D. Gustafson
Future Foundation
M. Just
Entrust
Internet Draft M. Nystrom
Document: draft-ietf-sacred-framework-02.txt RSA Security
Expires: December 2001 July 2001
Securely Available Credentials - Credential Server Framework
Status of this Memo
This document is an Internet-Draft and is in full conformance
with all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
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Abstract
As the number, and more particularly the number of different
types, of devices connecting to the Internet increases, credential
mobility becomes an issue for IETF standardization. This draft
responds to the credential server framework requirements listed in
[SACRED]. It presents a strawman framework and outlines protocols
for securely available credentials.
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].
Please send comments on this document to the ietf-sacred@imc.org
mailing list.
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Table of Contents
STATUS OF THIS MEMO ............................................... 1
ABSTRACT .......................................................... 1
1 INTRODUCTION .................................................... 3
2 FUNCTIONAL OVERVIEW ............................................. 3
2.1 DEFINITIONS .................................................. 3
2.2 CREDENTIALS .................................................. 5
2.3 NETWORK ARCHITECTURE ......................................... 6
3 AUTHENTICATION METHODS .......................................... 7
3.1 STRONG PASSWORD PROTOCOLS .................................... 8
3.2 TLS AUTHENTICATION ........................................... 8
3.2.1 MUTUAL TLS AUTHENTICATION ................................. 8
3.2.2 TLS SERVER AUTHENTICATION ................................. 9
4 AUTHENTICATION OPTIONS .......................................... 9
4.1 CLIENT INITIALIZATION ........................................ 9
4.1.1 UNINITIALIZED CLIENT STATE ................................ 9
4.1.2 INITIALIZED CLIENT STATE .................................. 9
4.2 CLIENT AUTHENTICATION ....................................... 10
4.2.1 USER REGISTRATION ........................................ 10
4.2.2 CREDENTIAL DOWNLOAD ...................................... 10
4.2.3 POST CREDENTIAL DOWNLOAD OPERATIONS ...................... 11
5 PROTOCOL FRAMEWORK ............................................. 11
5.1 CREDENTIAL UPLOAD ........................................... 11
5.1.1 CREDENTIAL UPLOAD PROTOCOL SEQUENCE ...................... 12
5.2 CREDENTIAL DOWNLOAD ......................................... 12
5.2.1 CREDENTIAL DOWNLOAD PROTOCOL SEQUENCE .................... 13
5.3 CREDENTIAL REMOVAL .......................................... 14
5.3.1 CREDENTIAL REMOVAL PROTOCOL SEQUENCE ..................... 14
5.4 CREDENTIAL MANAGEMENT ....................................... 14
6 CREDENTIAL FORMATS ............................................. 15
6.1 PKCS #12 .................................................... 15
6.2 PKCS #15 .................................................... 16
7 OPEN ISSUES .................................................... 16
REFERENCES ....................................................... 17
AUTHOR'S ADDRESSES ............................................... 19
FULL COPYRIGHT STATEMENT ......................................... 19
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1 Introduction
Private credentials are used to support various Internet
protocols, e.g. S/MIME, IPSec, and TLS. In a number of
environments end users wish to use the same set of private
credentials on different end-user equipment. In a "typical"
desktop environment, the user already has many tools available to
allow import/export of these credentials. However, this is not
very practical. In addition, with some devices, especially
wireless and other more constrained devices, the tools required
simply do not exist.
This draft proposes a general framework for secure exchange of
user credentials and provides an outline of a protocol to meet
requirements stated in [SACRED].
2 Functional Overview
Requirements for Securely Available Credentials are fully
described in [SACRED]. These requirements assume that two
distinctly different network architectures will be supported to
exchange credentials between different end user systems:
a) Client/Server Credential Exchange
b) Peer-to-Peer Credential Exchange
This draft describes only the client/server architecture
framework. A separate framework draft may describe the peer-to-
peer architecture.
In all cases, adequate user authentication methods will be used to
ensure credentials are not divulged to unauthorized parties. As
well, adequate server authentication ensures that client
authentication information (see Section 2.1) is not compromised,
and so that the user retrieves their intended credentials (i.e. so
that a user isn't maliciously given an "older" set of credentials
to use).
