INTERNET-DRAFT Editor: Stephen Farrell
expires in six months Baltimore Technologies
January 2002
Securely Available Credentials Protocol
<draft-ietf-sacred-protocol-bss-01.txt>
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
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts. 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."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
Abstract
This document describes an SRP-based protocol for securely available
credentials.
Discussion of this draft is taking place on the SACRED mailing list
of the IETF SACRED working group (see http://www.imc.org/ietf-sacred
for subscription information).
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Table Of Contents
Status of this Memo.............................................1
Abstract........................................................1
Table Of Contents...............................................2
1. Introduction.................................................2
2. The protocol.................................................3
3. Message Formats..............................................6
4. BEEP Profile for SACRED......................................8
5. IANA Considerations.........................................11
6. Security Considerations.....................................11
References.....................................................13
Acknowledgements...............................................13
Editor's Address...............................................14
Full Copyright Statement.......................................14
Appendix A: XML Schema.........................................14
Appendix B: DTD................................................17
Appendix C: An Example of Tuning with BEEP.....................18
Appendix D: Provision SACRED using other Protocols.............19
Appendix E: Changes & Open Issues..............................20
1. Introduction
<<Open issues/editorial notes are in brackets, like this.>>
We describe a protocol whereby a user can acquire cryptographic
credentials (e.g., private keys, PKCS#15 structures) from a
workstation which has locally trusted software installed, but with
no user-specific configuration. This is somewhat less secure than a
smart card, but can be used until smart cards and smart card readers
on workstations become ubiquitous, and can be useful even after
smart cards are ubiquitous, as a backup strategy when a user's smart
card is lost or malfunctioning.
The security of the protocol is based on [SRP]. The protocol uses
[BEEP] for its exchange model and the [SASL] SRP mechanism [SASL-
SRP] to encapsulate the SRP exchanges. The payloads consist of a set
of XML messages defined here. The protocol sets out to meet the
requirements in [REQS].
We assume the only authentication information available to the user
is a username and password.
Many user-chosen passwords are vulnerable to dictionary attacks. So
this protocol is designed to give no information with which an
attacker can acquire information for launching a dictionary attack,
whether by eavesdropping or by impersonating either the client or
server.
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The protocol also allows a user to create or delete an account,
change her account password and/or credentials and upload the new
values to the server. The protocol ensures that only someone that
knew the old account password is able to modify the credentials as
stored on the credential server. The protocol does not preclude
configuring a server to disallow some operations (e.g. credential
upload) from some users. The account management operations as a
whole are OPTIONAL to implement for both credential servers and
clients.
Note that there are potentially two "passwords" involved when using
this protocol - the first used to authenticate the user to the
credential server, and the second to decrypt (parts of) the
credential following a download operation. Where the context
requires it, we refer to the former as the account password and the
latter as the credential password.
2. The protocol
This section defines the account management and "run-time"
operations for the SACRED protocol.
2.1 Account management operations
These operations MAY be implemented, that is, they are OPTIONAL.
2.1.1 Information Request
This operation requires no authentication.
The purpose of this operation is to provide to the client the values
required for account creation. The client sends an InfoRequest
message and the server responds with an InfoResponse message.
2.1.2 Create Account
This operation requires TLS server authentication.
The purpose of this operation is to setup a new account on the
server. A "new" account consists of the username and account
password verifier with no associated credentials. In order to
associate a credential with an account, the client MUST carry out
the credential upload operation, which requires SRP authentication.
The client sends a CreateAccountRequest and the server responds with
an error or acknowledgement message.
2.1.3 Remove Account
The client sends a RemoveAccountRequest message to the server. The
server MUST delete all information relating to the account and
respond with an error or acknowledgement message.
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2.1.4 Account Password change
The client sends a PWChangeRequest message to the server. The server
changes the account's password verifier value and responds an error
or acknowledgement message.
2.2 "Run-time" operations
These operations MUST be supported by all conformant
implementations.
2.2.1 Credential Upload
The client sends an UploadRequest message to the server. The server
responds with an error or acknowledgement message.
