draft-ietf-msec-srtp-tesla-01.txt   draft-ietf-msec-srtp-tesla-02.txt 
Internet Engineering Task Force Baugher (Cisco) Internet Engineering Task Force Baugher (Cisco)
MSEC Working Group Carrara (Ericsson) MSEC Working Group Carrara (Ericsson)
INTERNET-DRAFT INTERNET-DRAFT
EXPIRES: January 2005 July 2004 EXPIRES: April 2005 October 2004
The Use of TESLA in SRTP The Use of TESLA in SRTP
<draft-ietf-msec-srtp-tesla-01.txt> <draft-ietf-msec-srtp-tesla-02.txt>
Status of this memo Status of this memo
By submitting this Internet-Draft, the authors certify that any By submitting this Internet-Draft, the authors certify that any
applicable patent or other IPR claims of which I am (we are) aware applicable patent or other IPR claims of which I am (we are) aware
have been disclosed, and any of which I (we) become aware will be have been disclosed, and any of which I (we) become aware will be
disclosed, in accordance with RFC 3668 (BCP 79). disclosed, in accordance with RFC 3668 (BCP 79).
By submitting this Internet-Draft, the authors accept the provisions By submitting this Internet-Draft, the authors accept the provisions
of Section 3 of RFC 3667 (BCP 78). of Section 3 of RFC 3667 (BCP 78).
Internet-Drafts are working documents of the Internet Engineering
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4. Usage of TESLA within SRTP.....................................4 4. Usage of TESLA within SRTP.....................................4
4.1. The TESLA extension..........................................4 4.1. The TESLA extension..........................................4
4.2. SRTP Packet Format...........................................5 4.2. SRTP Packet Format...........................................5
4.3. Extension of the SRTP Cryptographic Context..................7 4.3. Extension of the SRTP Cryptographic Context..................7
4.4. SRTP Processing..............................................8 4.4. SRTP Processing..............................................8
4.4.1 Sender Processing...........................................8 4.4.1 Sender Processing...........................................8
4.4.2 Receiver Processing.........................................9 4.4.2 Receiver Processing.........................................9
4.5. SRTCP Packet Format.........................................10 4.5. SRTCP Packet Format.........................................10
4.6. TESLA MAC...................................................12 4.6. TESLA MAC...................................................12
4.7. PRFs........................................................12 4.7. PRFs........................................................12
5. TESLA Bootstrapping...........................................13 5. TESLA Bootstrapping and Cleanup...............................13
6. SRTP TESLA Default parameters.................................13 6. SRTP TESLA Default parameters.................................13
6.2 Transform-dependent Parameters for TESLA MAC.................14 6.2 Transform-dependent Parameters for TESLA MAC.................14
7. Security Considerations.......................................14 7. Security Considerations.......................................15
8. IANA Considerations...........................................15 8. IANA Considerations...........................................15
9. Acknowledgements..............................................15 9. Acknowledgements..............................................15
10. Author's Addresses...........................................15 10. Author's Addresses...........................................15
11. References...................................................16 11. References...................................................16
1. Introduction 1. Introduction
Multicast and broadcast communication introduce some new security Multicast and broadcast communications introduce some new security
challenges compared to unicast communication. Many multicast and challenges compared to unicast communication. Many multicast and
broadcast applications need "data origin authentication" (DOA), or broadcast applications need "data origin authentication" (DOA), or
"source authentication", in order to guarantee that a received "source authentication", in order to guarantee that a received
message had originated from a given source, and was not manipulated message had originated from a given source, and was not manipulated
during the transmission. In unicast communication, a pairwise during the transmission. In unicast communication, a pairwise
security association between one sender and one receiver can provide security association between one sender and one receiver can provide
data origin authentication using symmetric-key cryptography (such as data origin authentication using symmetric-key cryptography (such as
a message authentication code, MAC). When the communication is a message authentication code, MAC). When the communication is
strictly pairwise, the sender and receiver agree upon a key that is strictly pairwise, the sender and receiver agree upon a key that is
known only to them. known only to them.
skipping to change at page 3, line 16 skipping to change at page 3, line 16
Some applications cannot tolerate source ambiguity and must discern Some applications cannot tolerate source ambiguity and must discern
the true sender from any other group member. A common way to solve the true sender from any other group member. A common way to solve
the problem is by use of asymmetric cryptography, such as digital the problem is by use of asymmetric cryptography, such as digital
signatures. This method, unfortunately, suffers from high overhead, signatures. This method, unfortunately, suffers from high overhead,
in terms of time (to sign and verify) and bandwidth (to convey the in terms of time (to sign and verify) and bandwidth (to convey the
signature in the packet). signature in the packet).
