draft-ietf-xcon-bfcp-connection-01.txt   draft-ietf-xcon-bfcp-connection-02.txt 
XCON Working Group G. Camarillo XCON Working Group G. Camarillo
Internet-Draft Ericsson Internet-Draft Ericsson
Expires: December 25, 2006 June 23, 2006 Expires: March 19, 2007 September 15, 2006
Connection Establishment in the Binary Floor Control Protocol (BFCP) Connection Establishment in the Binary Floor Control Protocol (BFCP)
draft-ietf-xcon-bfcp-connection-01.txt draft-ietf-xcon-bfcp-connection-02.txt
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Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2006). Copyright (C) The Internet Society (2006).
Abstract Abstract
This document specifies how a Binary Floor Control Protocol (BFCP) This document specifies how a Binary Floor Control Protocol (BFCP)
client establishes a connection to a BFCP floor control server client establishes a connection to a BFCP floor control server
outside the context of an offer/answer exchange. This document also outside the context of an offer/answer exchange. This document also
specifies a digest authentication mechanism for BFCP based on shared specifies a digest authentication mechanism for BFCP based on shared
secrets. secrets.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. TCP Connection Establishment . . . . . . . . . . . . . . . . . 3 3. TCP Connection Establishment . . . . . . . . . . . . . . . . . 3
4. TLS Usage . . . . . . . . . . . . . . . . . . . . . . . . . . 4 4. TLS Usage . . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Authentication . . . . . . . . . . . . . . . . . . . . . . . . 4 5. Authentication . . . . . . . . . . . . . . . . . . . . . . . . 5
5.1. Certificate-based Mutual Authentication . . . . . . . . . 4 5.1. Certificate-based Mutual Authentication . . . . . . . . . 5
5.2. Digest-based Client Authentication . . . . . . . . . . . . 5 5.2. Digest-based Client Authentication . . . . . . . . . . . . 5
5.2.1. Client Behavior . . . . . . . . . . . . . . . . . . . 5 5.2.1. Client Behavior . . . . . . . . . . . . . . . . . . . 6
5.2.2. Floor Control Server Behavior . . . . . . . . . . . . 6 5.2.2. Floor Control Server Behavior . . . . . . . . . . . . 7
5.3. Attribute Definitions . . . . . . . . . . . . . . . . . . 7 5.3. Attribute Definitions . . . . . . . . . . . . . . . . . . 8
5.3.1. NONCE . . . . . . . . . . . . . . . . . . . . . . . . 7 5.3.1. NONCE . . . . . . . . . . . . . . . . . . . . . . . . 8
5.3.2. DIGEST . . . . . . . . . . . . . . . . . . . . . . . . 8 5.3.2. DIGEST . . . . . . . . . . . . . . . . . . . . . . . . 8
5.4. Error Code Definitions . . . . . . . . . . . . . . . . . . 9 5.4. Error Code Definitions . . . . . . . . . . . . . . . . . . 10
5.5. Security Considerations . . . . . . . . . . . . . . . . . 9 5.5. Security Considerations . . . . . . . . . . . . . . . . . 10
5.6. IANA Considerations . . . . . . . . . . . . . . . . . . . 11 5.6. IANA Considerations . . . . . . . . . . . . . . . . . . . 12
5.6.1. Attribute Registration . . . . . . . . . . . . . . . . 11 5.6.1. Attribute Registration . . . . . . . . . . . . . . . . 12
5.6.2. Error Code Registration . . . . . . . . . . . . . . . 11 5.6.2. Error Code Registration . . . . . . . . . . . . . . . 12
5.6.3. Digest Algorithm Subregistry . . . . . . . . . . . . . 11 5.6.3. Digest Algorithm Subregistry . . . . . . . . . . . . . 12
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13
7. Normative References . . . . . . . . . . . . . . . . . . . . . 12 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 13 7.1. Normative References . . . . . . . . . . . . . . . . . . . 13
Intellectual Property and Copyright Statements . . . . . . . . . . 14 7.2. Informative References . . . . . . . . . . . . . . . . . . 14
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 15
Intellectual Property and Copyright Statements . . . . . . . . . . 16
1. Introduction 1. Introduction
As discussed in the BFCP (Binary Floor Control Protocol) As discussed in the BFCP (Binary Floor Control Protocol)
specification [6], a given BFCP client needs a set of data in order specification [9], a given BFCP client needs a set of data in order
to establish a BFCP connection to a floor control server. These data to establish a BFCP connection to a floor control server. These data
include the transport address of the server, the conference include the transport address of the server, the conference
identifier, and the user identifier. identifier, and the user identifier.