2.1 Definitions
This section provides definitions for several terms or phrases
used throughout this draft.
client authentication information: information that is presented
by the client to a server to authenticate the client. This may
include a password token, a registration string that may have been
received out-of-band (and possibly used for initially registering
a roaming user) or data signed with a private signing key
credential belonging to the client (e.g. as part of TLS client
authentication).
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credentials: cryptographic objects and related data used to
support secure communications over the Internet. Credentials may
consist of public/private key pairs, symmetric keys, X.509 public
key certificates, attribute certificates, and/or application data.
Credentials are cryptographically protected for confidentiality
and integrity by encoding them in a standard format (e.g. PKCS#12
or PKCS#15). (See secured credentials below.)
passkey: a symmetric key, derived from a password.
password: a string of characters known only to a client and used
for the purposes of authenticating to a server and/or securing
credentials. A user may be required to remember more than one
password.
password token: a value derived from a password using a one-way
function that may be used by a client to authenticate to a server.
A password token may be derived from a password using a one-way
hash function, for example.
secured credentials: a set of one or more credentials that have
been cryptographically secured, e.g. encrypted/MACed with a
passkey. Secured credentials may be protected using more than one
layer of encryption, e.g. the credential is secured with a passkey
corresponding to a user's password and also by a key known only to
the server (the credential's stored form). Prior to network
transfer, the passkey-protected credential may be protected with
an additional encryption layer using a symmetric key chosen by the
Credential Server (e.g., the transmitted form).
strong password protocol: a protocol that authenticates clients to
servers securely, where the client need only memorize a small
secret (a password) and carries no other secret information, and
where the server carries a verifier (password token) which allows
it to authenticate the client. A shared secret is negotiated
between client and server and is used to protect data subsequently
exchanged.
Note the distinction between an "authentication password" and a
"credential password." An authentication password (and
corresponding token) may be used by a user to authenticate to a
Credential Server. A credential password may be used to generate a
passkey used to secure credentials. Although the same password may
be used to both authenticate and protect all credentials, it is
likely that different passkeys would be generated from this
password to protect credentials (i.e. because of different salt
values).
In addition, although it may be more convenient for a user to
remember only a single password, differing security policies (e.g.
password rules) between the credential server and the credential
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issuers may result in a user having to remember multiple
passwords.
2.2 Credentials
This document is concerned with the secure use of credentials in a
roaming or mobile environment. Credentials MAY be usable with any
end user device that can connect to the Internet, such as:
- desktop or laptop PC
- mobile phone
- personal digital assistant (PDA)
- etc.
The end user system may, optionally, store its credential
information on other special hardware devices that provide
additional portability and protection.
Since the credential usually contains sensitive information that
is known only to the credential holder, credentials MUST NOT be
sent in the clear during network transmission and SHOULD NOT be in
the clear when stored on an end user device such as a diskette or
hard drive. For this reason, a secured credential is defined.
Throughout this draft we assume that, at least from the point of
view of the protocol, a secured credential is an opaque (and at
least partially privacy and integrity protected) data object that
can be used by a network connected device. Once downloaded,
clients must be able to recover their credentials from this opaque
format.
At a minimum, all supported credential formats SHOULD provide
privacy and integrity protection for private keys, secret keys,
and other objects that must be protected from disclosure or
modification. Typically, these capabilities are part of the basic
credential format such that the credential (file) is protected
when stored on hard drives, flexible diskettes, etc.
Prior to network transmission, the full credential will be
protected with a second layer of encryption. This outer
encryption layer uses a negotiated, secret key that is shared
between sender and receiver only and provides an additional level
or protection from disclosure to unauthorized parties during
network transmission.
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2.3 Network Architecture
The network diagram below shows the components involved in the
sacred client/server framework.
+--------+ +------------+
| Client +-----------| Credential |
+--------+ 1 | Server |
\ +-----+------+
\ |
\ | 2
\ |
\ 3 +-----+------+
-----------| Credential |
| Store(s) |
+------------+
Client - The entity that wants to retrieve their credentials from
a credential server.