Several schemes have been proposed to provide efficient data origin Several schemes have been proposed to provide efficient data origin
authentication in multicast and broadcast scenarios. The Timed authentication in multicast and broadcast scenarios. The Timed
Efficient Stream loss-tolerant Authentication (TESLA), is one such Efficient Stream loss-tolerant Authentication (TESLA) is one such
scheme. scheme.
This memo specifies TESLA authentication for SRTP. SRTP TESLA can This memo specifies TESLA authentication for SRTP. SRTP TESLA can
provide data origin authentication to RTP applications that use provide data origin authentication to RTP applications that use
group security associations (such as multicast RTP applications) so group security associations (such as multicast RTP applications) so
long as receivers abide by the TESLA security invariants [TESLA]. long as receivers abide by the TESLA security invariants [TESLA].
1.1. Notational Conventions 1.1. Notational Conventions
The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
This specification assumes the reader familiar with both SRTP and This specification assumes the reader familiar with both SRTP and
TESLA. Few of their details are explained in this document, and the TESLA. Few of their details are explained in this document, and the
reader can find them in their respective specifications [RFC3711], reader can find them in their respective specifications, [RFC3711]
[TESLA]. This specification uses the same definitions as TESLA for and [TESLA]. This specification uses the same definitions as TESLA
common terms and assumes that the reader is familiar with the TESLA for common terms and assumes that the reader is familiar with the
algorithms and protocols [TESLA]. TESLA algorithms and protocols [TESLA].
2. SRTP 2. SRTP
The Secure Real-time Transport Protocol (SRTP) [RFC3711] is a The Secure Real-time Transport Protocol (SRTP) [RFC3711] is a
profile of RTP, which can provide confidentiality, message profile of RTP, which can provide confidentiality, message
authentication, and replay protection to the RTP traffic and to the authentication, and replay protection to the RTP traffic and to the
RTP control protocol, the Real-time Transport Control Protocol RTP control protocol, the Real-time Transport Control Protocol
(RTCP). Note, the term SRTP may often used to indicate SRTCP as (RTCP). Note, the term SRTP may often be used to indicate SRTCP as
well. well.
SRTP is a framework that allows new security functions and new SRTP is a framework that allows new security functions and new
transforms to be added. SRTP currently does not define any transforms to be added. SRTP currently does not define any
mechanism to provide data origin authentication for group security mechanism to provide data origin authentication for group security
associations. Fortunately, it is straightforward to add TESLA to associations. Fortunately, it is straightforward to add TESLA to
the SRTP cryptographic framework. the SRTP cryptographic framework.
The TESLA extension to SRTP is defined in this specification, which The TESLA extension to SRTP is defined in this specification, which
assumes that the reader is familiar with the SRTP specification assumes that the reader is familiar with the SRTP specification
[RFC3711], its packet structure, and processing rules. [RFC3711], its packet structure, and processing rules.
3. TESLA 3. TESLA
TESLA provides delayed per-packet data authentication and is TESLA provides delayed per-packet data authentication and is
specified in [TESLA]. This specification assumes that the reader is specified in [TESLA].
familiar with TESLA [TESLA].
In addition to its SRTP data-packet definition given here, TESLA In addition to its SRTP data-packet definition given here, TESLA
needs an initial synchronization protocol and initial bootstrapping needs an initial synchronization protocol and initial bootstrapping
procedure. The synchronization protocol allows the sender and the procedure. The synchronization protocol allows the sender and the
receiver to compare their clocks and determine an upper bound of the receiver to compare their clocks and determine an upper bound of the
difference. The synchronization protocol is outside the scope of difference. The synchronization protocol is outside the scope of
this document. this document.
TESLA also requires an initial bootstrapping procedure to exchange TESLA also requires an initial bootstrapping procedure to exchange
needed parameters and the initial commitment to the key chain needed parameters and the initial commitment to the key chain
[TESLA]. For SRTP, it is assumed that the bootstrapping is [TESLA]. For SRTP, it is assumed that the bootstrapping is
performed out-of-band, possibly using the key management protocol performed out-of-band, possibly using the key management protocol
that is exchanging the security parameters for SRTP, e.g. [GDOI], that is exchanging the security parameters for SRTP, e.g. [GDOI],
[MIKEY]. Initial bootstrapping of TESLA is outside the scope of [RFC3830]. Initial bootstrapping of TESLA is outside the scope of
this document. this document.
4. Usage of TESLA within SRTP 4. Usage of TESLA within SRTP
The present specification is an extension to the SRTP specification The present specification is an extension to the SRTP specification
[RFC3711] and describes the use of TESLA with only a single key [RFC3711] and describes the use of TESLA with only a single key
chain, and the delayed-authentication TESLA elements of procedure chain and delayed-authentication [TESLA].
