whole certificates in textual formats, but this
practice is impractical for a variety of use cases. Certificates
that identify long public keys (e.g., 2048-bit RSA keys) and that
contain required and recommended PKIX extensions can easily exceed
many kilobytes in length.
The purpose of this document is to provide a uniform textual format
for identifying individual certificates, with human usability as a
design goal. Certificate specifications, or "certspecs", are not
designed or intended to provide a search tool or query language to
match multiple certificates. The goal is to replace data elements
that would otherwise have to include whole certificates, or that
employ proprietary reference schemes. For example, certspecs fit
easily into XML/SGML data, YAML, JSON, and config files and databases
(e.g., .properties, .ini, and Windows Registry) with minimal required
escaping.
To be usable by humans, certspecs are supposed to be amenable to
copy-and-paste operations. The structure of a certspec is also
supposed to be plainly visible so that someone glancing at a certspec
can ascertain the data types that it comprises. This specification
addresses the "speed" goal by incorporating identifiers that
implementations typically use as indexes to certificate databases.
For instance, many implementations index certificates by issuer and
serial number, or by SHA-1 hash, regardless of how collision
resistant those pieces of data are at present.
2.1. Static Identification
Identifying a specific certificate by reference or value allows
diverse applications to have a common syntax. For example,
applications can store certspecs as local or shared preferences, so
that users can edit them without resorting to application-specific
storage formats or relying on the availability of particular
protocols represented by URIs (such as http:, ldap: [RFC4516], file:
[RFC1738], or ni: schemes). When conveyed in protocol, a certspec
can identify a specific certificate to a client or server using text-
based formats such as YAML, XML, JSON, and others. The format
described in this document is intended to be readily reproducible by
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users using common certificate processing tools, so that users can
easily create, recognize, compare, and reproduce them at a glance.
For example, the hash-based identifications use hexadecimal encoding
so that a user can easily compose or compare an URN with a simple
copy-and-paste operation.
2.2. Relationship with Other Specifications
Certspecs and their attendant elements are textual strings, and are
intended for use with textual protocols. Where possible, certspecs
are just identifiers from other protocols with minimal syntactic
sugar to distinguish one type of certspec from another. Several
certspec productions look like URIs, but are not. To distinguish
certspec syntax from URI syntax, this Internet-Draft capitalizes the
"introducer characters" of the various certspec types and does not
require that they be delimited with a colon, even though these
productions (mostly) are case-insensitive and (mostly) end with a
colon. OpenSSL's x509v3_config format inspired this aspect of the
syntax.
3. Basic Syntax and ABNF
The bulk of this document defines textual formats for interchange.
While textual strings in this document can be in any character
encoding, the delimiter characters in this document are drawn from
ASCII. Unicode [UNICODE] support at some level (e.g., in attribute
values that are in LDAP string form) is inevitable, but the general
premise is that an implementation can convert the production (or
appropriate parts of the production) to Unicode when it is needed.
The ABNF in this document is normative, and is drawn from [RFC5234],
[RFC7405], [I-D.seantek-abnf-more-core-rules], and
[I-D.seantek-unicode-in-abnf]. The ABNF reuses certain definitions
from [RFC4512] and [RFC4514], but does not formally reference those
rules due to notating Unicode characters beyond the ASCII range in a
more modern way.
4. certstring Syntax
A certificate string ("certstring") is a string with a single
certspec (see Section 5) or multiple certspecs (a "multispec", see
Section 8), followed by an optional set of attributes ("pkcsattrs",
see Section 9). A multispec is a discriminator for a single
certificate. In contrast, pkcsattrs are optional attributes
associated with a single certificate. These attributes do not
participate in selecting a certificate, but might be used to identify
other things, such as the token on which associated private keying
material resides. The string has the ABNF:
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certstring = (certspec / multispec) [ "|" pkcsattrs ]
Figure 1: certstring ABNF
5. certspec Syntax
A certspec is a string that is intended to identify a single
certificate. A certspec has introducer characters followed by value
characters; these introducer characters MAY be part of the "value" of
the identifier. The ABNF is:
certspec = certspec-hash / certspec-content / certspec-el /
certspec-path
certspec-hash = "SHA-1" ":" 40HEXDIG /
"SHA-256" ":" 64HEXDIG /
"SHA-384" ":" 96HEXDIG /
"SHA-512" ":" 128HEXDIG
; Proposal: Hash Function Textual Name registry hereby limited
; to RFC 3986 scheme characters
certspec-content = ("HEX" / "BASE16") ":" 1*(2HEXDIG) /
"BASE64" ":" base64string
base64char = ALPHA / DIGIT / "+" / "/"
base64string = 1*(4base64char)
[ 3base64char "=" / 2base64char "==" ]
; based on [RFC4512][RFC4514]
distinguishedName = [ relativeDistinguishedName
*( "," relativeDistinguishedName ) ]
relativeDistinguishedName = attributeTypeAndValue
*( "+" attributeTypeAndValue )
attributeTypeAndValue = attributeType "=" attributeValue
attributeType = descr / numericoid
num = "0" / %x31-39 *DIGIT
descr = ALPHA *(ALPHA / DIGIT / "-")
numericoid = ("0" / "1" / "2") 1*("." num)
attributeValue = string / hexstring
string = [ ( leadchar / pair ) [ *( stringchar / pair )
( trailchar / pair ) ] ]
; excl SP " # + , ; < > \
leadchar = %x01-1F / %x21 / %x24-2A / %x2D-3A /
%x3D / %x3F-5B / %x5D-7F / BEYONDASCII
; excl SP " + , ; < > \
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trailchar = %x01-1F / %x21 / %x23-2A / %x2D-3A /
%x3D / %x3F-5B / %x5D-7F / BEYONDASCII
; excl " + , ; < > \
stringchar = %x01-21 / %x23-2A / %x2D-3A /
%x3D / %x3F-5B / %x5D-7F / BEYONDASCII
pair = "\" (" " / %x22-23 / %x2B-2C / %x3B-3E / "\" / 2HEXDIG)
hexstring = "#" 2HEXDIG
certspec-el = "ISSUERSN" ":" distinguishedName ";" serialNumber /
"SKI" ":" 1*(2HEXDIG)
serialNumber = 1*(2HEXDIG)
certspec-path = certspec-uri / certspec-file / certspec-reg
; from RFC3986; RFC 6570
; superfluous: URI-reference = URI-reference@[RFC3986]
URI-Template = URI-Template@[RFC6570]
certspec-uri = "URI:" URI-Template
; see POSIX, etc.
certspec-file = ("/" / "\" / [A-Z] ":" /
("." / "..") ("/" / "\") / "~" / "%" / "$")
*filepathchar
; BEYONDASCII is from draft-seantek-more-core-rules
filepathchar = %x01-29 / %x2B-3B / "=" / %x40-5B /
%x5D-7B / %x7D-7F / quoted-fpc / BEYONDASCII
quoted-fpc = "\" ("*" / "<" / ">" / "?" / "\" / "|")
; TODO: validate Windows file path characters
certspec-reg = reg-hive 1*("\" reg-key)
["\\" reg-value-name]
reg-hive = reg-local-hive / reg-remote-hive
reg-local-hive = "HKEY_LOCAL_MACHINE" / "HKEY_CURRENT_USER" /
"HKEY_CLASSES_ROOT" / "HKEY_USERS" /
"HKEY_CURRENT_CONFIG" /
"HKLM:" / "HKCU:" / "HKCR:" /
"HKU:" / "HKCC:"
; TODO: better specify computer name; it could be a NETBIOS name...?
reg-remote-hive = "\\" reg-name@[RFC3986] "\" ("HKLM" / "HKU") ":"
; escape < > |. Need to figure out if 7F is ok, also C0, C1, etc.
