Network Working Group J. Yasskin
Internet-Draft K. Ueno
Intended status: Standards Track Google
Expires: October 8, 2018 April 06, 2018
Signed HTTP Exchanges Implementation Checkpoints
draft-yasskin-httpbis-origin-signed-exchanges-impl-00
Abstract
This document describes checkpoints of
[I-D.yasskin-http-origin-signed-responses] to synchronize
implementation between clients, intermediates, and publishers.
Note to Readers
Discussion of this draft takes place on the HTTP working group
mailing list (ietf-http-wg@w3.org), which is archived at
https://lists.w3.org/Archives/Public/ietf-http-wg/ [1].
The source code and issues list for this draft can be found in
https://github.com/WICG/webpackage [2].
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
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on October 8, 2018.
Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Signing an exchange . . . . . . . . . . . . . . . . . . . . . 3
3.1. The Signature Header . . . . . . . . . . . . . . . . . . 4
3.1.1. Examples . . . . . . . . . . . . . . . . . . . . . . 5
3.1.2. Open Questions . . . . . . . . . . . . . . . . . . . 5
3.2. CBOR representation of exchange headers . . . . . . . . . 6
3.2.1. Example . . . . . . . . . . . . . . . . . . . . . . . 6
3.3. Loading a certificate chain . . . . . . . . . . . . . . . 7
3.4. Canonical CBOR serialization . . . . . . . . . . . . . . 8
3.5. Signature validity . . . . . . . . . . . . . . . . . . . 9
3.5.1. Open Questions . . . . . . . . . . . . . . . . . . . 12
3.6. Updating signature validity . . . . . . . . . . . . . . . 12
3.6.1. Examples . . . . . . . . . . . . . . . . . . . . . . 13
3.7. The Accept-Signature header . . . . . . . . . . . . . . . 14
4. Cross-origin trust . . . . . . . . . . . . . . . . . . . . . 14
4.1. Stateful header fields . . . . . . . . . . . . . . . . . 15
4.2. Certificate Requirements . . . . . . . . . . . . . . . . 16
5. Transferring a signed exchange . . . . . . . . . . . . . . . 16
5.1. Same-origin response . . . . . . . . . . . . . . . . . . 16
5.2. HTTP/2 extension for cross-origin Server Push . . . . . . 16
5.3. application/signed-exchange format . . . . . . . . . . . 16
6. Security considerations . . . . . . . . . . . . . . . . . . . 17
7. Privacy considerations . . . . . . . . . . . . . . . . . . . 17
8. IANA considerations . . . . . . . . . . . . . . . . . . . . . 18
8.1. Internet Media Type application/signed-exchange . . . . . 18
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
9.1. Normative References . . . . . . . . . . . . . . . . . . 19
9.2. Informative References . . . . . . . . . . . . . . . . . 21
9.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 22
Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 23
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23
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1. Introduction
Each version of this document describes a checkpoint of
[I-D.yasskin-http-origin-signed-responses] that can be implemented in
sync by clients, intermediates, and publishers. It defines a
technique to detect which version each party has implemented so that
mismatches can be detected up-front.
2. Terminology
Publisher The entity that controls the server for a particular
origin [RFC6454]. The publisher can get a CA to issue
certificates for their private keys and can run a TLS server for
their origin.
Exchange (noun) An HTTP request/response pair. This can either be a
request from a client and the matching response from a server or
the request in a PUSH_PROMISE and its matching response stream.
Defined by Section 8 of [RFC7540].
Intermediate An entity that fetches signed HTTP exchanges from an
publisher or another intermediate and forwards them to another
intermediate or a client.
Client An entity that uses a signed HTTP exchange and needs to be
able to prove that the publisher vouched for it as coming from its
claimed origin.
Unix time Defined by [POSIX] section 4.16 [3].
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Signing an exchange
In the response of an HTTP exchange the server MAY include a
"Signature" header field (Section 3.1) holding a list of one or more
parameterised signatures that vouch for the content of the exchange.
Exactly which content the signature vouches for can depend on how the
exchange is transferred (Section 5).
The client categorizes each signature as "valid" or "invalid" by
validating that signature with its certificate or public key and
other metadata against the exchange's headers and content
(Section 3.5). This validity then informs higher-level protocols.