Credential Server - The server that downloads secure credentials
to and uploads them from the client. The server is
responsible for authenticating the client to ensure that
the secured credentials are exchanged only with an
appropriate end user. The credential server is
authenticated to the client to ensure that the client's
authentication information is not compromised and so
that the user can trust the credentials retrieved.
Credential Store - The repository for secured credentials. There
might be access control features but those generally
aren't sufficient in themselves for securing
credentials. The credential server may be capable of
splitting credentials across multiple credential stores
for redundancy or to provide additional levels of
protection for user credentials.
Protocol 1 - The protocol used to authenticate the client and
credential server, and download and upload user
credentials from a credential server.
Protocol 2 - The protocol used by the Credential Server to store
and retrieve user credentials (LDAP, LDAP/SSL, or
other).
Protocol 3 - The protocol used by the client to store and retrieve
user credentials from the credential store (LDAP,
LDAP/SSL, or other).
The high level design for protocol 1 is described by this
framework. Protocols 2 and 3 are closely related (but out of scope
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for this document) and could be implemented using standard
protocols, such as LDAP or secure LDAP, or other standard or
proprietary protocols. Note also that any administrator-
credential server protocols are assumed to be server vendor
specific and are not the subject of SACRED standardization efforts
at this time.
Clients are not precluded from exchanging credentials directly
with a credential store (or any other server of it's choosing).
However, mutual authentication with roaming users and a consistent
level of protection for credential data while stored on network
servers and while in transit is provided by the credential server.
Depending on credential server design, user credentials may flow
through the credential server to the credential store or directly
from the client to/from the credential store.
Also, users may upload their credentials to several credential
servers to obtain enhanced levels of availability. Coordination
(automatic replication) of user information or credential data
among several credential servers is currently beyond the scope of
this document.
3 Authentication Methods
Authentication is vitally important to ensure that credentials are
accepted from and delivered to the authorized end user only. If
an unsecured credential is delivered to some other party, the
credential may be more easily compromised. If a credential is
accepted from an unauthorized party, the user might be tricked
into using a credential which was substituted by an attacker (e.g.
an older credential for the user).
Ideally, the list of authentication methods should be open ended,
allowing new methods to be added as needs are identified and as
new methods become available. For all credentials, the user
authentication method/data is defined when a user is first
registered with the credential server and may be updated from time
to time thereafter by the authorized user.
To adequately protect user credentials from unauthorized
disclosure or modification in a roaming environment, all SACRED
authentication methods MUST provide protection for user
credentials in network environments where attackers might attempt
to exploit potential security vulnerabilities. See [SACRED]
Section 3.1, Vulnerabilities.
At a minimum, each SACRED authentication method SHOULD ensure
that:
- The server authenticates the client
- The client authenticates the server
- The client and server securely negotiate a cryptographically
strong, shared secret (a session key).
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- The exchange of one or more user credentials is protected using
this session key.
It is expected that even highly optimized SACRED protocols will
provide each of these logical functions (although the methods for
providing them may overlap substantially). Some existing
authentication protocols that might be used for this purpose
include:
- strong password
- TLS authentication
Section 4 gives some guidance as to the use of each authentication
method. The specifics of each supported authentication protocol is
(or will be) defined in a separate draft.
3.1 Strong Password Protocols
Strong password protocols such as those described in [RFC2945],
[BM92], [BM94], [PDM], and [SPEKE] will be used within SACRED
protocols. These strong password methods require that a user-
specific value (i.e. a password token) be configured within the
server. This verifier value can only be calculated by a party who
knows the password (the user) and must be securely delivered to
the server at a time when the user establishes a relationship with
the server. At connect time, messages are exchanged between the
two parties and complementary algorithms are used to compute a
shared common value known only to the legitimate user and the
server. In all cases, both parties derive a strong (symmetric)
key that may be used to secure subsequent communications between
the two parties.
For the purpose of initial registration a secret shared out-of-
band between the user and the Credential Server may be used to
strongly authenticate both parties.