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reg-key = 1*(%x20-3B / %x3D / %x3F-5B %x5D-7B / %x7D.7E /
"\<" / "\>" / "\|" / BEYONDASCII)
; reg-value-name can be empty
reg-value-name = *(%x20-3B / %x3D / %x3F-7B / %x7D.7E /
"\<" / "\>" / "\|" / BEYONDASCII)
Figure 2: certspec ABNF
5.1. certspec Type and Value
Semantically, a certspec is comprised of its type and value. The
value is always provided, but the type is either explicitly declared,
or is inferred from the initial (introducer) characters in the type.
When types are explicitly provided, they are compared case-
insensitively. The certspec-value identifies the certificate
specification value.
Several certspecs use hexadecimal encodings of octets. Generally: if
the hex octets are malformed (whether in the source material, such as
the corresponding certificate element, or in the hex text), the
certspec is invalid.
6. Standard Certificate Specifications
Standard certificate specifications are intended for interchange as
user- and developer-friendly identifiers for individual certificates.
This section provides four cryptographic hash-based certspecs, two
content-based certspecs, two element-based certspecs, and three path-
based certspecs.
6.1. Cryptographic Hash-Based Specifications
A cryptographic hash or "fingerprint" of a certificate uniquely
identifies that certificate. For hash-based certspecs, the hash is
computed over the octets of the DER encoding of the certificate,
namely, the Certificate type in Section 4.1 of [RFC5280] and the
AttributeCertificate type in Section 4.1 of [RFC5755]. The certspec-
value is the hexadecimal encoding of the hash value octets. For
example, a 256-bit SHA-256 hash is represented by exactly 32 hex
octets, or 64 hex characters. The hexadecimal encoding is not case
sensitive.
A conforming generator SHALL emit only hexadecimal encoded data,
i.e., the characters A-F (case-insensitive) and 0-9.
A conforming parser SHALL accept value productions that contain the
following non-hex digits: whitespace, hyphen, and colon. A
conforming parser MAY accept values that contain other characters.
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Conforming implementations to this Internet-Draft MUST process these
hash-based certspecs, unless security considerations dictate
otherwise. Acceptable reasons for refusing to process a certspec
include a) the local policy prohibits use of the hash, or b) the hash
has known cryptographic weaknesses, such as a preimage attacks, which
weaken the cryptographic uniqueness guarantees of the hash.
6.1.1. SHA-1
The introducer production is "SHA-1:". The hash is computed using
SHA-1 [SHS].
6.1.2. SHA-256
The introducer production is "SHA-256:". The hash is computed using
SHA-256 [SHS].
6.1.3. SHA-384
The introducer production is "SHA-384:". The hash is computed using
SHA-384 [SHS].
6.1.4. SHA-512
The introducer production is "SHA-512:". The hash is computed using
SHA-512 [SHS].
6.2. Content-Based Specifications
Content-based certspecs identify certificates by their constituent
octets. For small-to-medium certificates, identifying the
certificate by embedding it in the certspec will be computationally
efficient and resistant to denial-of-service attacks (by always being
available). A conforming implementation MUST implement base64 and
hex specs.
The octets of a certificate are the octets of the DER encoding of the
certificate, namely, the Certificate type in Section 4.1 of [RFC5280]
and the AttributeCertificate type in Section 4.1 of [RFC5755]. The
DER encoding includes tag and length octets, so it always starts with
30h (the tag for SEQUENCE) followed by any octet other than 80h (the
marker for indefinite length encoding). See also Section 6.5.
Because users may end up copying and pasting base64 or hex-encoded
certificates into certspecs, and because these certspecs will
routinely exceed 72 characters, a production might contain embedded
whitespace. A conforming generator SHALL emit no whitespace, or
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SHALL emit a hanging indent, between semantically significant
characters.
6.2.1. BASE64
The introducer production is "BASE64:". The value production is the
BASE64 encoding of the certificate octets (Section 4 of [RFC4648]).
6.2.2. HEX and BASE16
The introducer production is "HEX:" or "BASE16:". Generators MUST
generate "HEX:"; parsers MUST accept "HEX:" and "BASE16:". The value
production is the hexadecimal encoding of the certificate octets.
6.3. Element-Based Specifications
A certificate may be identified by certain data elements contained
within it. The following certspecs reflect the traditional reliance
of PKIX [RFC5280] and CMS [RFC5652] on a certificate's issuer
distinguished name and serial number, or a certificate's subject key
identifier.
Note that distinguished names can contain "|" in attribute value
strings, but this production is unambiguous with the pkcsattrs
delimiter because distinguished names are always terminated by ";".
6.3.1. ISSUERSN: Issuer Name and Serial Number
The introducer production is "ISSUERSN:".
6.3.1.1. Issuer
The distinguishedName production encodes the certificate's issuer
distinguished name (DN) field in LDAP string format [RFC4514].
[RFC4514] no longer separates relative distinguished names (RDNs) by
semicolons, as required by its predecessor, [RFC2253]. Accordingly,
";" is used to separate the issuer's DN from the subject's serial
number.
6.3.1.2. Serial Number
The serialNumber production is the hexadecimal encoding the DER-
encoded contents octets of the CertificateSerialNumber (INTEGER,
i.e., not the type or length octets) as specified in Section 4.1.2.2
of [RFC5280].
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6.3.1.3. Conformance
A conforming implementation SHALL implement the ISSUERSN certspec.
An implementation MUST process serial numbers up to the same length
as required by Section 4.1.2.2 of [RFC5280] (20 octets), and MUST
process distinguished name strings as required by [RFC4514],
including the table of minimum AttributeType name strings that MUST
be recognized. Additionally, implementations MUST process attribute
descriptors specified in [RFC5280] (MUST or SHOULD), and [RFC5750]
(specifically: E, email, emailAddress). For reference, a complete
list of required attribute descriptors is provided in Appendix A.
Implementations are encouraged to recognize additional attribute
descriptors where possible. A sample list of such attribute
descriptors is provided in Appendix B. Conforming implementations
MUST be able to parse all distinguished name attribute types that are
encoded in OID dotted decimal form, as well as all distinguished name
attribute values that are encoded in "#" hexadecimal form.
6.3.2. ski: Subject Key Identifier
The introducer production is "SKI:". The value production is the
hexadecimal encoding of the certificate's subject key identifier,
which is recorded in the certificate's Subject Key Identifier
extension (Section 4.2.1.2 of [RFC5280]). The octets are the DER-
encoded contents octets of the SubjectKeyIdentifier (OCTET STRING)
extension value. For a certificate that lacks a subject key
identifier, an underlying implementation MAY operatively associate a
subject key identifier with the certificate.
A conforming generator SHALL emit only hexadecimal encoded data,
i.e., the characters A-F (case-insensitive) and 0-9.
A conforming parser SHALL accept value productions that contain the
following non-hex digits: whitespace (HT, VT, SP, FF, CR, LF),
hyphen, and colon. A conforming parser MAY accept values that
contain other characters.
6.4. Path-Based Specifications
A certificate may be identified by a path to data. A conforming
parser MUST recognize file path, Registry, and URI specs, although
conforming implementations merely MAY process them.
Two common themes among path-based certspecs are that they may refer
to weakly typed or untyped data, and they have a higher probability
of referring to data that contains multiple certificates. Therefore,
a greater degree of content-sniffing is required for interoperability
than the certspecs above. An implementation that implements these
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path-based certspecs SHALL support the ASN.1 Certificate PDU when
public key certificates are being retrieved, and the ASN.1
AttributeCertificate PDU when attribute certificates are being
retrieved. Additionally, a conforming implementation SHALL support
the ASN.1 ContentInfo (PKCS #7/CMS SignedData) PDU.