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Each signature is parameterised with information to let a client
fetch assurance that a signed exchange is still valid, in the face of
revoked certificates and newly-discovered vulnerabilities. This
assurance can be bundled back into the signed exchange and forwarded
to another client, which won't have to re-fetch this validity
information for some period of time.
3.1. The Signature Header
The "Signature" header field conveys a single signature for an
exchange, accompanied by information about how to determine the
authority of and refresh that signature. Each signature directly
signs the exchange's headers and identifies one of those headers that
enforces the integrity of the exchange's payload.
The "Signature" header is a Structured Header as defined by
[I-D.ietf-httpbis-header-structure-02]. Its value MUST be a list
(Section 4.8 of [I-D.ietf-httpbis-header-structure-02]) of
parameterised labels (Section 4.4 of
[I-D.ietf-httpbis-header-structure-02]), and the list MUST contain
exactly one element.
Each parameterised label MUST have parameters named "sig",
"integrity", "validityUrl", "date", and "expires". Each
parameterised label MUST also have "certUrl" and "certSha256"
parameters. This specification gives no meaning to the label itself,
which can be used as a human-readable identifier for the signature
(see Section 3.1.2, Paragraph 1). The present parameters MUST have
the following values:
"sig" Binary content (Section 4.5 of
[I-D.ietf-httpbis-header-structure-02]) holding the signature of
most of these parameters and the exchange's headers.
"integrity" A string (Section 4.2 of
[I-D.ietf-httpbis-header-structure-02]) containing the lowercase
name of the response header field that guards the response
payload's integrity.
"certUrl" A string (Section 4.2 of
[I-D.ietf-httpbis-header-structure-02]) containing an absolute-URL
string [4] ([URL]).
"certSha256" Binary content (Section 4.5 of
[I-D.ietf-httpbis-header-structure-02]) holding the SHA-256 hash
of the first certificate found at "certUrl".
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"validityUrl" A string (Section 4.2 of
[I-D.ietf-httpbis-header-structure-02]) containing an absolute-URL
string [5] ([URL]).
"date" and "expires" An unsigned integer (Section 4.1 of
[I-D.ietf-httpbis-header-structure-02]) representing a Unix time.
The "certUrl" parameter is _not_ signed, so intermediates can update
it with a pointer to a cached version.
3.1.1. Examples
The following header is included in the response for an exchange with
effective request URI "https://example.com/resource.html". Newlines
are added for readability.
Signature:
sig1;
sig=*t7LoYw6vwL2FSZRNJPYdNdYjfZSQkaCQeqpBD1whcy/6AAamVJ2OryXoXv6ACVBQgPV13o5de9oOVcOGGMX9fsf2ve1UDw/ITpeimB7n3zcuDEePzIcPbUnicicN2yodZAfr5il7BBJTs8L+V2ZERI16nJfrOZOvUfhvuUaMDGQXx5StIj7XLiX7/caxPz5ctwglgVAwCmoVPhmYFLq391O+hEssHSk2xkY6r/D9V2cKMikBBOTZ+JFyrnS/f2B4li7YASIY0YX64ifCmCw97cQTngXax6Upoie44IAe+6JngOie9JlDgcMF3YZ1uxNGWl9VwlalSwWgi1YA9Ff7mQ;
integrity="mi";
validityUrl="https://example.com/resource.validity.1511128380";
certUrl="https://example.com/certs";
certSha256=*W7uB969dFW3Mb5ZefPS9Tq5ZbH5iSmOILpjv2qEArmI;
date=1511128380; expires=1511733180
The signatures uses a 2048-bit RSA certificate within
"https://example.com/".
It relies on the "MI" response header to guard the integrity of the
response payload.
The signature includes a "validityUrl" that includes the first time
the resource was seen. This allows multiple versions of a resource
at the same URL to be updated with new signatures, which allows
clients to avoid transferring extra data while the old versions don't
have known security bugs.
The certificate at "https://example.com/certs" has a "subjectAltName"
of "example.com", meaning that if it and its signature validate, the
exchange can be trusted as having an origin of
"https://example.com/".
3.1.2. Open Questions
[I-D.ietf-httpbis-header-structure-02] provides a way to parameterise
labels but not other supported types like binary content. If the
"Signature" header field is notionally a list of parameterised
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signatures, maybe we should add a "parameterised binary content"
type.