[TESLA].
4.1. The TESLA extension 4.1. The TESLA extension
TESLA is an OPTIONAL authentication transform for SRTP. When used, TESLA is an OPTIONAL authentication transform for SRTP. When used,
TESLA adds the fields showed in Figure 1 per-packet. The fields TESLA adds the fields shown in Figure 1 per-packet. The fields
added by TESLA are called "TESLA authentication extensions" added by TESLA are called "TESLA authentication extensions"
altogether, whereas "authentication tag" or "integrity protection altogether, whereas "authentication tag" or "integrity protection
tag" indicate the normal SRTP integrity protection tag, when the tag" indicate the normal SRTP integrity protection tag, when the
SRTP master key is shared by more than two endpoints [RFC3711]. SRTP master key is shared by more than two endpoints [RFC3711].
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| I | | i |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Disclosed Key ~ ~ Disclosed Key ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ TESLA MAC ~ ~ TESLA MAC ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: The "TESLA authentication extension". Figure 1: The "TESLA authentication extension".
I: 32 bit, MANDATORY i: 32 bit, MANDATORY
Identifier of the time interval I, corresponding to the key K_i Identifier of the time interval i, corresponding to the key K_i
that is used to calculate the TESLA MAC present in the current that is used to calculate the TESLA MAC present in the current
packet (and in the packets sent in the current time interval I). packet (and in the packets sent in the current time interval i).
Disclosed Key: variable length, MANDATORY Disclosed Key: variable length, MANDATORY
The disclosed key (K_i-d), that can be used to authenticate The disclosed key (K_(i-d)), that can be used to authenticate
previous packets from earlier time intervals [TESLA]. previous packets from earlier time intervals [TESLA].
TESLA MAC (Message Authentication Code): variable length, MANDATORY TESLA MAC (Message Authentication Code): variable length, MANDATORY
The MAC computed using the key K'_i (derived from K_i) [TESLA], The MAC computed using the key K'_i (derived from K_i) [TESLA],
which is disclosed in a subsequent packet (in the Disclosed Key which is disclosed in a subsequent packet (in the Disclosed Key
field). The MAC coverage is defined in Section 4.6. field). The MAC coverage is defined in Section 4.6.
4.2. SRTP Packet Format 4.2. SRTP Packet Format
Figure 2 illustrates the format of the SRTP packet when TESLA is Figure 2 illustrates the format of the SRTP packet when TESLA is
applied. When applied to RTP, the TESLA authentication extension applied. When applied to RTP, the TESLA authentication extension
SHALL be inserted before the (optional) SRTP MKI and (recommended) SHALL be inserted before the (optional) SRTP MKI and (recommended)
authentication tag. authentication tag (SRTP MAC).
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<+<+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<+<+
|V=2|P|X| CC |M| PT | sequence number | | | |V=2|P|X| CC |M| PT | sequence number | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |
| timestamp | | | | timestamp | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |
| synchronization source (SSRC) identifier | | | | synchronization source (SSRC) identifier | | |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ | | +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ | |
| contributing source (CSRC) identifiers | | | | contributing source (CSRC) identifiers | | |
| .... | | | | .... | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |
| RTP extension (OPTIONAL) | | | | RTP extension (OPTIONAL) | | |
+>+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | +>+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |
| | payload ... | | | | | payload ... | | |
| | +-------------------------------+ | | | | +-------------------------------+ | |
| | | RTP padding | RTP pad count | | | | | | RTP padding | RTP pad count | | |
+>+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | +>+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<+ |
| | I | | | | | i | | |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<+ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |
| ~ Disclosed Key ~ | | | ~ Disclosed Key ~ | |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |
| ~ TESLA MAC ~ | | | ~ TESLA MAC ~ | |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<|-+ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<|-+
| ~ MKI ~ | | | | ~ MKI ~ | |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |
| ~ MAC ~ | | | ~ MAC ~ | |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |
| | | | | |
+- Encrypted Portion TESLA Authenticated Portion ---+ | +- Encrypted Portion TESLA Authenticated Portion ---+ |
| |
Authenticated Portion ---+ Authenticated Portion ---+
Figure 2. The format of the SRTP packet when TESLA is applied. Note Figure 2. The format of the SRTP packet when TESLA is applied. Note
that it is OPTIONAL to apply TESLA, i.e. the TESLA fields are that it is OPTIONAL to apply TESLA, i.e. the TESLA fields are
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As in SRTP, the "Encrypted Portion" of an SRTP packet consists of As in SRTP, the "Encrypted Portion" of an SRTP packet consists of
the encryption of the RTP payload (including RTP padding when the encryption of the RTP payload (including RTP padding when
present) of the equivalent RTP packet. present) of the equivalent RTP packet.