If a credential with the same credential selector field (a
"matching" credential) already exists for the account, then that
credential is replaced with the new credential from the
UploadRequest. If the new credential from the UploadRequest contains
no Payload field then the "matching" credential is deleted.
2.2.2 Credential Download
The client sends a DownloadRequest message to the server. The server
responds with a DownloadResponse message.
2.3 Session security
Six SACRED operations are defined above. In this section we specify
the requirements for security for each of the operations (where
supported). We first define the options and then specify which
options MUST be supported for which operations.
- NONE means what it says - no authentication is required
- sTLS means that the BEEP session MUST be "tuned" for server-
authenticated TLS [TLS].
- cTLS means that the BEEP session MUST be "tuned" for mutually-
authenticated TLS.
- SRP means that the BEEP session MUST be "tuned" for SASL-SRP; MUST
use the SASL security layer with all three security services
(confidentiality, replay protection and integrity); MUST set the
authorization identity to the same value as the authentication
identity and MUST use the mandatory-to-implement algorithms from
[SASL-SRP].
<<There were three authorization identity options discussed on the
list but we didn't get a clear concensus. They were 1) as above, 2)
clients should omit the field & allow server to do what it likes,
allow client to specify an authorization id and say server MUST
handle that (possibly barfing if != authentication id).>>
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Note: "Tuned" is a piece of BEEP terminology that roughly means
"have security turned on as part of the channel initialization".
More properly we could refer to "tuning BEEP for authentication and
privacy". Appendix C gives an example of how tuning works.
The mandatory-to-implement TLS cipher-suite for SACRED is:
TLS_RSA_WITH_3DES_EDE_CBC_SHA. This MUST be used for both sTLS and
cTLS cases.
Where both SRP and cTLS security are supported for the same account,
the server MUST maintain some (secure) mapping between the SRP
authentication identity and the client certificate involved. How
this is done is out of scope.
Security required for each SACRED operation:
Operation Security REQUIRED
--------- -----------------
Information request NONE
Create account sTLS
Remove account SRP or cTLS
Account password change SRP or cTLS
Credential upload SRP or cTLS
Credential download SRP or cTLS
Where there is a choice (i.e. either SRP or cTLS allowed), servers
MUST support both options and clients MUST support at least one of
the options.
<<Open issue: MUST a server that only supports up/downloads support
cTLS as well as SRP, or is SRP-alone sufficient for this case?>>
2.4 Session management
<<The need for this entire section has been questioned. Should it be
more BEEP-like, deleted, s/MUST/SHOULD/ on dropping the
connection?>>
Once the BEEP session is appropriately tuned for security, the
client can issue one SACRED request. Once the response to this
request has been sent the server MUST drop the connection. If a
client wishes to combine operations, (e.g. download and then modify
credentials), the client software MAY temporarily store e.g. the
account password, but MUST re-authenticate each time it connects to
the server.
2.5 Handling multiple credentials for an account
When more than one credential is stored under a single account, the
client can select a single credential using the optional credential
selector string.
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There is no concept of a "default credential" - all credentials MUST
have an associated selector unique for that account. The selector
is REQUIRED for upload requests and OPTIONAL for download requests.
If the selector is omitted in a download request it MUST be
interpreted as a request for all the stored credentials.
It is an error to have more than one credential stored under the
same account where both have the same credential selector string.
<<Is an empty selector string allowed? (i.e. "") Probably good to
allow that and for it to differ from a missing selector string
(meaning "all") in download requests.>>
3. Message Formats
This section describes the message formats used, which are based on
XML. Appendices A & B provide schema and DTD for these elements.
The approach taken here is to define SACRED elements that are
compatible with the elements used in [XKMS] and [XMLDSIG], so that
an implementation of this protocol can easily also support XKMS, and
vice versa.
It is also intended that other SACRED protocol instances (e.g. using
a different authentication scheme, credential format or transport
protocol) could re-use many of the definitions here.
3.1 Common fields
The type "ds:CryptoBinary" (inherited from [XMLDSIG]) is used for
almost all binary values. The value in such elements MUST be the
base64 encoding of the binary value in network byte order. See
[XMLDSIG] for further details and example. The exception to this is
the "salt" field, which is of type base64Binary instead. The reason
for this is that leading zeros are stripped from ds:CryptoBinary,
which is correct in most cases, but since the salt is a direct input
to a hash function, leading zeros are significant and so have to be
preserved.