3.2 TLS Authentication
TLS authentication may either be mutual between the client and
server or unilateral where only the server is authenticated to the
client. These options are indicated in the following two
subsections. In either case, authentication of the server
requires that the user possesses at least one trusted root (in
addition to their password).
3.2.1 Mutual TLS Authentication
Following server authentication, the server MAY request TLS client
authentication. If the client is currently configured with a
suitable certificate, this operation can be used to authenticate
the client. TLS client authentication is not possible whenever the
client device has no such credential. Note also the requirement
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that the server must be able to successfully validate the user's
certificate.
3.2.2 TLS Server Authentication
In the case that a client does not have a certificate with which
to mutually authenticate with the server, then subsequent to a
server authentication, the client may authenticate with a password
token. This is a viable option whenever the client certificate
cannot be validated by the Credential Server.
4 Authentication Options
The choice of authentication mechanism depends very much upon the
client state, and in particular, what information is available to
them. This section provides some guidance as to what general
authentication methods might be more appropriate given the
client's environment and operation that they intend to perform.
4.1 Client initialization
Authentication of the server, by the client depends on whether the
client possesses any trusted roots or not. We distinguish such
client state as follows.
4.1.1 Uninitialized client state
In order to use http/TLS transport protocol, client software must
be configured with one or more root certificates. Root
certificates, sometimes called self-signed or self-issued
certificates must be protected by some external means (e.g. other
than the certificate's digital signature) at all times.
Typically, each secure application installs one or more root
certificates during the software installation process then
protects them using application-specific methods.
Prior to client initialization, strong password authentication can
be used to authenticate client and server and protect user
credential(s) while in transit. Once received, client software
can install and configure root certificates, client credentials,
and other data as appropriate.
4.1.2 Initialized client state
Once root certificates have been installed, http/TLS capability is
available and the client device can utilize a wider range of
authentication and credential exchange options to upload
credentials, download additional credentials, etc.
Several combinations of strong password authentication and
http/TLS (see section 4.2 for details) can be used to mutually
authenticate client and server then exchange credentials.
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4.2 Client authentication
The authentication method used by the client to the server depends
on the information currently available to the client. It is
helpful to distinguish based on the operation that is being
performed. There are essentially three different macro-level
operations that may be performed by a client interacting with the
credential server. This classification of operations is given in
the following subsections. Note that in all cases, the user may
either be "self registered" or may be registered through the
facilities of an administrative process or method that is
associated with the credential server. The administrative process
or method operates as a user with special create/update privilege.
4.2.1 User Registration
A user registering with a credential server will likely currently
possess credentials that may be used to authenticate to the
Credential Server. In this case, mutual TLS authentication (see
Section 3.2.1) may be used (provided the user has been initialized
- see Section 4.1.2). However, the use of the client certificate
also requires that the Credential Server is able to establish
trust in this certificate.
Alternatively, a user might register using a secret shared out-of-
band with the credential server, and used in a strong-password-
based protocol (see Section 3.1). This alternative supports an
uninitialized user (see Section 4.1.1) but requires an out-of-band
sharing.
In the case that identification of the user is not required as
part of their registration, an initialized user (see Section
4.1.2) may upload the appropriate registration information to the
Credential Server over a server-authenticated TLS session (see
Section 3.2.2).
4.2.2 Credential Download
An uninitialized user (see Section 4.2.1) not currently possessing
any certificate information may use a strong-password-based
protocol (see Section 3.1) as authentication for downloading their
credentials.
Alternatively, an initialized user (see Section 4.2.2) may use a
server authenticated session and user password to authenticate to
the Credential Server (see Section 3.2.2).
An initialized user already possessing a certificate that is
verifiable by the Credential Server may establish a mutually
authenticated TLS session (see Section 3.2.1) prior to download.
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4.2.3 Post Credential Download Operations
Once a client has retrieved their credentials, an initialized
client (see Section 4.2.2) may use mutual TLS authentication (see
Section 3.2.1) to perform any subsequent operations (so long as
the credential server is able to determine the validity of the
user certificate).
Alternatively, an initialized user (see Section 4.2.2) may use a
server authenticated session and user password to authenticate to
the Credential Server (see Section 3.2.2).