Should the certUrl and validityUrl be lists so that intermediates can
offer a cache without losing the original URLs? Putting lists in
dictionary fields is more complex than
[I-D.ietf-httpbis-header-structure-02] allows, so they're single
items for now.
3.2. CBOR representation of exchange headers
To sign an exchange's headers, they need to be serialized into a byte
string. Since intermediaries and distributors might rearrange, add,
or just reserialize headers, we can't use the literal bytes of the
headers as this serialization. Instead, this section defines a CBOR
representation that can be embedded into other CBOR, canonically
serialized (Section 3.4), and then signed.
The CBOR representation of an exchange "exchange"'s headers is the
CBOR ([RFC7049]) array with the following content:
1. The map mapping:
* The byte string ':method' to the byte string containing
"exchange"'s request's method.
* The byte string ':url' to the byte string containing
"exchange"'s request's effective request URI, which MUST be an
absolute-URL string [6] ([URL]).
* For each request header field in "exchange", the header
field's lowercase name as a byte string to the header field's
value as a byte string.
2. The map mapping:
* the byte string ':status' to the byte string containing
"exchange"'s response's 3-digit status code, and
* for each response header field in "exchange", the header
field's lowercase name as a byte string to the header field's
value as a byte string.
3.2.1. Example
Given the HTTP exchange:
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GET https://example.com/ HTTP/1.1
Accept: */*
HTTP/1.1 200
Content-Type: text/html
Content-Encoding: mi-sha256
MI: mi-sha256=20addcf7368837f616d549f035bf6784ea6d4bf4817a3736cd2fc7a763897fe3
<0x0000000000004000>
...
The cbor representation consists of the following item, represented
using the extended diagnostic notation from [I-D.ietf-cbor-cddl]
appendix G:
[
{
':url': 'https://example.com/'
':method': 'GET',
},
{
'mi': 'mi-sha256=20addcf7368837f616d549f035bf6784ea6d4bf4817a3736cd2fc7a763897fe3',
':status': '200',
'content-type': 'text/html'
'content-encoding': 'mi-sha256',
}
]
3.3. Loading a certificate chain
The resource at a signature's "certUrl" MUST contain a TLS 1.3
Certificate message (Section 4.4.2 of [I-D.ietf-tls-tls13])
containing X.509v3 certificates.
Parsing notes:
1. This resource MUST NOT include the 4-byte header that would
appear in a Handshake message.
2. Since this fetch is not in response to a CertificateRequest, the
certificate_request_context MUST be empty, and a non-empty value
MUST cause the parse to fail.
The client MUST ignore unknown or unexpected extensions.
Loading a "certUrl" takes a "forceFetch" flag. The client MUST:
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1. Let "raw-chain" be the result of fetching ([FETCH]) "certUrl".
If "forceFetch" is _not_ set, the fetch can be fulfilled from a
cache using normal HTTP semantics [RFC7234]. If this fetch
fails, return "invalid".
2. Let "certificate-chain" be the array of certificates and
properties produced by parsing "raw-chain" as the TLS Certificate
message as described above. If any of the requirements above
aren't satisfied, return "invalid". Note that this validation
requirement might be impractical to completely achieve due to
certificate validation implementations that don't enforce DER
encoding or other standard constraints.
3. Return "certificate-chain".
3.4. Canonical CBOR serialization
Within this specification, the canonical serialization of a CBOR item
uses the following rules derived from Section 3.9 of [RFC7049] with
erratum 4964 applied:
o Integers and the lengths of arrays, maps, and strings MUST use the
smallest possible encoding.
o Items MUST NOT be encoded with indefinite length.
o The keys in every map MUST be sorted in the bytewise lexicographic
order of their canonical encodings. For example, the following
keys are correctly sorted:
1. 10, encoded as 0A.
2. 100, encoded as 18 64.
3. -1, encoded as 20.
4. "z", encoded as 61 7A.
5. "aa", encoded as 62 61 61.
6. [100], encoded as 81 18 64.
7. [-1], encoded as 81 20.
8. false, encoded as F4.
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Note: this specification does not use floating point, tags, or other
more complex data types, so it doesn't need rules to canonicalize
those.