The "Authenticated Portion" of an SRTP packet consists of the RTP The "Authenticated Portion" of an SRTP packet consists of the RTP
header, the Encrypted Portion of the SRTP packet, and the TESLA header, the Encrypted Portion of the SRTP packet, and the TESLA
authentication extension. Note that the definition is extended from authentication extension. Note that the definition is extended from
[RFC3711] by the inclusion of the TESLA authentication extension. [RFC3711] by the inclusion of the TESLA authentication extension.
The "TESLA Authenticated Portion" of an SRTP packet consists of the The "TESLA Authenticated Portion" of an SRTP packet consists of the
RTP header, the Encrypted Portion of the SRTP packet, and the TESLA RTP header and the Encrypted Portion of the SRTP packet.
I field.
4.3. Extension of the SRTP Cryptographic Context 4.3. Extension of the SRTP Cryptographic Context
When TESLA is used, the definition of cryptographic context in When TESLA is used, the definition of cryptographic context in
Section 3.2 of SRTP SHALL include the following extensions. Section 3.2 of SRTP SHALL include the following extensions.
Transform-independent Parameter Transform-independent Parameter
a flag indicating the use of TESLA in SRTP. When this bit is set, a flag indicating the use of TESLA in SRTP. When this bit is set,
the following TESLA transform-dependent parameters define the the following TESLA transform-dependent parameters define the
particular TESLA configuration. particular TESLA configuration (see [TESLA] for the TESLA-
parameter definition).
Transform-dependent Parameters Transform-dependent Parameters
1. an identifier for the PRF, f, implementing the one-way function 1. an identifier for the PRF, f, implementing the one-way function
F(x) in TESLA (to derive the keys in the chain), e.g. to F(x) in TESLA (to derive the keys in the chain), e.g. to
indicate HMAC-SHA1, see Section 6.2 for the default value. indicate HMAC-SHA1, see Section 6.2 for the default value.
2. a non-negative integer n_c, determining the length of the F 2. a non-negative integer n_p, determining the length of the F
output, i.e. the length of the keys in the chain (that is also output, i.e. the length of the keys in the chain (that is also
the key disclosed in an SRTP packet), see Section 6.2 for the the key disclosed in an SRTP packet), see Section 6.2 for the
default value. default value.
3. an identifier for the PRF, f', implementing the one-way 3. an identifier for the PRF, f', implementing the one-way
function F'(x) in TESLA (to derive the keys for the TESLA MAC, function F'(x) in TESLA (to derive the keys for the TESLA MAC,
from the keys in the chain), e.g. to indicate HMAC-SHA1, see from the keys in the chain), e.g. to indicate HMAC-SHA1, see
Section 6.2 for the default value. Section 6.2 for the default value.
4. a non-negative integer n_f, determining the length of the 4. a non-negative integer n_f, determining the length of the
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for the default value. for the default value.
6. a non-negative integer n_m, determining the length of the 6. a non-negative integer n_m, determining the length of the
output of the TESLA MAC, see Section 6.2 for the default value. output of the TESLA MAC, see Section 6.2 for the default value.
7. the beginning of the session T_0, 7. the beginning of the session T_0,
8. the interval duration T_int (in msec), 8. the interval duration T_int (in msec),
9. the key disclosure delay d (in number of intervals) 9. the key disclosure delay d (in number of intervals)
10. non-negative integer n_c, determining the length of the key 10. the upper bound D_t (in sec) on the lag of the receiver clock
chain, which is determined based up the expected duration of relative to the sender clock (this quantity has to be
calculated by the peers out-of-band)
11. non-negative integer n_c, determining the length of the key
chain, which is determined based upon the expected duration of
the stream. the stream.
11. the initial key of the chain to which the sender has 12. the initial key of the chain to which the sender has
committed himself. committed himself.
F(x) is used to compute a keychain of keys in SRTP TESLA, as defined F(x) is used to compute a keychain of keys in SRTP TESLA, as defined
in Section 6. Also according to TESLA, F'(x) computes a TESLA MAC in Section 6. Also according to TESLA, F'(x) computes a TESLA MAC
key with inputs as defined in Section 6. key with inputs as defined in Section 6.
Section 6 of this document defines the default values for the Section 6 of this document defines the default values for the
transform-independent and transform-specific TESLA parameters. transform-independent and transform-specific TESLA parameters.