An uninitialized user (see Section 4.2.1) may use a strong-
password-based protocol (see Section 3.1) as authentication for
any post credential download operations.
5 Protocol Framework
This section provides a high level description of client/server
protocols that can be used to exchange and manage SACRED
credentials.
The client/server credential exchange protocol is based on three
basic and abstract operations; "GET", "PUT", and "DELETE".
Access to credentials is based on a user supplying at least a user
name and appropriate client authentication information. Successful
authentication by the user allows access to the secured
credentials corresponding to the authenticate user name. For each
user name, different "handles" may be assigned to different
secured credentials, e.g. there may be one handle for "financial"
and one for "healthcare" credentials. If a user would like to have
a distinct (authentication) password in order to obtain different
secured credentials, then they may register credentials under
distinct user names.
5.1 Credential Upload
The purposes of a credential upload capability are:
- to allow a client to register new credentials with a
credential server, and
- to allow a client to modify currently stored credentials with
new credentials, e.g. credentials that may have been updated by the
client using appropriate key management software.
The framework for credential upload (PUT operation) is:
- The client and server establish a mutually authenticated
session and negotiate a shared secret.
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- The client will then issue a PUT message that contains the
upload credential and the following data fields:
- Credential Format ID and Data: The user's protected
credential and a format identifier that is needed to parse the
credential after it has been downloaded.
- Credential Handle: The handle or alias associated with the
credential.
The credential server's response to this PUT message SHOULD
contain an identifier of the (version of the) credential, which
MAY be used to optimize later downloads.
5.1.1 Credential Upload Protocol Sequence
The following gives an example of a "credential upload" protocol
sequence:
client server
------- -------
< connect > -->
<--- mutual authentication --->
< Cred-1 > -->
<-- < Cred-1 URL, ID >
< Cred-2 > -->
<-- < Cred-2 URL, ID >
...
< done > -->
<-- OK (+ connection dropped)
where,
The <mutual authentication> protocol exchange is dependent upon
the authentication method used. In any case, its end result is to
authenticate the client to the server and server to the client,
and establish a symmetric key shared between the two parties.
Cred-x URL is a locator that can be used to access the secured
credential for download.
Cred-x ID is a indicator that may be used for conditional download
(e.g. http/1.1 "if modified-since").
5.2 Credential Download
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Roaming clients can download their credentials at any time after
they have been uploaded to the server.
The framework for a credential download (GET operation) is:
- The server SHOULD be authenticated to the client
- the user MUST be authenticated (by the server) using a method-
dependent protocol sequence
- a GET request for the credential download is issued
- the response contains the credential and format identifier
The specific user credential being requested may be identified in
the message sent to the credential server. If successful, the
response MUST contain the requested credential data element
(format ID and data) as defined above. In the case that a
credential handle is not specified, all credentials associated
with the given user name may be returned.
Optionally, the user agent MAY include a previously obtained
fingerprint (see above) to determine whether a download is
necessary. If the server finds that the credential has not been
modified, it MAY indicate this in its response.
5.2.1 Credential Download Protocol Sequence
The following gives an example of a "credential download" protocol
sequence:
client server
------- --------
< connect > -->
<--- mutual authentication --->
< GET Cred-1 URL
[Fingerprint]> -->
<-- < GET response 1 (Cred-1) >
< GET Cred-2 URL
[Fingerprint]> -->
<-- < GET response 2 (Cred-2) >
...
< done > -->
<-- OK (+ connection dropped)
where,
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Cred-x URL is a locator for a specific credential. Each download
request may be conditional.
Fingerprint is an optional value that may be used to indicate that
a specific version or revision level of Cred-x is already
available to the client.
5.3 Credential Removal
The framework for credential removal (DELETE operation) is:
- the credential server MUST be authenticated, that is only TLS
ciphersuites providing strong confidentiality and server
authentication MAY be used in the case that TLS authentication is
used
- the user MUST be authenticated (by the server) using a method-
dependent protocol sequence
- the user then sends a DELETE message that contains the
credential Identifier indicating which credential to remove.