Untyped binary data may be encoded in a [X.690] transfer syntax,
which may be BER, CER, or DER; for purposes of this section, these
are all called "BER-encoded".
6.4.1. File Path
File paths are identified by their introducer productions / \ [A-Z]:
./ ../ .\ ..\ ~ % and $. The characters that follow MUST be valid
path characters for the system on which the files are being accessed.
Since the starting character sequences for file paths are fixed and
determinable, prefixing the file path with a type identifier is
(thought to be) unnecessary.
A relative file path begins with "." or "..", and is relative to a
"current directory". Determining an appropriate "current directory"
is outside the scope of this specification.
When the file is read, implementations MUST accept the following,
regardless of the filename, which SHOULD NOT be the conclusive
determinant of the type:
1. Typed data (reported only by a minority of file systems), which
is treated conclusively as the type
2. Data that is determined to be textual, which is analyzed
according to [RFC7468]
3. Data that is determined to be BER-encoded
The manner of determining whether data is textual or BER-encoded data
is not fixed by this specification, but see, e.g., Appendix C.
File paths may have unexpanded environment variables, such as
%USERNAME% or ${LOGNAME}; implementations MUST parse these
environment variable syntaxes, but merely MAY perform environment
variable substitution as environment, capability, and security
concerns dictate.
Note that Unix-oriented file paths can contain "|" in the production
"\|", but this production is unambiguous with the pkcsattrs
delimiter. Windows-oriented file paths cannot contain "|".
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6.4.2. Registry
Certificates can be identified on Windows machines with Registry keys
and values. The introducer productions for local Registry entries
are "HKEY_LOCAL_MACHINE\", "HKEY_CURRENT_USER\",
"HKEY_CLASSES_ROOT\", "HKEY_USERS\", "HKEY_CURRENT_CONFIG\",
"HKLM:\", "HKCU:\", "HKCR:\", "HKU:\", and "HKCC:\". The introducer
productions for remote Registry entries are "\\", followed by a
computer name, followed by either "\HKLM:\" or "\HKU:\".
Registry key names include any printable character except backslash
"\"; each key includes what amounts to an associative array of
values, which are name/type/data tuples. A value name can include
any printable character, including "<", ">", and "|"; additionally,
every key has a default value, which has a zero-length name. This
layout presents a couple of parsing challenges.
A Registry production is comprised of a key path followed by a value.
The key path's key names are delimited by "\". In each key name,
"<", ">", and "|" SHALL be escaped with a preceding "\". The value
name is delimited from the key name with two backslashes "\\". "<",
">", "|", and "\" in the value SHALL be escaped with a preceding "\".
The default value MAY be identified with or without the two final
backslashes. Unlike file paths, Registry productions do not
recognize or substitute unexpanded environment variables.
Registry values have a type and some data. When the type is REG_SZ
or REG_EXPAND_SZ, an implementation is to treat the text firstly as a
recursive certspec or multispec. If it is not a certspec or
multispec, then an implementation is to analyze the text according to
[RFC7468]. Text in REG_EXPAND_SZ is subject to environment variable
substitution. When the type is REG_BINARY, an implementation is to
determine if the data is BER-encoded, and if so, to analyze it for
supported ASN.1 PDUs. When the type is REG_LINK, an implementation
is to follow the symbolic link.
6.4.3. URI
The introducer production is "URI:". The value is a URI-Template
production [RFC6570], which is to produce a [RFC3986] conforming URI-
reference production.
In the context of URIs, a relative reference conforms to the
relative-ref production of [RFC3986] and the usage described in
Section 4.2 of [RFC3986]; it is relative to a "base URI".
Determining an appropriate "base URI" is outside the scope of this
specification.
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When the URI is dereferenced, implementations MUST accept the
following, regardless of the path or query productions:
1. representations that are conclusively public key certificates or
attribute certificates, such as LDAP URIs [RFC4516] that point to
or contain userCertificate attributes (2.5.4.36, for public key
certificates) or attributeCertificate attributes (2.5.4.58, for
attribute certificates)
2. application/pkix-cert and application/pkix-attr-cert entities,
which are conclusively public key certificates or attribute
certificates, respectively
3. application/pkcs7-mime and application/cms entities, when the
body represents a ContentInfo/SignedData containing certificates
(regardless of the smime-type or encapsulatingContent parameters,
and regardless of whether or not the SignedData is in a
degenerate, certs-only format)
4. text/plain entities, which are analyzed according to [RFC7468]
5. Arbitrary data and application/octet-stream entities are treated
as untyped; they are are analyzed for textual or binary [X.690]
data
6. Arbitrary text, which is analyzed according to [RFC7468]
7. Arbitrary BER-encoded data, which is analyzed for supported ASN.1
PDUs
The URI certspec can include a fragment identifier. Implementations
MUST parse fragment identifiers, but merely MAY perform "secondary
resource" isolation and processing as environment, capability, and
security concerns dictate.
The URI certspec can be a URI Template [RFC6570]. Implementations
MUST parse URI templates, but merely MAY expand them in accordance
with [RFC6570] as environment, capability, and security concerns
dictate.
Note that URI templates can contain "|" in the production "{|".."}",
but this production is unambiguous with the pkcsattrs delimiter.
6.5. Algorithm for Distinguishing ASN.1 PDUs
A certspec can identify a public key certificate ("PKC") or an
attribute certificate ("AC"). When the type of certificate is
specified unambiguously in the source data, an implementation SHALL
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follow the specifier in the source data. However, of the certspecs
listed in this document, only a subset of URIs are capable of
unambiguous specification (e.g., via Internet media type designation
of application/pkix-cert or application/pkix-attr-cert). Most other
certspecs will return a blob of bytes or characters. Therefore, an
implementation needs to perform some content-sniffing to figure out
what the data represents. There are two (not entirely orthogonal)
decisions: is the data textual [RFC7468] or not, and does the data
represent a PKC or AC? (Note: The content-based certspecs BASE64 and
HEX always represent one certificate; the encodings MUST NOT encode a
textual blob or a PKCS #7/CMS PDU.)
This normative section addresses distinguishing PDU types when
applications encounter BER-encoded data that is not further typed.
An implementation MAY use any algorithm it chooses, as long as it
produces the same results. A suggested algorithm for distinguishing
textual data is in Appendix C; that algorithm is merely informative.
The algorithm for distinguishing ASN.1 PDUs is:
1. Ensure that the first octet is SEQUENCE 30h.
2. Ensure that the length covers the length of the data, minus the
tag and length octets. (If the length is indefinite, a check
that the end of the data has the end-of-contents octets would be
appropriate.) Extraneous data SHALL be considered erroneous.
3. If there are 2 elements -> confirm that the first element is
OBJECT IDENTIFIER 1.2.840.113549.1.7.2 and the second element is
explicitly tagged (APPLICATION 0, A0). Analyze the PDU as a
ContentInfo containing SignedData.
4. Otherwise, ensure that there are 3 elements, and that the first
element is a SEQUENCE 30h (either AttributeCertificateInfo or
TBSCertificate).
5. this SEQUENCE has: 6, 7, or 7+ elements
6. if 6 elements -> Analyze the PDU as a Certificate (public key
certificate) with version v1 (ABSENT).
7. if 7+ elements ->
1. look at version field (first element)
2. if INTEGER (UNIVERSAL 2) -> Analyze the PDU as an
AttributeCertificate (attribute certificate)
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3. if explicitly tagged (APPLICATION 0, A0) and the contents are
INTEGER (UNIVERSAL 2) -> Analyze the PDU as a Certificate
(public key certificate).