3.5. Signature validity
The client MUST parse the "Signature" header field as the list of
parameterised values (Section 4.8.1 of
[I-D.ietf-httpbis-header-structure-02]) described in Section 3.1. If
an error is thrown during this parsing or any of the requirements
described there aren't satisfied, the exchange has no valid
signatures. Otherwise, each member of this list represents a
signature with parameters.
The client MUST use the following algorithm to determine whether each
signature with parameters is invalid or potentially-valid for an
"exchange". Potentially-valid results include:
o The signed headers of the exchange so that higher-level protocols
can avoid relying on unsigned headers, and
o Either a certificate chain or a public key so that a higher-level
protocol can determine whether it's actually valid.
This algorithm accepts a "forceFetch" flag that avoids the cache when
fetching URLs.
1. Let "payload" be the payload body (Section 3.3 of [RFC7230]) of
"exchange". Note that the payload body is the message body with
any transfer encodings removed.
2. Let:
* "signature" be the signature (binary content in the
parameterised label's "sig" parameter).
* "integrity" be the signature's "integrity" parameter.
* "validityUrl" be the signature's "validityUrl" parameter.
* "certUrl" be the signature's "certUrl" parameter, if any.
* "certSha256" be the signature's "certSha256" parameter, if
any.
* "date" be the signature's "date" parameter, interpreted as a
Unix time.
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* "expires" be the signature's "expires" parameter, interpreted
as a Unix time.
3. If "integrity" names a header field other than "MI"
([I-D.thomson-http-mice]) or this header field is not present in
"exchange"'s response headers or which the client cannot use to
check the integrity of "payload" (for example, the header field
is new and hasn't been implemented yet), then return "invalid".
Clients MUST be able to check the integrity of "payload" using
the "MI" ([I-D.thomson-http-mice]) header field.
4. Set "publicKey" and "signing-alg" depending on which key fields
are present:
1. Assert: "certUrl" is present.
1. Let "certificate-chain" be the result of loading the
certificate chain at "certUrl" passing the "forceFetch"
flag (Section 3.3). If this returns "invalid", return
"invalid".
2. Let "main-certificate" be the first certificate in
"certificate-chain".
3. Set "publicKey" to "main-certificate"'s public key.
4. If "publicKey" is not a 2048-bit RSA public key, return
"invalid".
5. The client MUST define a partial function from public key
types to signing algorithms, and this function must at
the minimum include the following mappings:
RSA, 2048 bits: rsa_pss_rsae_sha256 or
rsa_pss_pss_sha256, as defined in Section 4.2.3 of
[I-D.ietf-tls-tls13], depending on which of the
rsaEncryption OID or RSASSA-PSS OID [RFC8017] is used.
Set "signing-alg" to the result of applying this function
to the type of "main-certificate"'s public key. If the
function is undefined on this input, return "invalid".
5. If "expires" is more than 7 days (604800 seconds) after "date",
return "invalid".
6. If the current time is before "date" or after "expires", return
"invalid".
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7. Let "message" be the concatenation of the following byte strings.
This matches the [I-D.ietf-tls-tls13] format to avoid cross-
protocol attacks when TLS certificates are used to sign
manifests.
1. A string that consists of octet 32 (0x20) repeated 64 times.
2. A context string: the ASCII encoding of "HTTP Exchange".
3. A single 0 byte which serves as a separator.
4. The bytes of the canonical CBOR serialization (Section 3.4)
of a CBOR map mapping:
1. If "certSha256" is set:
1. The text string "certSha256" to the byte string value
of "certSha256".
2. The text string "validityUrl" to the byte string value of
"validityUrl".
3. The text string "date" to the integer value of "date".
4. The text string "expires" to the integer value of
"expires".
5. The text string "headers" to the CBOR representation
(Section 3.2) of "exchange"'s headers.
8. If "certUrl" is present and the SHA-256 hash of "main-
certificate"'s "cert_data" is not equal to "certSha256" (whose
presence was checked when the "Signature" header field was
parsed), return "invalid".
Note that this intentionally differs from TLS 1.3, which signs
the entire certificate chain in its Certificate Verify
(Section 4.4.3 of [I-D.ietf-tls-tls13]), in order to allow
updating the stapled OCSP response without updating signatures at
the same time. Note that this difference doesn't matter for this
version of this draft since OCSP responses aren't checked.