Once a client obtains this information, it needs to establish a BFCP Once a client obtains this information, it needs to establish a BFCP
connection to the floor control server. The way this connection is connection to the floor control server. The way this connection is
established depends on the context of the client and the floor established depends on the context of the client and the floor
control server. How to establish such a connection in the context of control server. How to establish such a connection in the context of
an offer/answer [4] exchange between a client and a floor control an SDP [8] offer/answer [4] exchange between a client and a floor
server is specified in [7]. This document specifies how a client control server is specified in [10]. This document specifies how a
establishes a connection to a floor control server outside the client establishes a connection to a floor control server outside the
context of an offer/answer exchange. context of an SDP offer/answer exchange.
BFCP entities establishing a connection outside an offer/answer BFCP entities establishing a connection outside an SDP offer/answer
exchange need different authentication mechanisms than entities using exchange need different authentication mechanisms than entities using
offer/answer exchanges. This is because offer/answer exchanges offer/answer exchanges. This is because offer/answer exchanges
provide parties with an initial integrity-protected channel that provide parties with an initial integrity-protected channel that
clients and floor control servers can use to exchange the clients and floor control servers can use to exchange the
fingerprints of their self-signed certificates. Outside the offer/ fingerprints of their self-signed certificates. Outside the offer/
answer model, such a channel is not typically available. This answer model, such a channel is not typically available. This
document defines a digest mechanism for BFCP that is based on shared document defines a digest mechanism for BFCP that is based on shared
secrets. secrets.
2. Terminology 2. Terminology
In this document, the key words "MUST", "MUST NOT", "REQUIRED", In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT
RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as
described in BCP 14, RFC 2119 [2] and indicate requirement levels for described in BCP 14, RFC 2119 [2] and indicate requirement levels for
compliant implementations. compliant implementations.
3. TCP Connection Establishment 3. TCP Connection Establishment
A given BFCP client needs a set of data in order to establish a BFCP As stated in Section 1, a given BFCP client needs a set of data in
connection to a floor control server. These data include the order to establish a BFCP connection to a floor control server.
transport address of the server, the conference identifier, and the These data include the transport address of the server, the
user identifier. It is outside the scope of this document to specify conference identifier, and the user identifier. It is outside the
how a client obtains this information. This document assumes that scope of this document to specify how a client obtains this
the client obtains this information using an out-of-band method. information. This document assumes that the client obtains this
information using an out-of-band method.
Once the client has the transport address of the floor control Once the client has the transport address (i.e., IP address and port)
server, it initiates a TCP connection towards it. That is, the of the floor control server, it initiates a TCP connection towards
client performs an active TCP open. it. That is, the client performs an active TCP open.
OPEN ISSUE: do we want to define DNS procedures here? If so, do we If the client is provided with the floor control server's host name
want to define SRV procedures or are A and AAAA RRs enough? instead of with its IP address, the client MUST perform a DNS lookup
in order to resolve the host name into an IP address. Clients
eventually perform an A or AAAA DNS lookup (or both) on the host
name.
The BFCP specification [6] describes a number of situations when the In order to translate the host name to the corresponding set of IP
addresses, IPv6-only or dual-stack clients MUST use the newer
getaddrinfo() name lookup function, instead of gethostbyname() [7].
The new function implements the Source and Destination Address
Selection algorithms specified in [12], and is expected to be
supported by all IPv6 hosts.
The advantage of the additional complexity is that this technique
will output an ordered list of IPv6/IPv4 destination addresses based
on the relative merits of the corresponding source/destination pairs.
This will guarantee optimal routing. However, the Source and
Destination Selection algorithms of [6] are dependent on broad
operating system support and uniform implementation of the
application programming interfaces that implement this behavior.
Developers should carefully consider the issues described by Roy
et al. [11] with respect to address resolution delays and address
selection rules. For example, implementations of getaddrinfo()
may return address lists containing IPv6 global addresses at the
top of the list and IPv4 addresses at the bottom, even when the
host is only configured with an IPv6 local scope (e.g., link-
local) and an IPv4 address. This will, of course, introduce a
delay in completing the connection.