All messages sent to the server MAY contain ProcessInfo values. This
field MAY be used by other specifications or for vendor extensions.
For example, a server might require clients to include a phone
number in this field. The information response message contains a
list of the types of ProcessInfo that the server supports. This
extensibility scheme is the same as that used in [XKMS] and [XBULK].
Where no specific response message is defined for an operation(e.g.
for PWChangeRequest) then the BEEP "ok" or "error" messages are used
to indicate success or failure.
All of the response messages defined here MAY contain a Status
string, containing a value intended for human consumption. In a BEEP
"error" message the status string is the content of the element.
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3.2 Credential Format
A number of messages involve the Credential element. It has the
following fields (all optional fields may occur exactly zero or one
times unless otherwise stated):
- CredentialSelector contains a string by which this particular
credential (for this account) can be identified.
- LastModified specifies the time at which this credential was last
changed. (Note: the server SHOULD ensure this value is reasonably
accurate.)
- TimeToLive (optional) is a hint which clients SHOULD honor, which
specifies the number of seconds for which the downloaded
credential is to be usable.
- ProcessInfo (optional) MAY contain any (typed) information that
the server is intended to process. If the server doesn't support
any of the ProcessInfo data, it MAY ignore that data.
- ClientInfo (optional) MAY contain any (typed) information that the
client is intended to process, but which the server MUST ignore.
If the client doesn't support any of the ClientInfo data, it MAY
ignore that data (e.g. if the ClientInfo is device specific).
- CredentialElements contains either a ds:KeyInfo or some other form
of credential. Implementations MUST support the pkcs#15 form of
ds:KeyInfo defined below (the SacredPKCS15 element).
The LastModified value can also be of use in detecting conflicts.
For example, download to platform A, download to platform B, update
from B, update from A. The server could detect a conflict on the
second upload.
3.3 InfoRequest
There is no content to this message.
3.4 InfoResponse
Contains the SRP settings for the server and the list of supported
ProcessInfo types.
3.5 CreateAccountRequest
This message contains the account name (e.g. username), the salt and
the password verifier for the account.
3.6 RemoveAccountRequest
There is no content to this message.
3.7 PWChangeRequest
This message contains a new salt and password verifier for the
account.
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3.8 DownloadRequest
This message MAY contain the credential selector string for the
credential.
3.9 DownloadResponse
This message contains the credential.
3.10 UploadRequest
The message contains the previous value for the credential's
LastModified field and the new credential.
Note: A server SHOULD ensure that the LastModified value in the new
credential is reasonably accurate. If it isn't then the server
SHOULD respond with an error message in which case, the server MUST
NOT store the new credential.
The PrevLastModified value in the request MUST be the same as the
LastModified value in the stored version of the credential. If not,
then the server MUST respond with an error and MUST NOT store the
new credential.
If the PrevLastModified value is omitted, then the request MUST
relate to a credential not previously stored, i.e. in this case, the
new credential MUST have a new, unique-for-this-account, selector
string value.
4. BEEP Profile for SACRED
The protocol described in this memo is realized as a [BEEP] profile.
Future memos may define alternative versions of the BEEP profile for
SACRED. When a BEEP peer sends its greeting, it indicates which
profiles it is willing to support. Accordingly, when the BEEP client
asks to start a channel, it indicates the versions it supports, and
if any of these are acceptable to the BEEP server, the latter
specifies which profile it is starting.
Profile Identification: http://iana.org/beep/transient/sacred/bss
This profile URI is consistent with [TRANS].
Messages Exchanged during Channel Creation:
InfoRequest,
CreateAccountRequest,
RemoveAccountRequest,
PWChangeRequest,
DownloadRequest,
UploadRequest,
InfoResponse,
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DownloadResponse,
error,
ok
Messages starting one-to-one exchanges:
InfoRequest,
CreateAccountRequest,
RemoveAccountRequest,
PWChangeRequest,
DownloadRequest,
UploadRequest
Messages in positive replies:
ok,
InfoResponse,
DownloadResponse
Messages in negative replies: error
Messages in one-to-many changes: none
Message Syntax: c.f.,Section 3
Message Semantics: c.f., Section 2
Contact Information: c.f., the AuthorsÆ Addresses section of this
memo
4.1 Profile Initialization
There are two ways to perform privacy tuning on a BEEP session,
either:
- a transport security profile may be successfully started; or,
- a user authentication profile that supports transport security may
be successfully started.