7. Other Certificate Specifications
The additional certificate specifications in this section are
provided for applications to use as local identifiers that are
useful, intuitive, or supportive of legacy systems or overriding
design goals. These certspecs SHOULD NOT be used for interchange.
7.1. DBKEY (Reserved)
The introducer production is "DBKEY:". The DBKEY certspec is meant
for an opaque string that serves as the unique key to a certificate
in an implementation's certificate database. This document reserves
this introducer sequence for future use.
7.2. SELECT (Reserved)
The introducer production is "SELECT" (without a colon). The SELECT
certspec is meant for a valid SQL statement (suitably escaped) that
retrieves a row representing a certificate. This document reserves
this introducer sequence for future use.
8. Multiple certspecs (multispec)
A multispec is a string that contains multiple certspecs, each of
which is intended to identify the exact same certificate. If
multiple certificates match a single spec, a single certificate can
be returned by the multispec access operation, so long as the
intersection of certificates identified by all of the certspecs in
the multispec is one. The purpose of multispec is to provide
multiple access and verification methods. For example, a hash
algorithm may have known weaknesses, but may be the most efficient
way to identify a certificate (e.g., because it is the index method).
Providing additional certspecs (i.e., strong hash algorithms) would
increase the certainty that the correct certificate is accessed.
Another example is to provide two URIs for a certificate: one that
works inside an organizational firewall, and one that works outside
an organizational firewall. Conforming applications MAY ignore
individual certspec lookup failures (where the certspec fails to
return any certificate due to error conditions) as environment,
capability, and security concerns dictate.
As the certspecs above make use of almost all other characters in the
ASCII range, < and > have been chosen to delimit certspecs between
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each other. (Whitespace can also appear between each < and >
delimited certspec.) The ABNF of multispec is:
multispec = 1*("<" certspec ">")
Figure 3: multispec ABNF
9. Attributes (pkcsattrs)
This specification defines a textual format for PKCS attributes.
This format is not limited to certificates: it can be used with other
PKCS-related data. The syntax is intended primarily to convey
certificate-related attributes found in PKCS #9 [RFC2985], PKCS #11
[PKCS11], PKCS #12 [RFC7292], and particular implementations of
cryptographic libraries. These attributes are syntactically
identical to, but semantically disjoint from, Directory (X.500/LDAP)
attributes.
When pkcsattrs is used with a certspec or multispec, the intent is to
associate arbitrary metadata with a certificate--metadata that is not
intrinsic to that certificate. For example, the additional
attributes may represent preferences. Attributes in this context are
semantically equivalent to PKCS #12 "bagAttributes", drawn from the
"PKCS12AttrSet" [RFC7292].
pkcsattrs are delimited from a certspec or multispec production with
"|". Each pkcsattr SHALL have a corresponding ASN.1 definition. The
textual syntax of pkcsattrs is very similar to (in fact, a superset
of) [RFC4514]: the pkcsattrs production represents the PKCS
Attributes family of types, which are repeatedly defined in those
standards, and standards that derive from them, as
SET SIZE (1..MAX) OF Attribute. E.g., CMS (from PKCS #7) [RFC5652],
private keys (from PKCS #8) [RFC5958], and PKCS #12 [RFC7292].
Attributes are semantically unordered. Multiple attributes are
separated with ",".
Each attribute has a single attrType (canonically defined as OBJECT
IDENTIFIER in [RFC5652]), and a SET OF attrValues. The attrType is
encoded as the string representation of AttributeType (that is,
either a registered short name (descriptor) [RFC4520], or the dotted-
decimal encoding, <numericoid> of the OBJECT IDENTIFIER [RFC4512]).
When an attribute has at least one value, the attrType is followed by
"=" and the encoding of the attrValues (empty strings are possible).
Multiple attrValues are separated by "+". When the attribute has no
values, the attrType MUST NOT be followed by "=".
An attrValue can have one of several encodings:
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hex: The attrValue can always be represented by "#" followed by the
hexadecimal encoding of each of the octets of the BER encoding of
the attrValue, following paragraph 1 of Section 2.4 of [RFC4514].
Implementations MUST support this encoding.
string: If the attrValue has a LDAP-specific string encoding, that
encoding can be used as the string representation of the value,
with characters suitably escaped according to paragraph 2 and
onward of Section 2.4 of [RFC4514]. Implementations SHOULD
support this encoding for attributes of interest to it.
XER: The attrValue can be represented by its BASIC-XER encoding
[X.693] (Clause 8). When in BASIC-XER encoding, the string MUST
be a complete XML fragment comprising one element, i.e., there
SHALL NOT be an XML prolog. XER encoding is self-delimiting
because it has balanced elements; this string always begins with
"<" and ends with ">". Processing is simplified compared to
arbitrary XML in that XML processing instructions, XML comments,
and CDATA sections are prohibited. Implementations MUST support
parsing through this encoding, but merely MAY support this
encoding (encoding and decoding between [X.690]) for attributes of
interest to it.
ASN.1 value: The attrValue can be represented by its ASN.1 value
notation [X.680], surrounded by exactly one space (SP) on each
end. The syntax is precisely defined in Figure 4 so that the
value itself never begins or ends with ASN.1 "white-space",
although "white-space" can occur within the value. ASN.1 value
notation requires a bit of finesse in that <"> can appear inside
to delimit "cstring" lexical items (see Clause 12.14 and Clause 41
of [X.680]). A "cstring" starts and ends with <">, and can
represent <"> internally with a pair of consecutive <">.
Therefore, <"> is balanced because it always occurs in multiples
of two. If the value is just a cstring, then the representation
will have exactly two <"> at the beginning, and two <"> at the
end, with evenly-balanced <"> pairs inside. Other values that are
not lists (enclosed with "{" and "}") do not have <"> occur within
them. Otherwise, the representation must have at least one "{"
"}" balanced pair at either end, hemming in <"> occurrences to
within the balanced pairs of "{" and "}". Implementations MUST
support parsing through this encoding, but merely MAY support this
encoding (encoding and decoding between [X.690]) for attributes of
interest to it.
Of the attrValue encodings listed above, only "hex" can reliably
transfer the underlying BER representation without an implementation
maintaining specific knowledge of every attribute. Therefore, "hex"
is RECOMMENDED for open interchange of pkcsattrs. The other
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representations are really meant for human production and
consumption.
9.1. ABNF
The collective ABNF of pkcsattrs is:
pkcsattrs = pkcsattr ["," pkcsattrs]
pkcsattr = pkcsattrType ["=" pkcsattrValues]
pkcsattrType = descr / numericoid
pkcsattrValues = pkcsattrValue ["+" pkcsAttrValues]
pkcsattrValue = hexstring / string /
basic-xer-string / asn1-value-string
basic-xer-string = xer-element
; limited by [X.680][X.693]
xer-Name = ALPHA *(ALPHA / DIGIT / "_" / "-" / ".")