9. If "signature" is a valid signature of "message" by "publicKey"
using "signing-alg", return "potentially-valid" with
"certificate-chain". Otherwise, return "invalid".
Note that the above algorithm can determine that an exchange's
headers are potentially-valid before the exchange's payload is
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received. Similarly, if "integrity" identifies a header field like
"MI" ([I-D.thomson-http-mice]) that can incrementally validate the
payload, early parts of the payload can be determined to be
potentially-valid before later parts of the payload. Higher-level
protocols MAY process parts of the exchange that have been determined
to be potentially-valid as soon as that determination is made but
MUST NOT process parts of the exchange that are not yet potentially-
valid. Similarly, as the higher-level protocol determines that parts
of the exchange are actually valid, the client MAY process those
parts of the exchange and MUST wait to process other parts of the
exchange until they too are determined to be valid.
3.5.1. Open Questions
Should the signed message use the TLS format (with an initial 64
spaces) even though these certificates can't be used in TLS servers?
3.6. Updating signature validity
Signatures are designed to expire a short time after they're signed,
so that revoked certificates and signed exchanges with known
vulnerabilities are distrusted promptly.
The "validityUrl" parameter (Paragraph 5) of the signatures provides
a way to fetch new signatures or learn where to fetch a complete
updated exchange.
Each version of a signed exchange SHOULD have its own validity URLs,
since each version needs different signatures and becomes obsolete at
different times.
The resource at a "validityUrl" is "validity data", a CBOR map
matching the following CDDL ([I-D.ietf-cbor-cddl]):
validity = {
? signatures: [ + bytes ]
? update: {
? size: uint,
}
]
The elements of the "signatures" array are parameterised labels
(Section 4.4 of [I-D.ietf-httpbis-header-structure-02]) meant to
replace the signatures within the "Signature" header field pointing
to this validity data. If the signed exchange contains a bug severe
enough that clients need to stop using the content, the "signatures"
array MUST NOT be present.
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If the the "update" map is present, that indicates that a new version
of the signed exchange is available at its effective request URI
(Section 5.5 of [RFC7230]) and can give an estimate of the size of
the updated exchange ("update.size"). If the signed exchange is
currently the most recent version, the "update" SHOULD NOT be
present.
If both the "signatures" and "update" fields are present, clients can
use the estimated size to decide whether to update the whole resource
or just its signatures.
3.6.1. Examples
For example, say a signed exchange whose URL is "https://example.com/
resource" has the following "Signature" header field (with line
breaks included and irrelevant fields omitted for ease of reading).
Signature:
sig1;
sig=*MEUCIQ...;
...
validityUrl="https://example.com/resource.validity.1511157180";
certUrl="https://example.com/oldcerts";
date=1511128380; expires=1511733180
At 2017-11-27 11:02 UTC, "sig1" has expired, so the client needs to
fetch "https://example.com/resource.validity.1511157180" (the
"validityUrl" of "sig1") to update that signatures. This URL might
contain:
{
"signatures": [
'sig1; '
'sig=*MEQCIC/I9Q+7BZFP6cSDsWx43pBAL0ujTbON/+7RwKVk+ba5AiB3FSFLZqpzmDJ0NumNwN04pqgJZE99fcK86UjkPbj4jw; '
'validityUrl="https://example.com/resource.validity.1511157180"; '
'integrity="mi"; '
'certUrl="https://example.com/newcerts"; '
'certSha256=*J/lEm9kNRODdCmINbvitpvdYKNQ+YgBj99DlYp4fEXw; '
'date=1511733180; expires=1512337980'
],
"update": {
"size": 5557452
}
}
This indicates that the client could fetch a newer version at
"https://example.com/resource" (the original URL of the exchange), or
that the validity period of the old version can be extended by
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replacing the original signature with the new signature provided.
The signature of the updated signed exchange would be:
Signature:
sig1;
sig=*MEQCIC...;
...
validityUrl="https://example.com/resource.validity.1511157180";
certUrl="https://example.com/newcerts";
date=1511733180; expires=1512337980
3.7. The Accept-Signature header
This section isn't implemented.