Regardless, upon completion of the negotiation process, a tuning
reset occurs in which both BEEP peers issue a new greeting. Consult
Section 3 of [2] for an example of how a BEEP peer may choose to
issue different greetings based on whether privacy is in use.
Any of the messages listed in section 4.2 below may be exchanged
during channel initialization (c.f., Section 2.3.1.2 of [BEEP]),
e.g.,
C: <start number='1'>
C: <profile uri='http://iana.org/beep/transient/sacred/bss'>
C: <![CDATA[<DownloadRequest ...>]]>
C: </profile>
C: </start>
S: <profile uri='http://iana.org/beep/transient/sacred/bss'>
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S: <![CDATA[<DownloadResponse ...>]]>
S: </profile>
Note that BEEP imposes both encoding and length limitations on the
messages that are piggybacked during channel initialization.
4.2 Profile Exchange
All messages are exchanged as "application/beep+xml" (c.f., Section
6.4 of [BEEP]):
Role MSG RPY ERR
---- --- --- ---
I InfoRequest InfoResponse error
I CreateAccountRequest ok error
I RemoveAccountRequest ok error
I PWChangeRequest ok error
I DownloadRequest DownloadResponse error
I UploadRequest ok error
4.3 Error handling
The "error" message from Section 2.3.1.5 of [BEEP] is used to convey
error information. Typically, after flagging an error, a peer will
initiate a graceful release of the BEEP session.
The following BEEP error reply codes from [BEEP] are to be used:
code meaning
==== =======
421 service not available
450 requested action not taken (e.g., lock already in
use)
451 requested action aborted (e.g., local error in
processing)
454 temporary authentication failure
500 general syntax error (e.g., poorly-formed XML)
501 syntax error in parameters (e.g., non-valid XML)
504 parameter not implemented
530 authentication required
534 authentication mechanism insufficient (e.g., too
weak, sequence exhausted, etc.)
535 authentication failure
537 action not authorized for user
538 authentication mechanism requires encryption
550 requested action not taken (e.g., no requested
profiles are acceptable)
553 parameter invalid
554 transaction failed (e.g., policy violation)
The following SACRED-specific error reply codes can also be used:
code meaning
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==== =======
555 Extension (ProcessInfo) used not supported
556 Required extension (ProcessInfo) not present
5. IANA Considerations
If the IANA approves this memo for standards-track publication, then
the IANA registers the BEEP profile specified in Section 4, and
selects an appropriate standards-track URI, e.g.,
http://iana.org/beep/sacred/bss
<<New questions: [default answer, to be used if there's no list
discussion.]
1. should we apply for a port number? [yes]
2. should we define a url scheme? [no] >>
6. Security Considerations
[REQS] calls for specifications to state how they address the
vulnerabilities listed below.
V1. A passive attacker can watch all packets on the network and
later carry out a dictionary attack.
- The use of SRP, cTLS or sTLS counters this vulnerability.
V2. An attacker can attempt to masquerade as a credential server
in an attempt to get a client to reveal information on line
that allows for a later dictionary attack.
- The use of SRP, cTLS or sTLS counters this vulnerability.
V3. An attacker can attempt to get a client to decrypt a chosen
"ciphertext" and get the client to make use of the resulting
plaintext - the attacker may then be able to carry out a
dictionary attack (e.g. if the plaintext resulting from
"decryption" of a random string is used as a DSA private
key).
- The use of SRP, cTLS or sTLS counters this vulnerability.
V4. An attacker could overwrite a repository entry so that when
a user subsequently uses what they think is a good
credential, they expose information about their password
(and hence the "real" credential).
- Server implementations SHOULD take measures to protect the
database. Client MAY use the ClientInfo field to store e.g.
a signature over the Credential, which they then verify
before using the private component.
