Internet DRAFT - draft-choi-pkix-ui
draft-choi-pkix-ui
Internet Draft B.H. Park
Document: draft-choi-pkix-ui-03.txt J.H. Yoon
Expires: December 8, 2005 I.K. Jeon
H.G. Lee
J.I. Lee
KISA
June, 2005
Required functions of User Interface
for the Internet X.509 Public Key Infrastructure
<draft-choi-pkix-ui-03.txt>
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Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
This document provides guidance to PKI client software developers on
what required functions are needed on user interface of PKI client
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software for human users to generate and verify digital signatures
easily and securely.
1. Introduction
Even though PKI is one of the most secure and influential
technologies to offer information security, most people say that it
is difficult to understand and utilize PKI technology because PKI
gives responsibilities for "human users"(users) to manage their
certificates and private keys.
General users of PKI technology generate their digital signature and
verify digital signatures by taking those responsibilities at the
application level. At this time, the users are usually directed by
user interface of PKI client software. Actually, they do not have to
know the whole mechanism of how PKI client software works, but they
just want to manage and use their certificates and private keys with
an aid of user interface keys and with any convenience.
However, businesses have so far neglected requirements for user
interface of PKI clientsoftware because most PKI technologies are
focusing on CA implementation. Consequently, the reason of people's
giving up accepting PKI technology is not difficulty of the very PKI
technology, but unkind user interface of PKI client software.
On the other hand, kind user interface should join in the following
processes of PKI client software when users generate and verity
digital signatures. First, user interface of PKI client software
shows users' certificates and private keys without users' involvement
in order that users can generate digital signatures with their
certificates and keys regardless of sorts of PKI applications.
Second, user interface gives access to users' certificate information
and enables users to manage their certificates without complexity of
user interface. Lastley, user interface uses the certificate of
users' trust anchor when the client software verifying digital
signatures. These processes can be implemented through core required
function that the PKI client software offters to users.
Thus, this document provides core required functions of user
interface when users generate and verify digital signatures so that
more users can utilize kind PKI technology. As for these functions
are certificate sharing function, import and export function,
certificate handling function, automatic update function, and
integrity verification function.
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2. Required functions
This section defines core required functions of user interface when
users generating and verifying digital signatures.
2.1 When generating digital signatures
Users use their own certificates and private keys provided by user
interface of PKI client software when generating digital signatures.
Thus, user interface should assist users to find and use their
certificates and private keys without any inconvenience when PKI
applications are operating. In other words, user interface should
provide the following compatibility and usability when users try to
generate digital signatures.
Compatibility shall be accomplished for using one certificate to many
PKI applications. Generally, PKI application such as the Internet
Banking or E-mail application defines the user's certificate and
private key location by their own way. Thereby, when using those
applications, users are at a loss whenever receiving a question where
their certificates are. Most users do not know the answer, and they
want to use different PKI programs with their own certificate without
answering the question. It comes true as a certificate sharing
function and transfer function that mainly aim for increasing
certificate compatibility, which benefits the user's convenience.
Usability shall be considered for a user who does not know about any
PKI knowledge to use PKI services by managing his or her certificates
easily. In this section, it specifies certificate handling function
of storage media and automatic updating function at the user
interface of PKI client software.
To meet both compatibility and usability when generating digital
signatures, user interface shall provide certificate sharing, import,
export, certificate handling, and automatic update funcion.
2.1.1 Certificate sharing function
User interface should allow multiple PKI applications to share users'
certificates and private keys for increasing compatibility in
different PKI applications. In addition, user interface should allow
users to utilize their own certificates and private keys without
inconvenience to search the certificates and keys. For these
requirements, there should be standardards for storing users'
certificates and private keys according to the users' operating
system and storage media, which is implemented through a certificate
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sharing function.
For example, a common storage location of a user's certificate and
private key in HARD DISK driver of different operating systems can be
assigned to be:
- MS Windows : C:Program Files/IETF/PKIX
- Linux/Unix : (User Account)/IETF/PKIX
- Mac OS X : (Hard disk label):Library/IETF/PKIX
For another example, in case of cryptographic tokens such as a
smardcad containing certificates and priviate keys, if the smartcards
follow a standard [PKCS#15], user interface of any application can
search the certificate with keys and present the contained
certificates and keys to users.
In these examples, a user can access to his or her own certificate
and key for generating digital signatures without answering the
question of where his or her certificate is. Note that it is supposed
that generating digital signatures are processed independently and
securely in the user's system.
Regarding as the user's certificate and private key, it may be stored
as a form of xxx.der or xxx.key, after creating a directory named by
DN. xxx naming is identically used for distinguishing between
digital signature and certificate distribution purpose.
In addition, the client software should define application
programming interface for accessing to various storage media such as
HARD DISK driver, SMARTCARD, FLOPPY disk, etc.
Format of the user's certificate in storage media may be encoded as
DER or PEM in order that the user interface can list all the
certificates in any storage media. For storage format of the private
key, it should use [PKCS5], which is a password based cryptographic
method. Afterward, it should be stored to a storage medium according
to [PKCS8].
2.1.2 Import and export function
The user interface shall provide import and export function to
support certificate's mobility according to [PKCS12]. This function
makes certificate and private key transfer to other PKI applications
so that the user can utilize his or her certificate and private key
in other PKI applications on the Internet X.509 Public Key
Infrastructure.
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2.1.3 Certificate handling function
User interface shall have at least three responsibilities for
handling the user's certificates;
- Certificate information notice
- Storage type selection
- Certificate management
Firstly, Certificate information notice at user interface is to
display certificate that was searched by client software so that user
can select the certificate to use it. At this point, important
information of certificate including subject name,expiration date,
and issuer name about certificate may be listed. In addition user
interface shall provide certificate information in detail if the
users want to receive the more information on their certificates.