; limited by XML to these four chars
xW = *(HT / LF / CR / SP)
xer-element = xer-EmptyElemTag / xer-STag xer-content xer-ETag
xer-EmptyElemTag = "<" xer-Name xW "/>"
xer-STag = "<" xer-Name xW ">"
xer-content = *xer-CharData *((xer-element / xer-Reference)
*xer-CharData)
xer-ETag = "</" xer-Name xW ">"
xer-CharData = HT / LF / CR / %x20-25 / %x27-3B / "=" / %x3F-D7FF /
%xE000-%xFFFD / %x10000-10FFFF
xer-Reference = xer-EntityRef / xer-CharRef
xer-EntityRef = "&" (%s"amp" / %s"lt" / %s"gt") ";"
xer-CharRef = "&#" (1*DIGIT / %s"x" 1*HEXDIG) ";"
; TODO: may want another delimiter--think about it
; uses num from above for non-negative integers
asn1-value-string = SP aValue aW
; identifier, Clause 12.3 of [X.680]
aid = %x61-7A *(["-"] (ALPHA / DIGIT))
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; "newline", Clause 12.1.6 of [X.680]
; (NEL LS PS omitted)
aNL = %d10-13
; single "white-space" (comment considered matching,
; because delimits lexical items), Clause 12.1.6 of [X.680]
aS = %d9-13 / SP / NBSP / acomment
aW = *aS
acomment = "--" *(["-"] ( UWSP / %x21-2C / %x2E-7E /
UVCHARBEYONDASCII / PUACHAR ) )
(aNL / "-" (aNL / "-"))
; space in unicode: 85 A0 1680 2000-200A 202F 205F 3000
; related not-unicode-White_Space-but-whitespace
; 180E 200B-200D 2060 FEFF
; uses "white-space" above, but "comment" not relevant
acstring = %x22 *(UWSP / aNL / %x21 / %x22.x22 / %x23-7E /
UVCHARBEYONDASCII) %x22
aValue = %s"TRUE" / %s"FALSE" / %s"NULL" / %s"PLUS-INFINITY" /
%s"MINUS-INFINITY" / %s"NOT-A-NUMBER" /
"'" *("0" / "1" / aW) "'B" / "'" *(HEXDIG / aW) "'H" /
%s"CONTAINING" 1*aS aValue /
aid [aW ":" aW aValue] /
aNumericRealValue / acstring / "{" aW alist "}"
; ObjIdComponents [X.680]
; aOIDC
aObjIdComponents = (num / aid) [aW "(" aW (num/aid) aW ")"]
; NumericRealValue [X.680]
; TODO: integer part could be 1*DIGIT or num
aNumericRealValue = ["-" aW] 1*DIGIT ["."] *DIGIT ["e" ["-"] num]
; *List values [X.680]
alist = aValue aW *("," aW aValue aW) /
aid 1*aS aValue aW *("," aW aid 1*aS aValue aW) /
; aOIDC *(1*aS aOIDC) aW
aObjIdComponents *(1*aS aObjIdComponents) aW
Figure 4: pkcsattrs ABNF
9.2. Mandatory Attribute Support
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9.2.1. In General
Attributes related to certificate objects are in the domain of PKCS
attributes, not Directory name attributes. [I-D.seantek-ldap-pkcs9]
discusses the problem and registers attributes that are specifically
designated for PKCS use, rather than Directory use.
A conforming implementation is expected to recognize the short names
(descriptors) recorded in the LDAP Parameters: Object Identifier
Descriptors registry [LDAPDESC] that are designated for PKCS use if
the implementation processes that attribute. Not all attributes are
needed by all implementations. For example, a CMS processing
application that supports pkcsattrs needs to recognize contentType
and messageDigest, but not extendedCertificateAttributes.
9.2.2. For Certificate Applications
A conforming implementation that supports pkcsattrs for certificates
SHALL process the following attributes from PKCS #9 [RFC2985],
including recognizing the following short names (descriptors) and
associated LDAP-specific string encodings.
friendlyName (1.2.840.113549.1.9.20)
localKeyId (1.2.840.113549.1.9.21)
signingDescription (1.2.840.113549.1.9.13)
smimeCapabilities (1.2.840.113549.1.9.15)
[[NB: smimeCapabilities does not have a SYNTAX with an LDAP-
specific encoding. ASN.1 value notation is probably the most
readable alternative, but support for ASN.1 value notation remains
OPTIONAL.]]
9.3. Canonicalization
The pkcsattrs production is a textual encoding of the ASN.1
SET SIZE (1..MAX) OF Attribute. The textual format in this section
is not intended to be used as any kind of canonical form. The
canonical form is the DER encoding of the corresponding
SET SIZE (1..MAX) OF Attribute.
10. Whitespace
This specification is intended for textual data that may be visible
to or edited by humans. Whitespace is a key factor in usability, so
this specification permits whitespace in certain productions.
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The certspec, multispec, pkcsattrs, and certstring productions are
ideally emitted as one (long) line. The overall intent is that a
bare line break (without leading or trailing horizontal space) is
supposed to delimit these productions from each other.
If it is desirable to break one of these productions across multiple
lines, a hanging indent SHALL be used at syntactically appropriate
places. A hanging indent means a newline production (LF, CRLF, or
other characters appropriate to the character set, e.g., [[UNICODE]])
followed by one or more horizontal space characters. The preferred
horizontal space production is a single SP character.
Generally, where whitespace is permitted, the whitespace either has
no semantic meaning and therefore can be collapsed to a zero-length
substring, i.e., skipped, or can be folded into a single whitespace
character, i.e., a single SP.
Productions that represent the hexadecimal (or base64) encodings of
octets MAY have arbitrary whitespace interspersed between the
hexadecimal (or base64) characters. The whitespace has no semantic
meaning, and can be collapsed. Certspec and pkcsattrs parsers that
parse "#" delimited attribute values in distinguished names and
certificate attributes MAY accept and collapse whitespace; however,
such whitespace is not permitted by [RFC4514]. Note that the
attribute value MUST begin with "#"; there MUST NOT be leading
whitespace.
A parser MAY accept whitespace preceding the pkcsattrType production
in pkcsattrs.
A parser MAY accept whitespace between each angle-bracket-delimited
certspec in the multispec production.
A parser MAY accept whitespace preceding the attributeType production
in distinguishedName.
Generally, whitespace characters in values are otherwise considered
to be semantically meaningful. A generator SHOULD encode such
characters (e.g., with hexpair [RFC4514]) to avoid ambiguity or
corruption.
11. Guidelines for Extending certspec
The certspec definition presented in this document is intended to be
fairly comprehensive. Nevertheless, there are several points of
extension for implementors who may want to identify a certificate
with more than what is presented in this document.
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Firstly, certspec is naturally extended by supporting additional hash
algorithms. The hash introducer characters are tied to the Hash
Function Textual Names Registry; adding a new hash algorithm to that
registry is necessary for certificates to get identified with that
hash algorithm under this specification. For security reasons, the
introducers "MD2" and "MD5" SHALL NOT be generated or parsed. See
[RFC6149] and [RFC6151].
Secondly, certspec allows for the full range of "local" identifiers
(i.e., file paths, which may not actually be local) and "network"
identifiers (i.e., URIs, which may not actually need the network). A
certspec implementation that can make use of these facilities can
naturally be extended by extending the path (e.g., with pipes and
mount points) or the URI topology (e.g., with novel URI schemes).
The ISSUERSN, SUBJECTEXP, and HOLDEREXP certspecs provide
opportunities to identify the issuer, subject, or holder using
multiple methods. An implementation MAY support other productions
that equate to issuer certificates, subject identifiers, or holder
sub-fields.
Implementations MAY recognize other types of certspecs. However, new
types intended for open interchange require an update to this
document.
A new certspec SHALL satisfy the following criteria:
1. The type is identified by a keyword, followed by ":", or, the
type is identified by very short sequences of characters that
unambiguously signal the type of the certspec value (as file
paths and Registry keys and values currently do). The
specification MUST state whether the introducer characters are
case-sensitive.
2. The characters "<", ">", and "|" need to be distinguishable from
their uses in multispec and pkcsattrs (certstring) using a
context-free grammar, e.g., ABNF.
3. [[TODO: further elaborate, or remove.]] If internal whitespace
(including line-breaking) is permitted, the internal whitespace
is consistent with this specification.
12. Use of certspec in Systems
certspec is useful wherever a system may need to include or refer to
a certificate. Some systems may wish to refer to a certificate
without enabling all of the expressive power (and security
considerations) of all strings in this specification. Accordingly,
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those systems and specifications SHOULD develop profiles of this
specification.