4.4. SRTP Processing 4.4. SRTP Processing
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processing, as the SRTP MAC is checked upon packet arrival for DoS processing, as the SRTP MAC is checked upon packet arrival for DoS
prevention, but the current packet is not TESLA-authenticated. Each prevention, but the current packet is not TESLA-authenticated. Each
packet is buffered until a subsequent packet discloses its TESLA packet is buffered until a subsequent packet discloses its TESLA
key. The TESLA verification itself consists of some steps, such as key. The TESLA verification itself consists of some steps, such as
tests of TESLA security invariants, that are described in Section tests of TESLA security invariants, that are described in Section
3.5-3.7 of [TESLA]. The words "TESLA computation" and "TESLA 3.5-3.7 of [TESLA]. The words "TESLA computation" and "TESLA
verification" hereby imply all those steps, which are not all verification" hereby imply all those steps, which are not all
spelled out in the following. In particular, notice that the TESLA spelled out in the following. In particular, notice that the TESLA
verification implies checking the safety condition (Section 3.5 of verification implies checking the safety condition (Section 3.5 of
[TESLA]). If the safe condition does not hold, the packet MUST be [TESLA]). If the safe condition does not hold, the packet MUST be
discarded. discarded, and the event SHOULD be logged.
4.4.1 Sender Processing 4.4.1 Sender Processing
The sender processing is as described in Section 3.3 of [RFC3711], The sender processing is as described in Section 3.3 of [RFC3711],
up to step 5 included. After that the following process is up to step 5 included. After that the following process is
followed: followed:
6. When TESLA is applied, identify the key in the TESLA chain to be 6. When TESLA is applied, identify the key in the TESLA chain to be
used in the current time interval, and the TESLA MAC key derived used in the current time interval, and the TESLA MAC key derived
from it. Execute the TESLA computation to obtain the TESLA from it. Execute the TESLA computation to obtain the TESLA
authentication extension for the current packet, by appending the authentication extension for the current packet, by appending the
current interval time (as I field), the disclosed key of the chain current interval time (as i field), the disclosed key of the chain
for an earlier packet, and the TESLA MAC under the current key from for an earlier packet, and the TESLA MAC under the current key from
the chain. This step uses the related TESLA parameters from the the chain. This step uses the related TESLA parameters from the
crypto context as for Step 4. crypto context as for Step 4.
7. If the MKI indicator in the SRTP crypto context is set to one, 7. If the MKI indicator in the SRTP crypto context is set to one,
append the MKI to the packet. append the MKI to the packet.
8. When TESLA is applied, compute the authentication tag as 8. When TESLA is applied, and if the SRTP authentication (external
tag) is required (for DoS), compute the authentication tag as
described in step 7 of Section 3.3 of the SRTP specification, but described in step 7 of Section 3.3 of the SRTP specification, but
with coverage as defined in this specification (see Section 4.6). with coverage as defined in this specification (see Section 4.6).
9. If necessary, update the ROC (step 8 in Section 3.3 of 9. If necessary, update the ROC (step 8 in Section 3.3 of
[RFC3711]). [RFC3711]).
4.4.2 Receiver Processing 4.4.2 Receiver Processing
The receiver processing is as described in Section 3.3 of [RFC3711], The receiver processing is as described in Section 3.3 of [RFC3711],
up to step 4 included. up to step 4 included.
To authenticate and replay-protect the current packet, the To authenticate and replay-protect the current packet, the
processing is the following: processing is the following:
First check if the packet has been replayed (as for Section 3.3 of First check if the packet has been replayed (as for Section 3.3 of
[RFC3711]). The SRTP replay list contains SRTP indices of recently [RFC3711]). Note however, the SRTP replay list contains SRTP
received packets that have been authenticated by TESLA. (I.e. indices of recently received packets that have been authenticated
replay list updates MUST NOT be based on SRTP MAC.) If the packet by TESLA (i.e. replay list updates MUST NOT be based on SRTP MAC).
is judged to be replayed, then the packet MUST be discarded, and If the packet is judged to be replayed, then the packet MUST be
the event SHOULD be logged. discarded, and the event SHOULD be logged.
Next, perform verification of the SRTP integrity protection tag Next, perform verification of the SRTP integrity protection tag
(note, not the TESLA MAC), if present, using the rollover counter (note, not the TESLA MAC), if present, using the rollover counter
from the current packet, the authentication algorithm indicated in from the current packet, the authentication algorithm indicated in
the cryptographic context, and the session authentication key. If the cryptographic context, and the session authentication key. If
the verification is unsuccessful, the packet MUST be discarded the verification is unsuccessful, the packet MUST be discarded
from further processing and the event SHOULD be logged. from further processing and the event SHOULD be logged.
If the verification is successful, remove and store the MKI (if If the verification is successful, remove and store the MKI (if
present) and authentication tag fields from the packet. The packet present) and authentication tag fields from the packet. The packet
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extension from the packet. extension from the packet.