5.3.1 Credential Removal Protocol Sequence
The following gives an example of a "credential removal" protocol
sequence:
client server
------- --------
< connect > -->
<-------- mutual authentication -------->
< DEL Cred-1 URL > -->
<-- < Cred-1 deleted >
< DEL Cred-2 URL > -->
<-- < Cred-2 deleted >
...
< done > -->
<-- OK (+ connection dropped)
where,
Cred-x URL is a locator for a specific credential.
5.4 Credential Management
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Note that the three basic operations defined above (GET, PUT,
DELETE) can be used to perform the necessary management
operations:
- create a new credential on the server
- update an existing credential
- delete an existing credential
These basic operations might also be used to construct more
complex operations such as registration, de-registration, change-
password, or list-credentials.
The credential is an opaque (encrypted) data object with user
defined format. Section 6 mentions some possible credential
formats. However, no credential format is excluded in this memo.
There is no restriction on the data that may be included in a user
credential or the credential storage format seen by the server.
6 Credential Formats
To ensure that credentials created on, and uploaded from, one
device can be downloaded and used on any other device, there is a
need to define a single "mandatory to implement" credential format
that must be supported by all conforming client and server
implementations.
Other optional credential formats may also be supported. Each
credential format must provide adequate privacy protection for
user credentials when they are stored on flexible diskettes, hard
disks, etc. This section describes two possible candidate
formats, both (believed to be) unencumbered, and both engineered
for widespread use and able to carry and store credential
information with adequate privacy protection.
Thoughout this document, the credential is treated as an opaque
(encrypted) object and, as such, the credential format does not
affect the basic credential exchange protocol. Additional
credential formats may be defined for use with specific
(compatible) client devices as needed. Whenever needed, adequate
care should be taken to ensure that similar levels of privacy
protection are afforded by each credential format used.
6.1 PKCS #12
PKCS #12 [PKCS12] provides a transfer syntax for personal identity
information, including private keys, certificates, and
miscellaneous secrets. It is widely used and would therefore
constitute a natural choice for a SACRED credential format.
PKCS #12 is capable of providing a highly flexible, secure
credential format that may contain any number of public/private
key pairs, PKCS #8 shrouded key pairs, EE or CA certificates, and
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miscellaneous secrets. The entire credential is integrity
protected using a digital signature or SHA-1 HMAC. It is expected
that sensitive Credential objects will be privacy protected using
the password-based-encryption option defined in PKCS #12.
6.2 PKCS #15
PKCS #15 [PKCS15] specifies a file and directory format for
storing security-related information on cryptographic tokens
(which are defined as portable devices capable of storing
persistent data). PKCS #15 has seen its main use as a smart card
application where it facilitates interoperability and credential
portability. Among things speaking in favor of PKCS #15 are:
- Capable of carrying more certificate types (e.g. WAP WTLS [WTLS]
certificates]
- Capable of carrying "raw" public keys
- Standardized set of secret key types
Among things speaking against PKCS #15 are:
- The software token format has recently been defined and is
not widely used
7 Open Issues
This document is intended to foster further discussion of the
framework and protocols that might be used to support credential
mobility. Some open issues that remain are:
- Flexibility: Users should be able to access their credentials
from any device using any supported authentication method
8 Security Considerations
The Security Considerations section of [SACRED] applies to this
memo as well. In particular, and as mentioned in [SACRED], mobile
credentials will never be as secure nor as tamper-resistant as
hardware solutions. However, reasonable security may be
accomplished through some relatively simple means, as outlined
above and in [SACRED].
Some additional security considerations are:
- For uploads, if the user is not authenticated, the server
MUST make sure not to accidentally overwrite another user's
credentials.
- For downloads, if the server is not authenticated, the user
MUST be made aware of risks associated with this fact. For example,
the user may unknowingly reveal information regarding their
authentication password (in the case a password token is supplied
Gustafson, Nystrom, & Just [page 16]
Securely Available Credentials - July 2001
Credential Server Framework
over a server authenticated TLS channel). As well, a user might be
unknowingly given an old credential to use.
- Using any password-based techniques, user passwords need
never be stored "in the clear" on credential servers.