This document guarantees that the introducer characters "URN:" and
"CERT:" are RESERVED and will never be used. Implementors MUST take
note that a raw certspec is not a valid URI: certspec-types are not
registered URI schemes, have a broader character repertoire than
permitted by [RFC3986], and do not have the same semantics as URIs.
13. IANA Considerations
Appendix D proposes modifications to the application/pkcs12 media
type to support labeling a degenerate syntax that only contains
certificates and certificate revocation lists. IANA is asked to
update the fields of the application/pkcs12 registration as follows:
Optional parameters:
profile: A profile of PKCS #12 for particular applications.
When this parameter has value "certs-only", then it conforms
to the profile in Appendix E of [[RFC Ed: this document]].
If a filename is supplied, the file extension is to be .p12c;
appropriate description strings (in US-English) might be
"PKCS #12 Certificate Store" or
"PKCS #12 Certificate Data with Attributes", among others.
It would be inappropriate to imply that such content
contains keys or other secret materials.
This parameter is case sensitive.
Published specification:
PKCS #12 v1.0, June 1999; PKCS #12 v1.1 (RFC 7292), July 2014
[[RFC Ed: add reference to this document.]]
Additional information:
Deprecated alias names for this type: N/A
Magic number(s): None.
File extension(s): .p12 or .pfx; .p12c (in profile=certs-only case)
Macintosh file type code(s): N/A
Figure 5: application/pkcs12 Media Type Registration
Appendix D proposes modifications to the application/cms media type
to support SafeContents as a CMS inner content type. IANA is asked
to update the CMS Inner Content Types sub-registry by adding an
identifier "safeContents" with the object identifier listed in
Appendix D. IANA is further asked to update the application/cms
media type registration template accordingly.
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14. Security Considerations
Digital certificates are important building blocks for
authentication, integrity, authorization, and (occasionally)
confidentiality services. Accordingly, identifying digital
certificates incorrectly can have significant security ramifications.
When using hash-based certspecs, the cryptographic hash algorithm
MUST be implemented properly and SHOULD have no known attack vectors.
For this reason, algorithms that are considered "broken" as of the
date of this Internet-Draft, such as MD2 [RFC6149] and MD5 [RFC6151],
are precluded from being valid certspecs. The registration of a
particular algorithm spec in this namespace does NOT mean that it is
acceptable or safe for every usage, even though this Internet-Draft
requires that a conforming implementation MUST implement certain
specs.
When using content-based certspecs, the implementation MUST be
prepared to process strings of arbitrary length. As of this writing,
useful certificates rarely exceed 10KB, and most implementations are
concerned with keeping certificate sizes down. However, a
pathological or malicious certificate could easily exceed these
metrics.
When using element-based certspecs, the implementation MUST be
prepared to deal with multiple found certificates that contain the
same certificate data, but are not the same certificate. In such a
case, the implementation MUST segregate these certificates so that
the implementation only continues with certificates that it considers
valid or trustworthy (as discussed further below). If, despite this
segregation, multiple valid or trustworthy certificates match the
certspec, the certspec (not in a multispec) MUST be rejected, because
a certspec is meant to identify exactly one certificate (not a family
of certificates).
Certificates identified by certspecs should only be used with an
analysis of their validity, such as by computing the Certification
Path Validation Algorithm (Section 6 of [RFC5280]) or by other means.
For example, if a certificate database contains a set of certificates
that it considers inherently trustworthy, then the inclusion of a
certificate in that set makes it trustworthy, regardless of the
results of the Certification Path Validation Algorithm. Such a
database is frequently used for "Root CA" lists.
Conveying PKCS attributes with certificates will likely have security
effects. For example, some implementations display the friendlyName
attribute to a user on par with or in lieu of data derived from the
certificate itself. Other implementations allow certificates to be
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identified by this friendlyName attribute. Therefore, blind
acceptance of PKCS attributes without considering the source or
content can result in security compromises.
15. References
15.1. Normative References
[I-D.seantek-abnf-more-core-rules]
Leonard, S., "Comprehensive Core Rules and References for
ABNF", draft-seantek-abnf-more-core-rules-06 (work in
progress), September 2016.
[I-D.seantek-ldap-pkcs9]
Leonard, S., "Lightweight Directory Access Protocol (LDAP)
Registrations for PKCS #9", draft-seantek-ldap-pkcs9-05
(work in progress), June 2016.
[I-D.seantek-unicode-in-abnf]
Leonard, S. and P. Kyzivat, "Unicode in ABNF", draft-
seantek-unicode-in-abnf-00 (work in progress), September
2016.
[LDAPDESC]
IANA, "LDAP Parameters: Object Identifier Descriptors",
<http://www.iana.org/assignments/
ldap-parameters#ldap-parameters-3>.
[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, DOI 10.17487/RFC2045, November 1996,
<http://www.rfc-editor.org/info/rfc2045>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66, RFC
3986, January 2005.
[RFC4512] Zeilenga, K., "Lightweight Directory Access Protocol
(LDAP): Directory Information Models", RFC 4512, June
2006.
[RFC4514] Zeilenga, K., "Lightweight Directory Access Protocol
(LDAP): String Representation of Distinguished Names", RFC
4514, June 2006.
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[RFC4520] Zeilenga, K., "Internet Assigned Numbers Authority (IANA)
Considerations for the Lightweight Directory Access
Protocol (LDAP)", BCP 64, RFC 4520, DOI 10.17487/RFC4520,
June 2006, <http://www.rfc-editor.org/info/rfc4520>.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, October 2006.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, May 2008.
[RFC5750] Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet
Mail Extensions (S/MIME) Version 3.2 Certificate
Handling", RFC 5750, January 2010.
[RFC5755] Farrell, S., Housley, R., and S. Turner, "An Internet
Attribute Certificate Profile for Authorization", RFC
5755, January 2010.
[RFC6570] Gregorio, J., Fielding, R., Hadley, M., Nottingham, M.,
and D. Orchard, "URI Template", RFC 6570, DOI 10.17487/
RFC6570, March 2012,
<http://www.rfc-editor.org/info/rfc6570>.
[RFC7405] Kyzivat, P., "Case-Sensitive String Support in ABNF", RFC
7405, DOI 10.17487/RFC7405, December 2014,
<http://www.rfc-editor.org/info/rfc7405>.
[RFC7468] Josefsson, S. and S. Leonard, "Textual Encodings of PKIX,
PKCS, and CMS Structures", RFC 7468, DOI 10.17487/RFC7468,
April 2015, <http://www.rfc-editor.org/info/rfc7468>.
[SHS] National Institute of Standards and Technology, "Secure
Hash Standard", Federal Information Processing Standard
(FIPS) 180-4, March 2012,
<http://csrc.nist.gov/publications/fips/fips180-4/
fips-180-4.pdf>.
15.2. Informative References
[PKCS11] RSA Laboratories, "PKCS #11 v2.30: Cryptographic Token
Interface Standard", PKCS 11, April 2009.
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[RFC1421] Linn, J., "Privacy Enhancement for Internet Electronic
Mail: Part I: Message Encryption and Authentication
Procedures", RFC 1421, February 1993.
[RFC1738] Berners-Lee, T., Masinter, L., and M. McCahill, "Uniform
Resource Locators (URL)", RFC 1738, December 1994.
[RFC2253] Wahl, M., Kille, S., and T. Howes, "Lightweight Directory
Access Protocol (v3): UTF-8 String Representation of
Distinguished Names", RFC 2253, December 1997.
[RFC2985] Nystrom, M. and B. Kaliski, "PKCS #9: Selected Object
Classes and Attribute Types Version 2.0", RFC 2985,
November 2000.