To decrypt the current packet, the processing is the following: To decrypt the current packet, the processing is the following:
Decrypt the Encrypted Portion of the packet, using the decryption Decrypt the Encrypted Portion of the packet, using the decryption
algorithm indicated in the cryptographic context, the session algorithm indicated in the cryptographic context, the session
encryption key and salt (if used) found in Step 4 with the index encryption key and salt (if used) found in Step 4 with the index
from Step 2. from Step 2.
(Note that the order of decryption and TESLA verification is not (Note that the order of decryption and TESLA verification is not
mandated. It is up to the application if to perform decryption mandated. It is RECOMMENDED to perform the TESLA verification
immediately after the successful SRTP integrity protection before decryption. TESLA application designers might choose to
verification and then get informed if the TESLA authentication for implement optimistic processing techniques such as notification of
that packet has failed, or if to wait and TESLA- verify the packet TESLA verification results after decryption or even after plaintext
before further processing). processing. Optimistic verification is beyond the scope of this
document.)
Update the rollover counter and highest sequence number, s_l, in the Update the rollover counter and highest sequence number, s_l, in the
cryptographic context, using the packet index estimated in Step 2. cryptographic context, using the packet index estimated in Step 2.
If replay protection is provided, also update the Replay List (i.e., If replay protection is provided, also update the Replay List (i.e.,
the Replay List is updated after the TESLA authentication is the Replay List is updated after the TESLA authentication is
successfully verified). successfully verified).
4.5. SRTCP Packet Format 4.5. SRTCP Packet Format
Figure 3 illustrates the format of the SRTCP packet when TESLA is Figure 3 illustrates the format of the SRTCP packet when TESLA is
applied. The TESLA authentication extension SHALL be inserted applied. The TESLA authentication extension SHALL be inserted
before the MKI and authentication tag. Recall from [RFC3711] that before the MKI and authentication tag. Recall from [RFC3711] that
in SRTCP the MKI is OPTIONAL, while the E-bit, the SRTCP index, and in SRTCP the MKI is OPTIONAL, while the E-bit, the SRTCP index, and
the authentication tag are MANDATORY. the authentication tag are MANDATORY. This means that the SRTP
(external) MAC is MANDATORY also when TESLA is used.
As in SRTP, the "Encrypted Portion" of an SRTCP packet consists of As in SRTP, the "Encrypted Portion" of an SRTCP packet consists of
the encryption of the RTCP payload of the equivalent compound RTCP the encryption of the RTCP payload of the equivalent compound RTCP
packet, from the first RTCP packet, i.e., from the ninth (9) octet packet, from the first RTCP packet, i.e., from the ninth (9) octet
to the end of the compound packet. to the end of the compound packet.
The "Authenticated Portion" of an SRTCP packet consists of the The "Authenticated Portion" of an SRTCP packet consists of the
entire equivalent (eventually compound) RTCP packet, the E flag, the entire equivalent (eventually compound) RTCP packet, the E flag, the
SRTCP index (after any encryption has been applied to the payload), SRTCP index (after any encryption has been applied to the payload),
and the TESLA extension. Note that the definition is extended from and the TESLA extension. Note that the definition is extended from
[RFC3711] by the inclusion of the TESLA authentication extension. [RFC3711] by the inclusion of the TESLA authentication extension.
We define the "TESLA Authenticated Portion" of an SRTCP packet as We define the "TESLA Authenticated Portion" of an SRTCP packet as
consisting of the RTCP header (first 8 bytes), the Encrypted Portion consisting of the RTCP header (first 8 bytes) and the Encrypted
of the SRTCP packet, and the I field. Portion of the SRTCP packet.
Processing of an SRTCP packets is similar to the SRTP processing Processing of an SRTCP packets is similar to the SRTP processing
(Section 4.3), but there are SRTCP-specific changes described in (Section 4.3), but there are SRTCP-specific changes described in
Section 3.4 of the SRTP specification [RFC3711] and in Section 4.6 Section 3.4 of the SRTP specification [RFC3711] and in Section 4.6
of this memo. of this memo.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<+<+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<+<+
|V=2|P| RC | PT=SR or RR | length | | | |V=2|P| RC | PT=SR or RR | length | | |
skipping to change at page 11, line 29 skipping to change at page 11, line 31
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |
| |V=2|P| SC | PT=SDES=202 | length | | | | |V=2|P| SC | PT=SDES=202 | length | | |
| +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ | | | +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ | |
| | SSRC/CSRC_1 | | | | | SSRC/CSRC_1 | | |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |
| ~ SDES items ~ | | | ~ SDES items ~ | |
| +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ | | | +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ | |
| ~ ... ~ | | | ~ ... ~ | |
+>+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ | | +>+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ | |
| |E| SRTCP index | | | | |E| SRTCP index | | |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |
| | I | | |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<+ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<+ |
| | i | | |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |
| ~ Disclosed Key ~ | | | ~ Disclosed Key ~ | |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |
| ~ TESLA MAC ~ | | | ~ TESLA MAC ~ | |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<|-+ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<|-+
| ~ SRTCP MKI ~ | | | ~ SRTCP MKI ~ | |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |
| : authentication tag : | | | : authentication tag : | |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |
| | | | | |
+-- Encrypted Portion TESLA Authenticated Portion -----+ | +-- Encrypted Portion TESLA Authenticated Portion -----+ |
skipping to change at page 12, line 9 skipping to change at page 12, line 9
Authenticated Portion -------+ Authenticated Portion -------+
Figure 3. The format of the SRTCP packet when TESLA is applied. Figure 3. The format of the SRTCP packet when TESLA is applied.