V5. An attacker can copy a credential server's repository and
carry out a dictionary attack.
- Server implementations SHOULD take measures to protect the
database.
V6. An attacker can attempt to masquerade as a client in an
attempt to get a server to reveal information that allows
for a later dictionary attack.
- The use of the SRP strong password algorithm counters this
to a great extent. Additionally, credential servers MAY
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choose to provide mechanisms that protect against online
dictionary attacks against user account passwords, either by
repeated access attempts to a single user account (varying
the password) or by attempting to access many user accounts
using the same password.
V7. An attacker can persuade a server that a successful login
has occurred, even if it hasn't.
- Client authentication prevents this.
V8. (Upload) An attacker can overwrite someone else's
credentials on the server.
- Only if they know the account password already (thanks to
SRP and cTLS).
V9. (When using password-based authentication) An attacker can
force a password change to a known (or "weak") password.
- Client authentication counters this.
V10. An attacker can attempt a man-in-the-middle attack for lots
of reasons...
- Mutual authentication plus the encryption of subsequent
messages prevents this.
V11. User enters password instead of name.
- The SASL-SRP scheme allows clients and server to use a
hash of the user id, which would make it very hard for an
attacker to detect this happening. However, using this
technique damages interoperability since all clients dealing
with the credential in question MUST know in advance that
the extra hashing step is to be used. If a client uses this
technique, then it SHOULD use the SHA-1 algorithm and base64
encode the output. Servers MUST be able to handle usernames
which are formed in this manner (essentially servers MUST be
able to support random-looking 28 byte usernames).
V12. An attacker could attempt various denial-of-service attacks.
- No specific countermeasures against DoS are proposed.
If the CreateAccountRequest message were sent over a cleartext
channel (or otherwise exposed) then an attacker could mount a
dictionary attack and recover the account password. This is why the
server authenticated TLS transport is REQUIRED for this operation.
If someone steals the server database they can launch a dictionary
attack. If the dictionary attack is successful, the attacker can
decrypt the user's credentials. An attacker that has learned the
user's account password can also upload new credentials, assuming
the user is authorized to modify the credentials, because someone
who knows the user's account password is assumed to be the user.
However, if someone steals the server database and is unsuccessful
at obtaining the user's account password through a dictionary
attack, they will be unable to upload new credentials.
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References
Normative:
[BEEP] Rose, M., "The Blocks Extensible Exchange Protocol
Core", RFC 3080.
[PKCS15] "PKCS #15 v1.1: Cryptographic Token Information Syntax
Standard," RSA Laboratories, June 2000.
[REQS] Arsenault, A., Farrell, S., "Securely Available
Credentials - Requirements", RFC 3157.
[RFC2026] Bradner, S., "The Internet Standards Process -- Revision
3", RFC 2026.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119.
[SASL] Myers, J., "Simple Authentication and Security Layer
(SASL)", RFC 2222.
[SASL-SRP] Burdis, K.R. & Naffah, R., "Secure Remote Password SASL
Mechanism", draft-burdis-cat-srp-sasl-06, January 2002,
work-in-progress
[SRP] Wu, T., "The SRP Authentication and Key Exchange
System", RFC 2945.
[TLS] Dierks, T., "The TLS Protocol - Version 1.0", RFC 2246.
[XMLDSIG] Eastlake, D., et al. "XML-Signature Syntax and
Processing", RFC 2075.
Informative:
[TRANS] Rose, M., "A Transient Prefix for Identifying Profiles
under Development by the Working Groups of the IETF",
draft-mrose-beep-transientid-01, Sedpteber 2001, work-
in-progress
[XKMS] Hallam-Baker, P. (ed), "XML Key Management
Specification", http://www.w3.org/2001/XKMS/, work-in-
progress
[XBULK] Hughes, M (ed), "XML Key Management Specification - Bulk
Operation", http://www.w3.org/2001/XKMS/, work-in-
progress
Acknowledgements
Radia Perlman (radia.perlman@sun.com) and Charlie Kaufman
(ckaufman@iris.com) co-authored earlier versions of this document.