The BFCP specification [9] describes a number of situations when the
TCP connection between a client and the floor control server needs to TCP connection between a client and the floor control server needs to
be reestablished. However, that specification does not describe the be reestablished. However, that specification does not describe the
reestablishment process because this process depends on how the reestablishment process because this process depends on how the
connection was established in the first place. connection was established in the first place.
When the existing TCP connection is reseted following the rules in When the existing TCP connection is closed following the rules in
[6], the client SHOULD reestablish the connection towards the floor [9], the client SHOULD reestablish the connection towards the floor
control server. If a TCP connection cannot deliver a BFCP message control server. If a TCP connection cannot deliver a BFCP message
from the client to the floor control server and times out, the client from the client to the floor control server and times out, the client
SHOULD reestablish the TCP connection. SHOULD reestablish the TCP connection.
OPEN ISSUE: do we want to have floor control servers reestablish
connections as well?
4. TLS Usage 4. TLS Usage
All BFCP entities implement TLS and SHOULD use it in all their All BFCP entities implement TLS and SHOULD use it in all their
connections. TLS provides integrity and replay protection, and connections. TLS provides integrity and replay protection, and
optional confidentiality. The floor control server MUST always act optional confidentiality. The floor control server MUST always act
as the TLS server. as the TLS server.
A floor control server that receives a BFCP message over TCP (no TLS) A floor control server that receives a BFCP message over TCP (no TLS)
can request the use of TLS by generating an Error message with an can request the use of TLS by generating an Error message with an
Error code with a value of 9 (Use TLS) Error code with a value of 9 (Use TLS).
5. Authentication 5. Authentication
BFCP supports certificate-based mutual authentication between clients BFCP supports certificate-based mutual authentication between clients
and floor control servers, as specified in Section 5.1. and floor control servers, as specified in Section 5.1.
Additionally, BFCP also provides a digest mechanism based on a shared Additionally, BFCP also provides a digest mechanism based on a shared
secret to provide client authentication for clients without secret to provide client authentication for clients without
certificates. This digest mechanism is described in Section 5.2. certificates. This digest mechanism is described in Section 5.2.
5.1. Certificate-based Mutual Authentication 5.1. Certificate-based Mutual Authentication
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SHOULD also present their certificates to the floor control server. SHOULD also present their certificates to the floor control server.
The certificates provided at the TLS-level MUST either be directly The certificates provided at the TLS-level MUST either be directly
signed by one of the other party's trust anchors or be validated signed by one of the other party's trust anchors or be validated
using a certification path that terminates at one of the other using a certification path that terminates at one of the other
party's trust anchors [5]. party's trust anchors [5].
5.2. Digest-based Client Authentication 5.2. Digest-based Client Authentication
Clients without certificates can authenticate themselves to the floor Clients without certificates can authenticate themselves to the floor
control servers using a digest-based mechanism instead. BFCP control server using a digest-based mechanism instead. BFCP supports
supports digest-based client authentication based on a shared secret digest-based client authentication based on a shared secret between a
between a client and the floor control server. The floor control client and the floor control server. The floor control server of a
server of a conference shares a secret with each of the participants conference shares a secret with each of the participants in the
in the conference and can request them to sign their messages using conference and can request them to sign their messages using that
that shared secret. Consequently, there is a need for a mechanism to shared secret. Consequently, there is a need for a mechanism to
generate such a shared secret. However, such mechanism is outside generate such a shared secret. However, such mechanism is outside
the scope of this document. This document assumes that shared the scope of this document. This document assumes that shared
secrets are generated and exchanged using out-of-band means. secrets are generated and exchanged using out-of-band means.
However, shared secrets MUST be at least as long as the length of the
output of the digest algorithm used, as recommended in [1].
Digest-based client authentication in BFCP is based on the DIGEST Digest-based client authentication in BFCP is based on the DIGEST
attribute, which is defined in Section 5.3.2. This attribute, which attribute, which is defined in Section 5.3.2. This attribute, which
always appears as the last attribute in a message, contains an always appears as the last attribute in a message, contains an
algorithm identifier and a keyed digest of the BFCP message using algorithm identifier and a keyed digest of the BFCP message using
that algorithm. The text used as input to the digest algorithm is that algorithm. The text used as input to the digest algorithm is
the BFCP message, including the common header, up to and including the BFCP message, including the common header, up to and including
the attribute preceding the DIGEST attribute. Depending on the the attribute preceding the DIGEST attribute. Depending on the
algorithm, this text may need to be padded with zeroes. algorithm, this text may need to be padded with zeroes.