Note that it is OPTIONAL to apply TESLA, i.e. the TESLA fields are Note that it is OPTIONAL to apply TESLA, i.e. the TESLA fields are
OPTIONAL. OPTIONAL.
4.6. TESLA MAC 4.6. TESLA MAC
Let M' denote packet data to be TESLA-authenticated. In the case of Let M' denote packet data to be TESLA-authenticated. In the case of
SRTP, M' SHALL consist of the SRTP TESLA Authenticated Portion (RTP SRTP, M' SHALL consist of the SRTP TESLA Authenticated Portion (RTP
header, SRTP Encrypted Portion, and I field) shown in Figure 1 or header and SRTP Encrypted Portion, see Figure 2) of the packet
Figure 2) of the packet concatenated with the ROC of the same concatenated with the ROC of the same packet:
packet:
M' = ROC || TESLA Authenticated Portion. M' = ROC || TESLA Authenticated Portion.
In the case of SRTCP, M' SHALL consist of the SRTCP TESLA In the case of SRTCP, M' SHALL consist of the SRTCP TESLA
Authenticated Portion only (RTCP header, SRTCP Encrypted Portion, Authenticated Portion only (RTCP header and SRTCP Encrypted
and I field). Portion).
The normal authentication tag SHALL be applied with the same The normal authentication tag (OPTIONAL for SRTP, MANDATORY for
coverage as specified in [RFC3711], i.e.: SRTCP) SHALL be applied with the same coverage as specified in
[RFC3711], i.e.:
- for SRTP: Authenticated Portion || ROC (with the extended - for SRTP: Authenticated Portion || ROC (with the extended
definition of SRTP Authentication Portion as for Section 4.2) definition of SRTP Authentication Portion as for Section 4.2)
- for SRTCP: Authenticated Portion (with the extended definition of - for SRTCP: Authenticated Portion (with the extended definition of
SRTCP Authentication Portion as for Section 4.2). SRTCP Authentication Portion as for Section 4.2).
The pre-defined authentication transform in SRTP, HMAC-SHA1 The pre-defined authentication transform in SRTP, HMAC-SHA1
[RFC2104], is also used to generate the TESLA MAC. For SRTP [RFC2104], is also used to generate the TESLA MAC. For SRTP
(respectively SRTCP), the HMAC SHALL be applied to the key in the (respectively SRTCP), the HMAC SHALL be applied to the key in the
skipping to change at page 13, line 5 skipping to change at page 13, line 5
* one one-way function F(x) to derive the key chain, and * one one-way function F(x) to derive the key chain, and
* one one-way function F'(x) to derive (from each key of the chain) * one one-way function F'(x) to derive (from each key of the chain)
the key that is actually used to calculate the TESLA MAC. the key that is actually used to calculate the TESLA MAC.
When TESLA is used within SRTP, the default choice of the two PRFs When TESLA is used within SRTP, the default choice of the two PRFs
SHALL be HMAC-SHA1. Default values are in Section 6.2. SHALL be HMAC-SHA1. Default values are in Section 6.2.
Other PRFs can be chosen, and their use SHALL follow the common Other PRFs can be chosen, and their use SHALL follow the common
guidelines in [RFC3711] when adding new security parameters. guidelines in [RFC3711] when adding new security parameters.
5. TESLA Bootstrapping 5. TESLA Bootstrapping and Cleanup
The extensions to the SRTP cryptographic context include a set of The extensions to the SRTP cryptographic context include a set of
TESLA parameters that are listed in section 4.3 of this document. TESLA parameters that are listed in section 4.3 of this document.