- Credential servers SHOULD provide mechanisms to protect
against remote dictionary attacks on user passwords, either by
repeated access attempts to a single user account or by testing many
user accounts using the exact same password. Since such mechanisms
may include temporarily locking user accounts, adequate status
reporting provisions should be included in affected SACRED protocols.
- Clients SHOULD provide mechanisms to protect against a user
inadvertently entering her password in the "user name" field or
otherwise causing her password to be sent "in the clear" over the
network.
- The effective level of protection afforded user passwords, no
matter how they are transformed by one-way hash operations, etc. is
directly proportional to how well passwords (e.g., password
verifiers) are protected by the server.
- To ensure the integrity of mutual authentication and
transaction privacy, credential servers SHOULD protect "password
verifiers" with the same rigor that they protect their private key.
- It is expected that credential users will make use of
physical security or additional encryption layers (or both) to
further protect their locally stored credentials, whenever
appropriate.
References
[SACRED] Arsenault, A., Farrell, S., "Securely Available
Credentials - Requirements", Internet Draft < draft-
sacred-reqs-03.txt>, June 2001.
[PKCS12] "PKCS 12 v1.0: Personal Information Exchange Syntax",
RSA Laboratories, June 24, 1999
[PKCS15] "PKCS #15 v1.1: Cryptographic Token Information Syntax
Standard", RSA Laboratories, June 2000.
[RFC2026] Bradner, S., "The Internet Standards Process - Revision
3", BCP 9, RFC 2026, October 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997.
[RFC2246] Dierks, T., Allen, C., "The TLS Protocol Version 1.0,"
RFC 2246, January 1999.
Gustafson, Nystrom, & Just [page 17]
Securely Available Credentials - July 2001
Credential Server Framework
[RFC2289] Haller, N., Metz, P., Nesser, P., & Straw, M., "A One-
Time Password System", RFC 2289.
[RFC2444] Newman, C., "The One-Time-Password SASL Mechanism", RFC
2444, November 1997.
[RFC2616] R. Fielding, J. Gettys, J. Mogul,, H. Frysyk, L.
Masinter, M. Leach, T. Berners-Lee, "Hypertext Transfer
Protocol - HTTP/1.1", RFC 2616.
[RFC2945] Wu, T., "The SRP Authentication and Key Exchange
System", RFC 2945, September 2000.
[PDM] Perlman, R., Kaufman, C., Rescorla, E. "Strong Password-
Based Credentials Download Using Pseudorandom Moduli
<draft-perlman-strong-cred-00.txt>, December 2000.
[SPEKE] Jablon, D., "Strong Password-Only Authenticated Key
Exchange", September 1996
[BM92] S. Bellovin and M. Merritt, "Encrypted Key Exchange:
Password-based protocols secure against dictionary
attacks", Proceedings of the IEEE Symposium on Research
in Security and Privacy, May 1992.
[BM94] S. Bellovin and M. Merritt, "Augmented Encrypted Key
Exchange: a Password-Based Protocol Secure Against
Dictionary Attacks and Password File Compromise, ATT
Labs Technical Report, 1994.
[FK00] Ford, W., Kaliski, B., "Server-Assisted Generation of a
Strong Secret from a Password", June 2000.
[WTLS] WAP, "Wireless Application Protocol - Wireless Transport
Layer Security Specification," Approved version, 18-Feb-
2000.
Gustafson, Nystrom, & Just [page 18]
Securely Available Credentials - July 2001
Credential Server Framework
Author's Addresses
Dale Gustafson
Future Foundation, Inc.
450 Pillsbury Center
200 South Sixth Street
Minneapolis, MN 55402 Phone: +1 651-452-9033
USA Email: dale.gustafson@bpsi.net
Mike Just
Entrust, Inc.
1000 Innovation Drive
Ottawa, ON K2K 3E7 Phone: +1 613-270-3685
Canada Email: mike.just@entrust.com
Magnus Nystrom
RSA Security
Box 10704
121 29 Stockholm Phone: +46 8 725 0900
Sweden Email: magnus@rsasecurity.com
Full Copyright Statement
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Gustafson, Nystrom, & Just [page 19]