4. Cross-origin trust
To determine whether to trust a cross-origin exchange, the client
takes a "Signature" header field (Section 3.1) and the "exchange".
The client MUST parse the "Signature" header into a list of
signatures according to the instructions in Section 3.5, and run the
following algorithm for each signature, stopping at the first one
that returns "valid". If any signature returns "valid", return
"valid". Otherwise, return "invalid".
1. If the signature's "validityUrl" parameter (Paragraph 5) is not
same-origin [7] with "exchange"'s effective request URI
(Section 5.5 of [RFC7230]), return "invalid".
2. Use Section 3.5 to determine the signature's validity for
"exchange", getting "certificate-chain" back. If this returned
"invalid" or didn't return a certificate chain, return "invalid".
3. If "exchange"'s request method is not safe (Section 4.2.1 of
[RFC7231]) or not cacheable (Section 4.2.3 of [RFC7231]), return
"invalid".
4. If "exchange"'s headers contain a stateful header field, as
defined in Section 4.1, return "invalid".
5. Let "authority" be the host component of "exchange"'s effective
request URI.
6. Validate the "certificate-chain" using the following substeps.
If any of them fail, re-run Section 3.5 once over the signature
with the "forceFetch" flag set, and restart from step 2. If a
substep fails again, return "invalid".
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1. Use "certificate-chain" to validate that its first entry,
"main-certificate" is trusted as "authority"'s server
certificate ([RFC5280] and other undocumented conventions).
Let "path" be the path that was used from the "main-
certificate" to a trusted root, including the "main-
certificate" but excluding the root.
7. Return "valid".
4.1. Stateful header fields
As described in Section 6.1 of
[I-D.yasskin-http-origin-signed-responses], a publisher can cause
problems if they sign an exchange that includes private information.
There's no way for a client to be sure an exchange does or does not
include private information, but header fields that store or convey
stored state in the client are a good sign.
A stateful request header field informs the server of per-client
state. These include but are not limited to:
o "Authorization", [RFC7235]
o "Cookie", [RFC6265]
o "Cookie2", [RFC2965]
o "Proxy-Authorization", [RFC7235]
o "Sec-WebSocket-Key", [RFC6455]
A stateful response header field modifies state, including
authentication status, in the client. The HTTP cache is not
considered part of this state. These include but are not limited to:
o "Authentication-Control", [RFC8053]
o "Authentication-Info", [RFC7615]
o "Optional-WWW-Authenticate", [RFC8053]
o "Proxy-Authenticate", [RFC7235]
o "Proxy-Authentication-Info", [RFC7615]
o "Sec-WebSocket-Accept", [RFC6455]
o "Set-Cookie", [RFC6265]
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o "Set-Cookie2", [RFC2965]
o "SetProfile", [W3C.NOTE-OPS-OverHTTP]
o "WWW-Authenticate", [RFC7235]
4.2. Certificate Requirements
For this draft, no new X.509 extension is required.
5. Transferring a signed exchange
A signed exchange can be transferred in several ways, of which three
are described here.
5.1. Same-origin response
Receiving a Signature header as part of a normal HTTP exchange is not
implemented.
5.2. HTTP/2 extension for cross-origin Server Push
Cross origin push is not implemented.
5.3. application/signed-exchange format
To parse a resource with content type "application/signed-
exchange;v=b0", the client MUST run the following algorithm:
Read 3 bytes and interpret them as a big-endian integer
"headerLength".
If "headerLength" is larger than 524288 (512kB), parsing MUST fail.
Read "headerLength" bytes, and parse them as a CBOR item. If this
item isn't canonically encoded (Section 3.4) or doesn't match the
following CDDL, parsing MUST fail:
signed-exchange-header = [
{ ':method': bytes,
':url': bytes,
* bytes => bytes,
},
{ ':status': bytes,
'signature': bytes,
* bytes => bytes,
},
]
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The first element of the array is interpreted as the exchange's
request headers with lowercase names, with the request method in the
':method' key's value, and the effective request URI, which MUST be
an absolute-URL string [8] ([URL]), in the ':url' key's value.
The second element of the array is interpreted as the exchange's
response headers with lowercase names, with the 3-digit response
status code in the ':status' key's value.