[RFC4516] Smith, M. and T. Howes, "Lightweight Directory Access
Protocol (LDAP): Uniform Resource Locator", RFC 4516, June
2006.
[RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
RFC 5652, September 2009.
[RFC5958] Turner, S., "Asymmetric Key Packages", RFC 5958, August
2010.
[RFC6149] Turner, S. and L. Chen, "MD2 to Historic Status", RFC
6149, DOI 10.17487/RFC6149, March 2011,
<http://www.rfc-editor.org/info/rfc6149>.
[RFC6151] Turner, S. and L. Chen, "Updated Security Considerations
for the MD5 Message-Digest and the HMAC-MD5 Algorithms",
RFC 6151, March 2011.
[RFC7292] Moriarty, K., Nystrom, M., Parkinson, S., Rusch, A., and
M. Scott, "PKCS #12: Personal Information Exchange Syntax
v1.1", RFC 7292, July 2014.
[UNICODE] The Unicode Consortium, "The Unicode Standard, Version
8.0.0", ISBN 978-1-936213-10-8, August 2015.
Mountain View, CA: The Unicode Consortium.
[X.501] International Telecommunication Union, "Information
technology - Open Systems Interconnection - The Directory:
Models", ITU-T Recommendation X.501, ISO/IEC 9594-2,
October 2012, <https://itu.int/ITU-T/X.501>.
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[X.680] International Telecommunication Union, "Information
technology - Abstract Syntax Notation One (ASN.1):
Specification of basic notation", ITU-T Recommendation
X.680, ISO/IEC 8824-1, August 2015, <https://itu.int/ITU-
T/X.680>.
[X.690] International Telecommunication Union, "Information
technology - ASN.1 encoding rules: Specification of Basic
Encoding Rules (BER), Canonical Encoding Rules (CER) and
Distinguished Encoding Rules (DER)", ITU-T Recommendation
X.690, ISO/IEC 8825-1, August 2015, <https://itu.int/ITU-
T/X.690>.
[X.693] International Telecommunication Union, "Information
technology - ASN.1 encoding rules: XML Encoding Rules
(XER)", ITU-T Recommendation X.693, ISO/IEC 8825-4, August
2015, <https://itu.int/ITU-T/X.693>.
Appendix A. Mandatory Attribute Descriptors for Distinguished Names
As per [RFC4514], attribute descriptors case-insensitive. A
conformant implementation MUST recognize the attributes in the table
below when parsing certspecs containing distinguished names, both by
the OIDs and by the names recorded in the LDAP Parameters: Object
Identifier Descriptors registry [LDAPDESC]. A conforming generator
SHOULD emit these attribute descriptors in lieu of their dotted
decimal representations.
+----------------------------+-------------------------------+------+
| OID | Names | RFC |
+----------------------------+-------------------------------+------+
| 2.5.4.3 | cn (CN) | 4514 |
| | commonName | |
| 2.5.4.7 | l (L) | 4514 |
| | localityName | |
| 2.5.4.8 | st (ST) | 4514 |
| | (S)* | |
| | stateOrProvinceName | |
| 2.5.4.10 | o (O) | 4514 |
| | organizationName | |
| 2.5.4.11 | ou (OU) | 4514 |
| | organizationalUnitName | |
| 2.5.4.6 | c (C) | 4514 |
| | countryName | |
| 2.5.4.9 | street (STREET) | 4514 |
| | streetAddress | |
| 0.9.2342.19200300.100.1.25 | dc (DC) | 4514 |
| | domainComponent | |
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| 0.9.2342.19200300.100.1.1 | uid (UID) | 4514 |
| | userId | |
| 2.5.4.5 | serialNumber (SERIALNUMBER) | 5280 |
| 2.5.4.46 | dnQualifier (DNQUALIFIER) | 5280 |
| 2.5.4.4 | sn (SN) | 5280 |
| | surname | |
| 2.5.4.42 | gn (GN)** | 5280 |
| | givenName | |
| 2.5.4.12 | (T)* | 5280 |
| | title | |
| 2.5.4.43 | (I)* | 5280 |
| | initials | |
| 2.5.4.44 | (GENQUALIFIER)* | 5280 |
| | generationQualifier | |
| | (GENERATIONQUALIFIER) | |
| 2.5.4.65 | (PNYM)* | 5280 |
| | pseudonym (PSEUDONYM) | |
| 1.2.840.113549.1.9.1 | (E)* | 5750 |
| | emailAddress | |
| | email | |
+----------------------------+-------------------------------+------+
Names in parentheses are variations that are not assigned as such in
[LDAPDESC]. Implementations MAY parse these names, but SHOULD NOT
generate them.
Names in ALL-CAPS may be emitted by some certificate-processing
applications; these names are compatible with lowercase or mixed-case
variations due to case-insensitivity.
* Name may appear in some implementations, but is not in [LDAPDESC].
** Name commonly appears in implementations, but is RESERVED in
[LDAPDESC]. Conforming implementations MAY generate this name from
2.5.4.42 and MUST parse this name as 2.5.4.42, despite its RESERVED
status.
Table 1: Attribute Descriptors
Appendix B. Recommended Attribute Descriptors for issuersn certspec
As per [RFC4514], attribute descriptors are case-insensitive.
[[TODO: complete. Probably date of birth, place of birth, gender,
etc. are already defined elsewhere. Also jurisdictionLocalityName,
etc. from CABForum.]]
Appendix C. Suggested Algorithm for Distinguishing Textual Data
This appendix provides an informative algorithm that implementations
MAY use to content-sniff textual data. This appendix is a companion
to Section 6.5.
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Some certspecs will return arbitrary data, which might be textual in
nature. This is especially true of the file path and URI specs.
There are historical reasons for this, mostly boiling down to "DER"
vs. "PEM" output options in popular cryptographic software packages,
without clear guidance on file extensions.
The only BER-encoded PDUs that are mandated by this spec are
Certificate [RFC5280], AttributeCertificate [RFC5755], and
ContentInfo (containing SignedData) [RFC5652]. Before trying to do
charset-sniffing, it is reasonable to probe for BER decoding first to
see what happens. The (normative) algorithm in Section 6.5 is a
sufficient test. At the very least, an implementation ought to check
for the presence of the SEQUENCE octet (30h), a valid length that
covers the length of the data, minus the tag and length octets, and
two or three validly-encoded tag-length-value elements (Clause 8.1.1
of [X.690]) inside the SEQUENCE.
Although an implementation can ingest arbitrary text containing
certificates, this specification only requires [RFC7468], which
requires the presence of encapsulation boundaries. An implementation
ought to look for Unicode byte order marks first; failing that, it
ought to consider ASCII, basically ignoring invalid byte sequences
that do not appear in [RFC7468] productions. Regardless of the
charset(s) chosen, an implementation can hunt for the minimum string
"-----BEGIN " followed somewhere by "-----END ", since those strings
are required for [RFC7468] conformance.
Appendix D. Binary Formats for Conveying Certificates with Attributes
During the development of this document, the author noted that there
is a lack of standardization around conveying attributes with
certificates. The bulk of this specification can be used to convey
such attributes in text; however, a binary format is also desirable.
Because the attributes in Section 9 are semantically equivalent to
PKCS #12 "bagAttributes", it makes sense to reuse this structure of
PKCS #12, if possible.
D.1. PKCS #12 certs-only Profile
Predecessors to PKCS #12 have been criticized for being too obtuse
and cumbersome to implement. This section proposes a profile of PKCS
#12 for a degenerate case of the syntax that only conveys
certificates and certificate revocation lists. It is analogous to
the degenerate case of SignedData in CMS [RFC5652]. The overall
usability goal is to convey certificates with attributes without
requiring user input of secret or private material (i.e., a password
or private key) to receive the data. The data MAY be signed for
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integrity protection, so long as verifying the signature does not
require user input of secret or private material.