Michael Zolotarev (mzolotar@tpg.com.au) did much of the initial work
adapting an earlier draft to the use of SRP. Marshall Rose
(mrose@dbc.mtview.ca.us) helped out, in particular, with the BEEP
profile. The following people were actively involved in the mailing
list discussions leading to this draft:
David Chizmadia (vze2729k@verizon.net),
Dave Crocker (dcrocker@brandenburg.com),
Lawrence Greenfield (leg+@andrew.cmu.edu),
Dale Gustafson (dale.gustafson@bpsi.net),
Mike Just (Mike.Just@entrust.com),
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John Linn (jlinn@rsasecurity.com),
Neal McBurnett (neal@bcn.boulder.co.us),
Keith Moore (moore@cs.utk.edu),
Bob Morgan (rlmorgan@washington.edu),
Eamon O'Tuathail (eamon.otuathail@clipcode.com),
Magnus Nystrom (magnus@rsasecurity.com),
Gareth Richards (grichards@rsasecurity.com)
Of course, any and all errors remain the editor's responsibility.
Editor's Address
Stephen Farrell,
Baltimore Technologies,
39 Parkgate Street,
Dublin 8,
IRELAND
Phone: +353-1-881-6000
Email: stephen.farrell@baltimore.ie
Full Copyright Statement
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are included on all such copies and derivative works. In addition,
the ASN.1 module presented in Appendix B may be used in whole or in
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Appendix A: XML Schema
<?xml version="1.0"?>
<!--DOCTYPE schema PUBLIC "-//W3C//DTD XMLSchema 200102//EN"
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"XMLSchema.dtd" [
<!ATTLIST schema
xmlns:sacred CDATA #FIXED "sacred-2002-02-01"
>
<!ENTITY sacred 'sacred-2002-02-01''>
<!ENTITY % p ''>
<!ENTITY % s ''>
] -->
<schema targetNamespace="sacred-2002-02-01"
xmlns="http://www.w3.org/2000/10/XMLSchema" xmlns:sacred="sacred-
2002-02-01" xmlns:ds="http://www.w3.org/2000/09/xmldsig#">
<!-- misc - copied from xbulk to avoid dependency -->
<complexType name="ProcessInfoType">
<sequence maxOccurs="unbounded">
<any namespace="##other"/>
</sequence>
</complexType>
<element name="ProcessInfo" type="sacred:ProcessInfoType"/>
<complexType name="ClientInfoType">
<sequence maxOccurs="unbounded">
<any namespace="##other"/>
</sequence>
</complexType>
<element name="ClientInfo" type="sacred:ClientInfoType"/>
<!-- general account handling -->
<!-- Information request -->
<element name="InfoRequest"/>
<element name="InfoResponse">
<complexType>
<sequence>
<element name="Status" type="string" minOccurs="0"/>
<element name="ServerId" type="string"/>
<element name="N" type="ds:CryptoBinary"/>
<element name="g" type="ds:CryptoBinary"/>
<element name="HashAlg" type="uriReference"/>
<element ref="sacred:ProcessInfo" minOccurs="0"/>
<!-- SRP stuff -->
</sequence>
</complexType>
</element>
<!-- Create Account Request -->
<element name="CreateAccountRequest">
<complexType>
<sequence>
<element name="UserId" type="string"/>
<element name="salt" type="sacred:base64Binary"/>
<element name="PasswordVerifier" type="ds:CryptoBinary"/>
<element ref="sacred:ProcessInfo" minOccurs="0"/>
</sequence>
</complexType>
</element>
<!-- reomve account request -->
<element name="RemoveAccountRequest">
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<complexType>
<sequence>
<element ref="sacred:ProcessInfo" minOccurs="0"/>
</sequence>
</complexType>
</element>
<!-- password change request -->
<element name="PWChangeRequest">
<complexType>
<sequence>
<element name="salt" type="sacred:base64Binary"/>
<element name="PasswordVerifier" type="ds:CryptoBinary"/>
<element ref="sacred:ProcessInfo" minOccurs="0"/>
</sequence>
</complexType>
</element>