If any header field name includes uppercase characters, parsing MUST
fail.
Pass the "Signature" response header and the exchange with that
header removed to the algorithm in Section 4. Fail if this returns
"invalid".
The remainder of the resource is the exchange's payload, encoded with
the "mi-sha256" content encoding ([I-D.thomson-http-mice]). If the
"mi-sha256" record length (the first 8 bytes of the payload) is
greater than 16kB, or if any of the integrity proofs fail validation,
parsing MUST fail.
6. Security considerations
All of the security considerations from Section 6 of
[I-D.yasskin-http-origin-signed-responses] apply.
In addition, because this draft does not check for certificate
revocation and allows signatures from certificates that can be used
in normal TLS servers with no defense against future-dated
signatures, clients MUST NOT trust signed exchanges as authoritative
for their claimed origin without some explicit opt-in by their user.
7. Privacy considerations
Normally, when a client fetches "https://o1.com/resource.js",
"o1.com" learns that the client is interested in the resource. If
"o1.com" signs "resource.js", "o2.com" serves it as "https://o2.com/
o1resource.js", and the client fetches it from there, then "o2.com"
learns that the client is interested, and if the client executes the
Javascript, that could also report the client's interest back to
"o1.com".
Often, "o2.com" already knew about the client's interest, because
it's the entity that directed the client to "o1resource.js", but
there may be cases where this leaks extra information.
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For non-executable resource types, a signed response can improve the
privacy situation by hiding the client's interest from the original
publisher.
To prevent network operators other than "o1.com" or "o2.com" from
learning which exchanges were read, clients SHOULD only load
exchanges fetched over a transport that's protected from
eavesdroppers. This can be difficult to determine when the exchange
is being loaded from local disk, but when the client itself requested
the exchange over a network it SHOULD require TLS
([I-D.ietf-tls-tls13]) or a successor transport layer, and MUST NOT
accept exchanges transferred over plain HTTP without TLS.
8. IANA considerations
This depends on the following IANA registration in
[I-D.yasskin-http-origin-signed-responses]:
o The "Signature" header field
This document also registers:
8.1. Internet Media Type application/signed-exchange
Type name: application
Subtype name: signed-exchange
Required parameters:
o v: A string denoting the version of the file format. ([RFC5234]
ABNF: "version = DIGIT/%x61-7A") The version defined in this
specification is "b0". When used with the "Accept" header field
(Section 5.3.1 of [RFC7231]), this parameter can be a comma
(,)-separated list of version strings. ([RFC5234] ABNF: "version-
list = version *( "," version )") The server is then expected to
reply with a resource using a particular version from that list.
Note: As this is a snapshot of a draft of
[I-D.yasskin-http-origin-signed-responses], it does not use a
simple integer to describe its version.
Optional parameters: N/A
Encoding considerations: binary
Security considerations: see Section 6.6 of
[I-D.yasskin-http-origin-signed-responses]
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Interoperability considerations: N/A
Published specification: This specification (see Section 5.3).
Applications that use this media type: N/A
Fragment identifier considerations: N/A
Additional information:
Deprecated alias names for this type: N/A
Magic number(s): 82 A?
File extension(s): .sxg
Macintosh file type code(s): N/A
Person and email address to contact for further information: See
Authors' Addresses section.
Intended usage: COMMON
Restrictions on usage: N/A
Author: See Authors' Addresses section.
Change controller: IESG
9. References
9.1. Normative References
[FETCH] WHATWG, "Fetch", April 2018,
.
[HTML] WHATWG, "HTML", April 2018,
.
[I-D.ietf-cbor-cddl]
Birkholz, H., Vigano, C., and C. Bormann, "Concise data
definition language (CDDL): a notational convention to
express CBOR data structures", draft-ietf-cbor-cddl-02
(work in progress), February 2018.
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[I-D.ietf-httpbis-header-structure-02]
Nottingham, M. and P. Kamp, "Structured Headers for HTTP",
draft-ietf-httpbis-header-structure-02 (work in progress),
November 2017, .
[I-D.ietf-tls-tls13]
Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", draft-ietf-tls-tls13-28 (work in progress),
March 2018.
[I-D.thomson-http-mice]
Thomson, M., "Merkle Integrity Content Encoding", draft-
thomson-http-mice-02 (work in progress), October 2016.