Section 5.3.2 lists the algorithms specified in BFCP. Section 5.3.2 lists the algorithms specified in BFCP.
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(to avoid replay attacks). Clients prove the freshness of a message (to avoid replay attacks). Clients prove the freshness of a message
by including a NONCE attribute in the message. by including a NONCE attribute in the message.
Clients can obtain the digest algorithms supported by the floor Clients can obtain the digest algorithms supported by the floor
control server in an Error response from the floor control server control server in an Error response from the floor control server
with Error Code 10 (DIGEST Attribute Required). A client SHOULD use with Error Code 10 (DIGEST Attribute Required). A client SHOULD use
the first digest algorithm in the list that it supports. the first digest algorithm in the list that it supports.
The nonce to be placed in the NONCE attribute by the client is The nonce to be placed in the NONCE attribute by the client is
typically provided by the floor control server in an Error response typically provided by the floor control server in an Error response
-- typically with Error Code 10 (DIGEST Attribute Required) or 6 with Error Code 10 (DIGEST Attribute Required) or 6 (Invalid Nonce).
(Invalid Nonce). If a client generates a message without a DIGEST If a client generates a message without a DIGEST attribute and
attribute and receives an Error response with Error Code 10 (DIGEST receives an Error response with Error Code 10 (DIGEST Attribute
Attribute Required), the client SHOULD re-send the message with a Required), the client SHOULD resend the message with a DIGEST
DIGEST attribute and a NONCE attribute with the nonce received in the attribute and a NONCE attribute with the nonce received in the Error
Error response. response.
If after sending a message with a DIGEST attribute, a client receives If after sending a message with a DIGEST attribute, a client receives
an Error response with Error Code 11 (Invalid Nonce), the client an Error response with Error Code 11 (Invalid Nonce), the client
SHOULD re-send the message using the new nonce received in the Error SHOULD resend the message using the new nonce received in the Error
response. If the Error Code is 12 (Authentication Failed) instead, response. If the Error Code is 12 (Authentication Failed) instead,
the client MUST NOT send further messages to the floor control server the client MUST NOT send further messages to the floor control server
until it has obtained a different (hopefully valid) shared secret until it has obtained a different (hopefully valid) shared secret
than the one used in the original message. than the one used in the original message.
If a client receives a nonce in a message from the floor control If a client receives a nonce in a message from the floor control
server, the client SHOULD add a NONCE attribute with this nonce and a server, the client SHOULD add a NONCE attribute with this nonce and a
DIGEST attribute to its next message to the floor control server. DIGEST attribute to its next message to the floor control server.
5.2.2. Floor Control Server Behavior 5.2.2. Floor Control Server Behavior
If the floor control server receives a message without DIGEST If the floor control server receives a message without DIGEST
attribute from an unauthenticated client, the floor control server attribute from an unauthenticated client, the floor control server
responds with an Error message with Error Code 10 (DIGEST Attribute responds with an Error message with Error Code 10 (DIGEST Attribute
Required). The floor control message MUST include a list with the Required). The floor control message MUST include a list with the
digest algorithms supported by the floor control server in order of digest algorithms supported by the floor control server in order of
preference (i.e., the first algorithm is the most preferred) and a preference (i.e., the first algorithm is the most preferred) and a
NONCE attribute with a nonce value that is unguessable by attackers. NONCE attribute with a nonce value. Floor control servers MUST NOT
use the same nonce for the same shared secret more than once.
When a floor control server receives a BFCP message with a DIGEST When a floor control server receives a BFCP message with a DIGEST
attribute, it checks whether the Algorithm identifier in the DIGEST attribute, it checks whether the Algorithm identifier in the DIGEST
attribute corresponds to an algorithm that is supported by the floor attribute corresponds to an algorithm that is supported by the floor
control server. If it does not, the floor control server SHOULD control server. If it does not, the floor control server SHOULD
return an Error message with Error Code 10 (DIGEST Attribute return an Error message with Error Code 10 (DIGEST Attribute
Required) with a list with the digest algorithms supported by the Required) with a list with the digest algorithms supported by the
floor control server. floor control server.
If the algorithm identifier is valid, the floor control server checks If the algorithm identifier is valid, the floor control server checks
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successful. successful.
If the resulting value is different than the one in the DIGEST If the resulting value is different than the one in the DIGEST
attribute, authentication is considered to have failed, in which case attribute, authentication is considered to have failed, in which case
the server SHOULD return an Error message with Error Code 12 the server SHOULD return an Error message with Error Code 12
(Authentication Failed). Messages from a client that cannot be (Authentication Failed). Messages from a client that cannot be
authenticated MUST NOT be processed further. authenticated MUST NOT be processed further.