Secondly, for selecting various storage types, storage type selection
in client software shall be made appropriately to display its storage
medium by categorization, which can be changed according to the
application's purpose.
On the certificate representation, a choice for storage media should
effectively provide for user to select the desired choice. In order
to do so, storage media are independently categorized by the nature
of storage media, which helps users to differentiate their own
storage easily from all the storage media. User interface may
consider including the followings:
- Hard disk
- Floppy disk
- USB
- Smartcard
- CD ROM
Lastly, the user interface shall contain certificate management
commands as followings;
- Integrity verification function of trust anchor : defined in
[2.2.1]
- Import and export : defined in [2.1.2]
- Certificate verification : when a user wants to know whether
his or her certificate is valid or not
- Private Key password change : when a user wants to change the
password of his or her private key
- Certificate deletion : when a user wants to delete his or her
certificate
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2.1.4 Automatic update function
The PKI client software must provide a secure method to update PKI
client software and trust anchor's certificate. This document defines
it as automatic update function, which makes user involvement
minimized. Note that there must be the integrity verification
function defined in 2.2.1 when the trust anchor's certificate is
updated automatically.
2.2 When verifying digital signatures
User interface of PKI client of PKI client software provides user
transparency when verifying digital signatures. Users do not have to
understand for the softwares how to make certificate chanis, verify
certificate signs, and validate the certificates. However, user
interface should provide users a way to confirm that trust anchor's
key is not compromised because security of trust anchor's key is
paramount for verification process of digital signatures. The way
should be implemented in the client software by integrity
verification function of trust anchor.
2.2.1 Integrity verification function of trust anchor
Users should acquire securely certificates of trust anchors which are
selected and trusted directly by users, which requires some out-of-
band steps.[CMP] This document describes integrity verification
function of trust anchor using user interface of PKI client softwares
as one of out-of-band steps.
First of all, PKI client software must be installed and upgraded with
a reliable and secure manner. This document does not refer to this
manner for PKI client software. Just after secure installation of PKI
client software, the client software will download the trust anchor's
certificate. At this point, the user interface of the client software
should offer integrity verification function of trust anchor in order
that users accept the trust anchor's certificate with reliability.
And also the user interface shall assist the users to make the
decision on whether or not the downloaded trust anchor's certificate
can be trusted. The user must accept the trust anchor's certificate
only if the trust anchor's certificate is verified through the
direction from the user interface.
The user interface shall help users to receive the trust anchor's
information for verifying out of band channel. The information must
not be received via more than two channels to reduce risks to be
attacked.
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For example when PKI client software acquires the trust anchor's
certificate after installation of client software, the user interface
can show the hash value of acquired trust anchor's certificate and
also direct how to acquire the trust anchor's information. The user
will acquire the hash value of the trust anchor's certificate through
at least two ways among face-to-face contacting, trust anchor's web
site, or cards by postal service, etc by the directions of the user
interface. Note that this example is sutible for the self-signed
certificate of trust anchor because it is possible not to compare the
hash values if the trust anchor's certificate is not self-signed.
In case that the trust anchor's certificate is updated, the client
software also must acquire updated trust anchor's certificate. At
this point, the client software can use its automatic upgrading
function of the trust anchor's certificate. And then user interface
must provide the same integrity verification function with an initial
installation of trust anchor's certificate.
In addition, the user interface should support integrity of trust
anchor's certificate with the verification function because there can
be malicious attack to the trust anchor's certificate after reliably
accepting the trust anchor's certificate when installing the client
software.
3. Security Considerations
Malicious attackers can access to a user's certificate and private
key because there is a common location for storing a certificate and
a private key according to a user's operating system and storage
media. However, it is supposed that there must be appropriate access
control for the user's system and storage media in this document.
4. Reference
4.1. Normative References
[RFC2119] S.Bradner, "Key words for use in RFCs to Indicate
Requirement Levels",RFC3467, March 1997
4.2 Informative References
[PKCS5] RSA Laboratories, PKCS#5 v2.0 "Password-Based
Cryptography Standard", RSA Data Security Inc., 1993
[PKCS8] RSA Laboratories, PKCS#8 v1.2 "Private Key Information
Syntax Standard", RSA Data Security Inc., 1993
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[PKCS12] RSA Laboratories, PKCS#12 v1.0 "Personal Key
Information Exchange Syntax Standard", RSA Data Security
Inc., 1993
[PKCS15] RSA Laboratories, PKCS#15 v1.1 "Cryptographic Token
Information Syntax Standard", RSA Data Security Inc.,
2000
[CMP] Adams, C. and Farrell, S., "Internet X.509 Public Key
Infrastructure Certificate Management Protocols",
RFC 2510, March 1999.
5. Authors' Address
Baehyo Park
Korea Information Security Agency
Phone: 2-405-5443
FAX : 2-405-5219
Email: parkbh@kisa.or.kr
Jaeho Yoon
Korea Information Security Agency
Phone: 2-405-5434
FAX : 2-405-5219
Email: jhyoon@kisa.or.kr
Inkyoung Jeon
Korea Information Security Agency
Phone: 2-405-5432
FAX : 2-405-5219
Email: inkyoung@kisa.or.kr
Hyangjin Lee
Korea Information Security Agency
Phone: 2-405-5446
FAX : 2-405-5219
Email: jiinii@kisa.or.kr
Jaeil Lee
Korea Information Security Agency
Phone: 2-405-5200
FAX : 2-405-5219
Email: jilee@kisa.or.kr
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