To compose the degenerate case, the following structures in the "PFX"
structure are limited:
1. authSafe has contentType id-data or id-signedData (if signed),
containing an AuthenticatedSafe.
2. The AuthenticatedSafe SHALL contain exactly one ContentInfo,
which has contentType id-data, containing a SafeContents.
3. The SafeContents can contain any number of SafeBags.
4. Each SafeBag can only contain a certificate (via certBag) or a
certificate revocation list (via crlBag).
5. macData SHALL be "ABSENT".
[RFC7292] does not have an identifier for attribute certificates in
the CertBag. The ASN.1 module is hereby modified to support
attribute certificates:
attributeCertificate BAG-TYPE ::=
{OCTET STRING IDENTIFIED BY {certTypes 3}} -- 3 is TBD
-- DER-encoded attribute certificate stored in OCTET STRING
CertTypes BAG-TYPE ::= {
x509Certificate |
sdsiCertificate,
...,
attributeCertificate,
... }
Figure 6: PKCS #12 ASN.1 Module Modification
Implementations MUST parse through certBag elements containing
attribute certificates (MUST NOT fail parsing), but actually
processing attribute certificates is OPTIONAL if an implementation
has no need for them. (The same remarks apply to certificate
revocation lists.) Because this profile does not use encryption or
key derivation functions, conforming implementations do not need to
support such algorithms, which should greatly simplify
implementations.
It is desirable to convey this degenerate PKCS #12 data in MIME
entities and files. Since this format has very different usability
properties from full-featured PKCS #12, it is not to be labeled as
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standard PKCS #12. A new "profile" optional parameter with value
"certs-only" is proposed for the application/pkcs12 media type, as
well as a new file extension .p12c. See Section 13 for the modified
registration template.
D.2. CMS SafeContents contentType
Some applications will not want to bother with the PFX PDU of PKCS
#12 at all. For those applications, it is possible to transmit
SafeContents directly as CMS (PKCS #7) content.
The CMS (TBD: or PKCS #12?) ASN.1 module is hereby enhanced to
include an object identifier for SafeContents as a content type:
IMPORTS
SafeContents, bagtypes
FROM PKCS-12 {1 2 840 113549 1 pkcs-12(12) modules(0) pkcs-12(1)}
ContentSet CONTENT-TYPE ::= {
-- Define the set of content types to be recognized.
ct-Data | ct-SignedData | ct-EncryptedData | ct-EnvelopedData |
ct-AuthenticatedData | ct-DigestedData | ct-SafeContents, ... }
ct-SafeContents CONTENT-TYPE ::=
{ SafeContents IDENTIFIED BY id-safeContents }
-- could be 1.2.840.113549.1.12.10.1.6 existing safeContentsBag OID,
-- or a new 1.2.840.113549.1.12.10.2,
-- or a new 1.2.840.113549.7.9 from PKCS #7,
-- or a new 1.2.840.113549.1.9.16.1.37 from pkcs-9 smime ct
id-safeContents OBJECT IDENTIFIER ::= {bagtypes 6}
Figure 7: CMS ASN.1 Module Modification
SafeContents is registered as a CMS Inner Content Type (ICT) with the
identifier "safeContents". See Section 13 for the relevant
registration and application/cms modification.
Using this technique allows SafeContents directly in CMS content.
Any kind of SafeBag is permitted inside; unlike Appendix D.1, this
format is not further profiled.
D.3. SafeContents-to-PKCS#12 BER Adapter
An application that processes a SafeContents PDU directly may find it
expedient to adapt it to a PFX PDU for ingestion into legacy code
that only processes PKCS #12 data. The following adapter can be used
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for that purpose. Octets are listed in hexadecimal. Place the BER
encoding of SafeContents in the position marked "(SafeContents)".
The placeholders "LEN-" are [X.690] length octets, which are to be
computed as follows:
LEN-SC: The length in octets of the SafeContents.
LEN-2: LEN-SC plus the length in octets of LEN-SC itself, plus 1.
LEN-3: LEN-2 plus the length in octets of LEN-2 itself, plus 20.
LEN-4: LEN-3 plus the length in octets of LEN-3 itself, plus 1.
30 80 02 01 03 30 80 06092A864886F70D010701 A0 LEN-4 04 LEN-3
30 80 30 80 06092A864886F70D010701 A0 LEN-2 04 LEN-SC
(SafeContents)
0000 0000 0000 0000
Figure 8: BER Adapter
Appendix E. Textual Encoding of Attributes
[[TODO: Consider removing this appendix; Section 9 is clearer.]]
From time to time, it is desirable to convey attributes independently
of other PKIX, PKCS, or CMS structures. This appendix defines a
textual encoding [RFC7468] format for attributes.
Attributes are encoded using the "ATTRIBUTES" label. The encoded
data MUST be a BER (DER strongly preferred; see Appendix B of
[RFC7468]) encoded ASN.1 "SET OF Attribute", or, in rare cases,
"SEQUENCE OF Attribute" structure as described throughout Directory,
PKIX, PKCS, and CMS standards. Unless the collection is specifically
ordered, emitting the "SET OF Attribute" variant is RECOMMENDED.
No IETF document formally discusses what an attribute is (although
[RFC4512] comes close). Workable definitions can be gleaned from
[X.501] and [RFC4512]:
Each attribute [in the Directory] provides a piece of information
about, or describes a particular characteristic of, the object to
which the entry corresponds. --Clause 8.2 of [X.501]
An attribute consists of an _attribute type_, which identifies the
class of information given by an attribute, and the corresponding
_attribute values_, which are the particular instances of that
class of information appearing in the attribute within the entry.
--Clause 8.2 of [X.501]
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An entry [in the Directory] consists of a set of attributes that
hold information about the object that the entry represents.
--Section 2.2 of [RFC4512]
An attribute is an attribute description (a type and zero or more
options) with one or more associated values. An attribute is
often referred to by its attribute description. --Section 2.2 of
[RFC4512]
An attribute is comprised of a type and a SET OF values. The
collection of values is always unordered. Collections of attributes
are almost always unordered, and are almost always stored in a
"SET OF Attribute". A few protocols store attributes in a
"SEQUENCE OF Attribute", but for nearly all cases, the ordering is
stated to be irrelevant by the relevant standard document.
The attribute type is a widely shared protocol element in LDAP/
Directory, PKIX, PKCS, and CMS standards. However, the collections
of relevant attributes to particular occurrences of the structure (as
represented by a table constraint on an occurence) are largely
disjoint from one another. CMS attribute collections (e.g.,
"SignedAttributes", "UnsignedAttributes", "UnprotectedAttributes")
share no common semantics with Directory attributes, for instance.
The textual encoding provided in this section is appropriate for any
collection of attributes, but only context can determine what kinds
of attributes are appropriate, as well as the identity of the
corresponding object. Figure 9 provides an example of the textual
encoding, along with its corresponding Section 9 format.
localKeyId=#0402534C,friendlyName=Chubby\F0\9F\90\B0
-----BEGIN ATTRIBUTES-----
MTQwEQYJKoZIhvcNAQkVMQQEAlNMMB8GCSqGSIb3DQEJFDESHhAAQwBoAHUAYgBi
AHnYPdww
-----END ATTRIBUTES-----
Figure 9: Attributes Example
Author's Address
Sean Leonard
Penango, Inc.
5900 Wilshire Boulevard
21st Floor
Los Angeles, CA 90036
USA
Email: dev+ietf@seantek.com
URI: http://www.penango.com/
Leonard Expires September 14, 2017 [Page 35]