Floor control servers MAY include a NONCE attribute in their Floor control servers MAY include a NONCE attribute in their
responses to provide the nonce to be used in the next message by the responses to provide the nonce to be used in the next message by the
client. However, when TLS is used, floor control servers typically client. However, when TLS is used, floor control servers MAY choose
authenticate only the first message sent over the TLS connection. to only authenticate the first message sent over the TLS connection.
This way, the client does not need to sign every message it sends
OPEN ISSUE: do we want to state that servers typically authenticate (message signatures can be long when compared with BFCP messages).
only the first message sent over the TLS connection? Reducing the size of BFCP messages can considerably reduce
transmission times over low-bandwidth links.
5.3. Attribute Definitions 5.3. Attribute Definitions
The following new attribute types are defined: The following new attribute types are defined:
+------+-----------+-------------+ +------+-----------+-------------+
| Type | Attribute | Format | | Type | Attribute | Format |
+------+-----------+-------------+ +------+-----------+-------------+
| 17 | NONCE | Unsigned16 | | 19 | NONCE | Unsigned16 |
| 18 | DIGEST | OctetString | | 20 | DIGEST | OctetString |
+------+-----------+-------------+ +------+-----------+-------------+
Table 1: BFCP attributes Table 1: BFCP attributes
Both are EXTENSION-ATTRIBUTES are specified in [6]. Both are EXTENSION-ATTRIBUTES as specified in [9].
5.3.1. NONCE 5.3.1. NONCE
The NONCE attribute can appear in any message. The following is the The NONCE attribute can appear in any message. The NONCE attribute
format of the NONCE attribute. MUST be the last attribute of messages that do not contain a DIGEST
attribute and the second to last attribute of messages that contain a
DIGEST attribute (the DIGEST attribute is always the last). The
following is the format of the NONCE attribute.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 1 0 0 0 1|M|0 0 0 0 0 1 0 0| Nonce Value | |0 0 1 0 0 1 1|M|0 0 0 0 0 1 0 0| Nonce Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: NONCE format Figure 1: NONCE format
Nonce Value: this 16-bit field contains a nonce. Nonce Value: this 16-bit field contains a nonce.
5.3.2. DIGEST 5.3.2. DIGEST
The DIGEST attribute can only appear in messages sent by clients. The DIGEST attribute can only appear in messages sent by clients.
The DIGEST attribute MUST be the last attribute of the message in The DIGEST attribute MUST be the last attribute of the message in
which it appears. The following is the format of the DIGEST which it appears. The following is the format of the DIGEST
attribute. attribute.
0 1 2 3 0 1 2 3
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5.3.2. DIGEST 5.3.2. DIGEST
The DIGEST attribute can only appear in messages sent by clients. The DIGEST attribute can only appear in messages sent by clients.
The DIGEST attribute MUST be the last attribute of the message in The DIGEST attribute MUST be the last attribute of the message in
which it appears. The following is the format of the DIGEST which it appears. The following is the format of the DIGEST
attribute. attribute.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 1 0 0 1 0|M|0 0 0 1 1 0 0 0| Algorithm | | |0 0 1 0 1 0 0|M| Length | Algorithm | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | | |
| | | |
| | | |
/ Digest / / Digest /
/ / / /
| | | |
| | | |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Padding | | | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: DIGEST format Figure 2: DIGEST format
Algorithm: this 8-bit field contains the identifier of the algorithm Algorithm: this 8-bit field contains the identifier of the algorithm
used to calculate the keyed digest. The following are the algorithm used to calculate the keyed digest. The following are the
identifiers defined: algorithm identifiers defined:
+------------+-----------+---------------+--------------+ +------------+-----------+---------------+--------------+
| Identifier | Algorithm | Digest Length | Reference | | Identifier | Algorithm | Digest Length | Reference |
+------------+-----------+---------------+--------------+ +------------+-----------+---------------+--------------+
| 0 | HMAC-SHA1 | 20 bytes | RFC 2104 [1] | | 0 | HMAC-SHA1 | 20 bytes | RFC 2104 [1] |
+------------+-----------+---------------+--------------+ +------------+-----------+---------------+--------------+
Table 2: Digest algorithms Table 2: Digest algorithms
The text used as input to the digest algorithm is the BFCP The text used as input to the digest algorithm is the BFCP
message, including the common header, up to and including the message, including the common header, up to and including the
attribute preceding the DIGEST attribute. Depending on the attribute preceding the DIGEST attribute. Depending on the
algorithm, this text may need to be padded with zeroes. When algorithm, this text may need to be padded with zeroes.