[I-D.yasskin-http-origin-signed-responses]
Yasskin, J., "Signed HTTP Exchanges", draft-yasskin-http-
origin-signed-responses-03 (work in progress), March 2018.
[POSIX] IEEE and The Open Group, "The Open Group Base
Specifications Issue 7", name IEEE, value 1003.1-2008,
2016 Edition, 2016,
.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, 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, DOI 10.17487/RFC5280, May 2008,
.
[RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049,
October 2013, .
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[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, DOI 10.17487/RFC7230, June 2014,
.
[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
DOI 10.17487/RFC7231, June 2014,
.
[RFC7234] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching",
RFC 7234, DOI 10.17487/RFC7234, June 2014,
.
[RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
DOI 10.17487/RFC7540, May 2015,
.
[RFC8017] Moriarty, K., Ed., Kaliski, B., Jonsson, J., and A. Rusch,
"PKCS #1: RSA Cryptography Specifications Version 2.2",
RFC 8017, DOI 10.17487/RFC8017, November 2016,
.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, .
[URL] WHATWG, "URL", April 2018, .
9.2. Informative References
[RFC2965] Kristol, D. and L. Montulli, "HTTP State Management
Mechanism", RFC 2965, DOI 10.17487/RFC2965, October 2000,
.
[RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265,
DOI 10.17487/RFC6265, April 2011,
.
[RFC6454] Barth, A., "The Web Origin Concept", RFC 6454,
DOI 10.17487/RFC6454, December 2011,
.
[RFC6455] Fette, I. and A. Melnikov, "The WebSocket Protocol",
RFC 6455, DOI 10.17487/RFC6455, December 2011,
.
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[RFC7235] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Authentication", RFC 7235,
DOI 10.17487/RFC7235, June 2014,
.
[RFC7615] Reschke, J., "HTTP Authentication-Info and Proxy-
Authentication-Info Response Header Fields", RFC 7615,
DOI 10.17487/RFC7615, September 2015,
.
[RFC8053] Oiwa, Y., Watanabe, H., Takagi, H., Maeda, K., Hayashi,
T., and Y. Ioku, "HTTP Authentication Extensions for
Interactive Clients", RFC 8053, DOI 10.17487/RFC8053,
January 2017, .
[W3C.NOTE-OPS-OverHTTP]
Hensley, P., Metral, M., Shardanand, U., Converse, D., and
M. Myers, "Implementation of OPS Over HTTP", W3C NOTE
NOTE-OPS-OverHTTP, June 1997.
9.3. URIs
[1] https://lists.w3.org/Archives/Public/ietf-http-wg/
[2] https://github.com/WICG/webpackage
[3] http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/
V1_chap04.html#tag_04_16
[4] https://url.spec.whatwg.org/#absolute-url-string
[5] https://url.spec.whatwg.org/#absolute-url-string
[6] https://url.spec.whatwg.org/#absolute-url-string
[7] https://html.spec.whatwg.org/multipage/origin.html#same-origin
[8] https://url.spec.whatwg.org/#absolute-url-string
Appendix A. Change Log
draft-00
Vs. [I-D.yasskin-http-origin-signed-responses]:
o Removed non-normative sections.
o Only 1 signature is supported.
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o Only 2048-bit RSA keys are supported.
o The certificate chain resource uses the TLS 1.3 Certificate
message format rather than a CBOR-based format.
o OCSP responses and SCTs are not checked.
o Certificates without the CanSignHttpExchanges extension are
allowed.
o The signature string starts with 64 0x20 octets like the TLS 1.3
signature format.
o The application/http-exchange+cbor format is replaced with a more
specialized application/signed-exchange format.
o Signed exchanges can only be transmitted using the application/
signed-exchange format, not HTTP/2 Push or plain HTTP request/
response pairs.
o Only the MI payload-integrity header is supported.
o The mi-sha256 encoding must have records <= 16kB.
o The Accept-Signature header isn't used.
o Require absolute URLs.
Appendix B. Acknowledgements
Authors' Addresses
Jeffrey Yasskin
Google
Email: jyasskin@chromium.org
Kouhei Ueno
Google
Email: kouhei@chromium.org
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