<!-- credential specific operations -->
<!-- DownLoad Request -->
<element name="DownloadRequest">
<complexType>
<sequence>
<element name="CredSel" type="string" minOccurs="0"/>
<element ref="sacred:ProcessInfo" minOccurs="0"/>
</sequence>
</complexType>
</element>
<!-- Download Response -->
<element name="DownloadResponse">
<complexType>
<sequence>
<element name="Status" type="string" minOccurs="0"/>
<element name="Credential" type="sacred:CredentialType"/>
</sequence>
</complexType>
</element>
<!-- Upload request -->
<element name="UploadRequest">
<complexType>
<sequence>
<element name="PrevLastModified" type="string"
minOccurs="0"/>
<element name="NewCredential" type="sacred:CredentialType"/>
</sequence>
</complexType>
</element>
<!-- A new ds:KeyInfo thing -->
<element name="SacredPKCS15" type="ds:CryptoBinary"/>
<!-- credential -->
<complexType name="CredentialType">
<sequence>
<element name="CredentialSelector" type="string"
minOccurs="0"/>
<element name="LastModified" type="timeInstant"/>
Editor: Farrell [Page 16]
INTERNET-DRAFT January 2002
<element name="TimeToLive" type="string" minOccurs="0"/>
<element ref="sacred:ProcessInfo" minOccurs="0"/>
<element ref="sacred:ClientInfo" minOccurs="0"/>
<element name="Payload" type="ds:KeyInfoType"
minOccurs="0" maxOccurs="unbounded"/>
</sequence>
</complexType>
<!-- if base64Binary isn't in your schema editor then add this -->
<simpleType name="base64Binary">
<restriction base="string"/>
</simpleType>
</schema>
Appendix B: DTD
<<This is semi-automatically generated from the schema above and is
probably therefore inaccurate.>>
<?xml version="1.0" encoding="UTF-8"?>
<!ENTITY % THING "Stuff" >
<!ELEMENT ClientInfo (%THING;)+>
<!ELEMENT ProcessInfo (%THING;)+>
<!ELEMENT SacredPKCS15 (#PCDATA)>
<!ELEMENT Credential (CredentialSelector?, LastModified,
TimeToLive?, ProcessInfo?, ClientInfo?, Payload*)>
<!ELEMENT CredentialSelector (#PCDATA)>
<!ELEMENT LastModified (#PCDATA)>
<!ELEMENT TimeToLive (#PCDATA)>
<!ELEMENT Payload (%THING;)+>
<!ATTLIST Payload
Id ID #IMPLIED
>
<!ELEMENT CreateAccountRequest (UserId, salt, PasswordVerifier,
ProcessInfo?)>
<!ELEMENT UserId (#PCDATA)>
<!ELEMENT salt (#PCDATA)>
<!ELEMENT PasswordVerifier (#PCDATA)>
<!ELEMENT DownloadRequest (CredSel?, ProcessInfo?)>
<!ELEMENT CredSel (#PCDATA)>
<!ELEMENT DownloadResponse (Status?, Credential)>
<!ELEMENT Status (#PCDATA)>
<!ELEMENT InfoRequest (#PCDATA)>
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<!ELEMENT InfoResponse (Status?, ServerId, N, g, HashAlg,
ProcessInfo?)>
<!ELEMENT ServerId (#PCDATA)>
<!ELEMENT N (#PCDATA)>
<!ELEMENT g (#PCDATA)>
<!ELEMENT HashAlg (#PCDATA)>
<!ELEMENT PWChangeRequest (salt, PasswordVerifier, ProcessInfo?)>
<!ELEMENT RemoveAccountRequest (ProcessInfo?)>
<!ELEMENT UploadRequest (PrevLastModified?, NewCredential)>
<!ELEMENT PrevLastModified (#PCDATA)>
<!ELEMENT NewCredential (CredentialSelector?, LastModified,
TimeToLive?, ProcessInfo?, ClientInfo?, Payload*)>
Appendix C: An Example of Tuning with BEEP
Here is what tuning BEEP for authentication and privacy looks like
using SASL and SRP:
L: <wait for incoming connection>
I: <open connection>
L: RPY 0 0 . 0 170
L: Content-Type: application/beep+xml
L:
L: <greeting>
L: <profile uri='http://iana.org/beep/TLS' />
L: <profile uri='http://iana.org/beep/SASL/SRP-SHA-160' />
L: </greeting>
L: END
I: RPY 0 0 . 0 52
I: Content-Type: application/beep+xml
I:
I: <greeting />
I: END
I: MSG 0 1 . 52 184
I: Content-Type: application/beep+xml
I:
I: <start number='1'>
I: <profile uri='http://iana.org/beep/SASL/SRP-SHA-160'>
I: <![CDATA[<blob>...</blob>]]>