HMAC-SHA1 is used, the input text needs to be padded so as to be a
multiple of 64 bytes.
The key used as input to the keyed digest is the secret shared The key used as input to the keyed digest is the secret shared
between the server and the user identified by the User ID in the between the server and the user identified by the User ID in the
common header of the message. common header of the message.
Digest: this field contains a keyed digest of the BFCP message. Its Digest: this field contains a keyed digest of the BFCP message. Its
calculation is described in Section 5.2. calculation is described in Section 5.2.
Padding: padding added so that the contents of the DIGEST attribute Padding: padding added so that the contents of the DIGEST attribute
is 32-bit aligned. The Padding bits SHOULD be set to zero by the is 32-bit aligned. The Padding bits SHOULD be set to zero by the
sender and MUST be ignored by the receiver. sender and MUST be ignored by the receiver.
5.4. Error Code Definitions 5.4. Error Code Definitions
This specification defines the following new BFCP Error Codes:
+-------+---------------------------+ +-------+---------------------------+
| Value | Meaning | | Value | Meaning |
+-------+---------------------------+ +-------+---------------------------+
| 10 | DIGEST Attribute Required | | 10 | DIGEST Attribute Required |
| 11 | Invalid Nonce | | 11 | Invalid Nonce |
| 12 | Authentication Failed | | 12 | Authentication Failed |
+-------+---------------------------+ +-------+---------------------------+
Table 3: Error Code meaning Table 3: Error Code meaning
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| | | |
/ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Algorithm ID | Algorithm ID | | | Algorithm ID | Algorithm ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Algorithm ID | Algorithm ID | | Algorithm ID | Algorithm ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Digest algorithms format Figure 3: Digest algorithms format
Algorithm ID: these 8-bit fields contain the identifiers of the Algorithm ID: these 8-bit fields contain the identifiers of the
digest algorithms supported by the floor control server in order of digest algorithms supported by the floor control server in order
preference (i.e., the first algorithm is the most preferred). of preference (i.e., the first algorithm is the most preferred).
5.5. Security Considerations 5.5. Security Considerations
BFCP can use TLS or message signatures to provide client BFCP can use TLS or message signatures to provide client
authentication. Floor control server authentication is based on TLS, authentication. Floor control server authentication is based on TLS,
which also provides replay and integrity protection, and which also provides replay and integrity protection, and
confidentiality. It is RECOMMENDED that TLS with non-null encryption confidentiality. It is RECOMMENDED that TLS with non-null encryption
is always used and that the first message from an unauthenticated is always used and that the first message from an unauthenticated
client over a given TLS connection is signed using the DIGEST client over a given TLS connection is challenged by the floor control
attribute. Clients and floor control servers MAY use other security server. Clients and floor control servers MAY use other security
mechanisms as long as they provide similar security properties. mechanisms as long as they provide similar security properties (i.e.,
replay and integrity protection, confidentiality, and server
OPEN ISSUE: same as before. Do we want to say that we recommend to authentication).
sign only the first message over a TLS connection?
The remainder of this Section analyzes some of the threats against The remainder of this Section analyzes some of the threats against
BFCP and how they are addressed. BFCP and how they are addressed.
An attacker may attempt to impersonate a client (a floor participant An attacker may attempt to impersonate a client (a floor participant
or a floor chair) in order to generate forged floor requests or to or a floor chair) in order to generate forged floor requests or to
grant or deny existing floor requests. Client impersonation is grant or deny existing floor requests. Client impersonation is
avoided by having clients sign their messages. A nonce is included avoided by having clients sign their messages. A nonce is included
in the signature to ensure the freshness of the message. If the in the signature to ensure the freshness of the message. If the
client is using a TLS connection to communicate with the floor client is using a TLS connection to communicate with the floor
skipping to change at page 10, line 38 skipping to change at page 11, line 28
was initially authenticated. If TLS-based client authentication is was initially authenticated. If TLS-based client authentication is
used, there is not need for the client to sign BFCP messages over the used, there is not need for the client to sign BFCP messages over the
connection. connection.
An attacker may attempt to impersonate a floor control server. A An attacker may attempt to impersonate a floor control server. A
successful attacker would be able to make clients think that they successful attacker would be able to make clients think that they
hold a particular floor so that they would try to access a resource hold a particular floor so that they would try to access a resource
(e.g., sending media) without having legitimate rights to access it. (e.g., sending media) without having legitimate rights to access it.
Floor control server impersonation is avoided by having floor control Floor control server impersonation is avoided by having floor control
servers present their server certificates at TLS connection servers present their server certificates at TLS connection
establishment time. establishment time. Clients MUST NOT send any signed BFCP message to
an unauthenticated floor control server in order to prevent man-in-
the-middle attacks.
Attackers may attempt to modify messages exchanged by a client and a Attackers may attempt to modify messages exchanged by a client and a
floor control server. The integrity protection provided by TLS floor control server. The integrity protection provided by TLS
connections prevents this attack. connections prevents this attack.
An attacker may attempt to fetch a valid message sent by a client to An attacker may attempt to fetch a valid message sent by a client to
a floor control server and replay it at a later point. If the a floor control server and replay it at a later point. If the
message was signed, the attacker may attempt to establish a new TLS message was signed, the attacker may attempt to establish a new TLS
connection with the floor control server and replay the message over connection with the floor control server and replay the message over
the new connection. Using TLS confidentiality prevents this attack the new connection. The use of nonces avoids this type of attack.
because the attacker cannot access the contents of the message in the As stated in Section 5.2.2, floor control servers do not use the same
first place. Additionally, TLS provides replay protection for a nonce for the same shared secret more than once.
given connection. Therefore, it is strongly RECOMMENDED that TLS is
used with a non-null encryption algorithm. Using TLS confidentiality also prevents that attack because the
attacker cannot access the contents of the message in the first
place. Additionally, TLS provides replay protection within a given
connection. Therefore, it is RECOMMENDED that TLS is used with a
non-null encryption algorithm.
Attackers may attempt to pick messages from the network to get access Attackers may attempt to pick messages from the network to get access
to confidential information between the floor control server and a to confidential information between the floor control server and a
client (e.g., why a floor request was denied). TLS confidentiality client (e.g., why a floor request was denied). TLS confidentiality
prevents this attack. prevents this attack.
5.6. IANA Considerations 5.6. IANA Considerations
The following sections instruct the IANA to perform a set of actions. The following sections instruct the IANA to perform a set of actions.
5.6.1. Attribute Registration 5.6.1. Attribute Registration
The IANA is instructed to register the following new values under the The IANA is instructed to register the following new values under the
Attribute subregistry under the BFCP Parameters registry. Attribute subregistry under the BFCP Parameters registry.
+------+-----------+------------+ +------+-----------+------------+
| Type | Attribute | Reference | | Type | Attribute | Reference |
+------+-----------+------------+ +------+-----------+------------+
| 17 | NONCE | [RFC XXXX] | | 19 | NONCE | [RFC XXXX] |
| 18 | DIGEST | [RFC XXXX] | | 20 | DIGEST | [RFC XXXX] |
+------+-----------+------------+ +------+-----------+------------+
Table 4: New values of the BFCP Attribute subregistry Table 4: New values of the BFCP Attribute subregistry
[Note to the RFC editor: please, replace RFCxxxx with the RFC number
that will be assigned to this document.]
5.6.2. Error Code Registration 5.6.2. Error Code Registration
The IANA is instructed to register the following new values under the The IANA is instructed to register the following new values under the
Error Code subregistry under the BFCP Parameters registry. Error Code subregistry under the BFCP Parameters registry.
+-------+---------------------------+------------+ +-------+---------------------------+------------+
| Value | Meaning | Reference | | Value | Meaning | Reference |
+-------+---------------------------+------------+ +-------+---------------------------+------------+
| 10 | DIGEST Attribute Required | [RFC XXXX] | | 10 | DIGEST Attribute Required | [RFC XXXX] |
| 11 | Invalid Nonce | [RFC XXXX] | | 11 | Invalid Nonce | [RFC XXXX] |
| 12 | Authentication Failed | [RFC XXXX] | | 12 | Authentication Failed | [RFC XXXX] |
+-------+---------------------------+------------+ +-------+---------------------------+------------+
Table 5: New Values of the Error Code subregistry Table 5: New Values of the Error Code subregistry
[Note to the RFC editor: please, replace RFCxxxx with the RFC number
that will be assigned to this document.]