I: </profile>
I: </start>
I: END
L: RPY 0 1 . 170 783
L: Content-Type: application/beep+xml
L:
L: <profile uri='http://iana.org/beep/SASL/SRP-SHA-160'>
L: <![CDATA[<blob>...</blob>]]>
L: </profile>
L: END
I: MSG 1 0 . 0 559
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INTERNET-DRAFT January 2002
I: Content-Type: application/beep+xml
I:
I: <blob>...</blob>
I: END
L: RPY 1 0 . 0 429
L: Content-Type: application/beep+xml
L:
L: <blob>...</blob>
L: END
I: MSG 1 1 . 559 82
I: Content-Type: application/beep+xml
I:
I: <blob>...</blob>
I: END
L: RPY 1 2 . 429 66
L: Content-Type: application/beep+xml
L:
L: <blob status='complete' />
L: END
... successful transport security negotiation ...
L: RPY 0 0 . 0 127
L: Content-Type: application/beep+xml
L:
L: <greeting>
L: <profile uri='http://iana.org/beep/transient/sacred/bss' />
L: </greeting>
L: END
I: RPY 0 0 . 0 52
I: Content-Type: application/beep+xml
I:
I: <greeting />
I: END
Appendix D: Provision SACRED using other Protocols
<<This appendix represents the "no other substrates" position. If
the WG concensus were to converge onto also supporting http (say),
then this appendix will change, possibly even moving into the body
of the document.>>
SACRED may be implemented in a non-BEEP environment, providing that
before any SACRED PDUs are sent, the application protocol must be
protected according to the security mandates provided in Section
2.3.
For example, if SACRED is provisioned as the payload of an
application protocol that supports SASL and TLS, then the
appropriate SASL and/or TLS negotiation must successfully occur
before exchanging Sacred PDUs.
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Alternatively, if the application protocol doesn't support SASL,
then one or more PDUs are defined to facilitate a SASL negotiation,
and the appropriate negotiation must occur before exchanging Sacred
PDUs.
Appendix E: Changes & Open Issues
<<Note to RFC editor. Please remove this appendix and its TOC entry
prior to RFC publication.>>
-01: Changes as per mailing list discussion:
- Change from authors to editor + acks
- Included resolved comments from list:
- password -> account pwd or cred pwd as appropriate
- account mgt separated and optional
- added example beep tuning
- selector: no default, omit in d/l means all
- changed LastModified scheme as per list comments
- Excluded administrative operations (was an open issue)
- Demoted hashed(username) concept to a note under security
considerations (see V11).
- Dropped idea of specifying a mapping between SRP id and cTLS
certificate.
- Dropped xkms & xbulk as normative references, but copied some
stuff from them.
-00: This version is adapted from draft-ietf-SACRED-protocol-beep-
pdm-00.txt, the main changes are:
- PDM -> SRP &/or TLS
- Payload security -> SASL or TLS
- Dropped username hashing
- Dropped away-from-home
Major Open Issues:
- Multiple substrates issue
- SASL authorization identity issue
- Simplicity: is there a way to use XML, provide schema and DTD (for
information) but not inherit any generic XML complexity?
Other Open Issues:
- If a server only supports up/down-load, then is SRP alone
sufficient or MUST the server also support cTLS? (The latter
according to the current text.)
- Meaning of empty string for credential selector?
- Does section 2.4 need changes?
- Should we apply for a port number? (probably)
- Should we define a URI scheme? (probably not)
- Should the DTD or schema be normative? I'd usually go for the
schema, but in this case the DTD seems much simpler.
Editor: Farrell [Page 20]