5.6.3. Digest Algorithm Subregistry 5.6.3. Digest Algorithm Subregistry
This Section establishes the Digest Algorithm subregistry under the This Section establishes the Digest Algorithm subregistry under the
BFCP Parameters registry. As per the terminology in RFC 2434 [3], BFCP Parameters registry. As per the terminology in RFC 2434 [3],
the registration policy for BFCP digest algorithms shall be the registration policy for BFCP digest algorithms shall be
"Specification Required". For the purposes of this subregistry, the "Specification Required".
BFCP error codes for which IANA registration is requested MUST be
defined by a standards-track RFC. Such RFC MUST specify the value
and the semantics of the error code, and any Error Specific Details
that apply to it.
For each BFCP digest algorithm, the IANA registers its numeric For each BFCP digest algorithm, the IANA registers its numeric
identifier, its name, and the reference to the RFC where the identifier, its name, and the reference to the specification where
algorithm is defined. The following table contains the initial the algorithm is defined. The following table contains the initial
values of this subregistry. values of this subregistry.
+------------+-----------+-----------+ +------------+-----------+-----------+
| Identifier | Algorithm | Reference | | Identifier | Algorithm | Reference |
+------------+-----------+-----------+ +------------+-----------+-----------+
| 0 | HMAC-SHA1 | RFC 2104 | | 0 | HMAC-SHA1 | RFC 2104 |
+------------+-----------+-----------+ +------------+-----------+-----------+
Table 6: Initial values of the Digest Algorithms subregistry Table 6: Initial values of the Digest Algorithms subregistry
6. Acknowledgments 6. Acknowledgments
Sam Hartman provided useful comments on this document. Sam Hartman and Karim El Malki provided useful comments on this
document.
7. Normative References 7. References
7.1. Normative References
[1] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-Hashing [1] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-Hashing
for Message Authentication", RFC 2104, February 1997. for Message Authentication", RFC 2104, February 1997.
[2] Bradner, S., "Key words for use in RFCs to Indicate Requirement [2] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997. Levels", BCP 14, RFC 2119, March 1997.
[3] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA [3] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", BCP 26, RFC 2434, October 1998. Considerations Section in RFCs", BCP 26, RFC 2434,
October 1998.
[4] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with [4] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with
Session Description Protocol (SDP)", RFC 3264, June 2002. Session Description Protocol (SDP)", RFC 3264, June 2002.
[5] Housley, R., Polk, W., Ford, W., and D. Solo, "Internet X.509 [5] Housley, R., Polk, W., Ford, W., and D. Solo, "Internet X.509
Public Key Infrastructure Certificate and Certificate Revocation Public Key Infrastructure Certificate and Certificate
List (CRL) Profile", RFC 3280, April 2002. Revocation List (CRL) Profile", RFC 3280, April 2002.
[6] Camarillo, G., "The Binary Floor Control Protocol (BFCP)", [6] Draves, R., "Default Address Selection for Internet Protocol
version 6 (IPv6)", RFC 3484, February 2003.
[7] Shin, M-K., Hong, Y-G., Hagino, J., Savola, P., and E. Castro,
"Application Aspects of IPv6 Transition", RFC 4038, March 2005.
[8] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, July 2006.
[9] Camarillo, G., "The Binary Floor Control Protocol (BFCP)",
draft-ietf-xcon-bfcp-06 (work in progress), December 2005. draft-ietf-xcon-bfcp-06 (work in progress), December 2005.
[7] Camarillo, G., "Session Description Protocol (SDP) Format for [10] Camarillo, G., "Session Description Protocol (SDP) Format for
Binary Floor Control Protocol (BFCP) Streams", Binary Floor Control Protocol (BFCP) Streams",
draft-ietf-mmusic-sdp-bfcp-03 (work in progress), December 2005. draft-ietf-mmusic-sdp-bfcp-03 (work in progress),
December 2005.
7.2. Informative References
[11] Roy, S., "IPv6 Neighbor Discovery On-Link Assumption Considered
Harmful", draft-ietf-v6ops-onlinkassumption-04 (work in
progress), January 2006.
Author's Address Author's Address
Gonzalo Camarillo Gonzalo Camarillo
Ericsson Ericsson
Hirsalantie 11 Hirsalantie 11
Jorvas 02420 Jorvas 02420
Finland Finland
Email: Gonzalo.Camarillo@ericsson.com Email: Gonzalo.Camarillo@ericsson.com
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