Furthermore, TESLA MUST be bootstrapped at session set-up (for the Furthermore, TESLA MUST be bootstrapped at session set-up (for the
parameter exchange and the initial key commitment) through a regular parameter exchange and the initial key commitment) through a regular
data authentication system (a digital signature algorithm is data authentication system (a digital signature algorithm is
RECOMMENDED). Key management procedures can take care of this RECOMMENDED). Key management procedures can take care of this
bootstrapping prior to the commencement of an SRTP session where bootstrapping prior to the commencement of an SRTP session where
TESLA authentication is used. The bootstrapping mechanism is out of TESLA authentication is used. The bootstrapping mechanism is out of
scope for this document. scope for this document (it could for example be part of the key
management protocol).
A critical factor for the security of TESLA is that the sender and A critical factor for the security of TESLA is that the sender and
receiver need to be loosely synchronized. TESLA assumes that the receiver need to be loosely synchronized. TESLA requires a bound on
local internal clocks do not drift too much during the session. Use clock drift to be known (D_t). Use of TESLA in SRTP assumes that
of TESLA in SRTP assumes that the time synchronization is guaranteed the time synchronization is guaranteed by out-of-band schemes (e.g.
by out-of-band schemes (e.g. key management), i.e. it is not in the key management), i.e. it is not in the scope of SRTP.
scope of SRTP.
It is also important to realize that TESLA has some reliability
requirements in that a key is disclosed for a packet in a subsequent
packet, which can get lost. Since a key is repeated across packets
in an interval, TESLA is robust to packet loss. This repetition
might abruptly stop, however, if the key-bearing packets stop
abruptly at the end of the stream. To avoid this nasty boundary
condition, send null packets with TESLA keys for one entire interval
following the interval in which the stream ceases.
6. SRTP TESLA Default parameters 6. SRTP TESLA Default parameters
Key management procedures establish SRTP TESLA operating parameters Key management procedures establish SRTP TESLA operating parameters
listed in section 4.3 of this document. The operating parameters listed in section 4.3 of this document. The operating parameters
appear in the SRTP cryptographic context and have the following appear in the SRTP cryptographic context and have the following
default values. In the future, an Internet RFC MAY define default values. In the future, an Internet RFC MAY define
alternative settings for SRTP TESLA that are different than those alternative settings for SRTP TESLA that are different than those
specified here. In particular, it should be noted that the settings specified here. In particular, it should be noted that the settings
defined in this memo can have a large impact on bandwidth, as it defined in this memo can have a large impact on bandwidth, as it
skipping to change at page 15, line 9 skipping to change at page 15, line 18
are discussed in [PCST]. TESLA requires receiver's buffering before are discussed in [PCST]. TESLA requires receiver's buffering before
authentication, therefore the receiver can suffer a denial of authentication, therefore the receiver can suffer a denial of
service attack due to a flood of bogus packets. To address this service attack due to a flood of bogus packets. To address this
problem, the current specification REQUIRES the use of a 32-bit SRTP problem, the current specification REQUIRES the use of a 32-bit SRTP
MAC in addition to TESLA MAC. The shorter size of the SRTP MAC is MAC in addition to TESLA MAC. The shorter size of the SRTP MAC is
here motivated by the fact that that MAC served purely for DoS here motivated by the fact that that MAC served purely for DoS
prevention from attackers external to the group. prevention from attackers external to the group.
The use of TESLA in SRTP defined in this specification is subject to The use of TESLA in SRTP defined in this specification is subject to
the security considerations discussed in the SRTP specification the security considerations discussed in the SRTP specification
[RFC3711] an in the TESLA specification [TESLA]. In particular, it [RFC3711] and in the TESLA specification [TESLA]. In particular, the
must be noted that the all TESLA security is dependent on the TESLA security is dependent on the computation of the "safety
computation of the "safety condition" as defined in Section 3.5 of condition" as defined in Section 3.5 of [TESLA].
[TESLA].
SRTP TESLA depends on the effective security of the systems that SRTP TESLA depends on the effective security of the systems that
perform bootstrapping (time synchronization) and key management. perform bootstrapping (time synchronization) and key management.
These systems are external to SRTP and are not considered in this These systems are external to SRTP and are not considered in this
specification. specification.
8. IANA Considerations 8. IANA Considerations
No IANA registration is required. No IANA registration is required.
9. Acknowledgements 9. Acknowledgements
The authors would like to thanks Ran Canetti, Karl Norrman, Mats The authors would like to thanks Ran Canetti, Karl Norrman, Mats
N„slund, and Fredrik Lindholm for their valuable help. N„slund, Fredrik Lindholm, David McGrew, and Bob Briscoe for their
valuable help.
10. Author's Addresses 10. Author's Addresses
Questions and comments should be directed to the authors and Questions and comments should be directed to the authors and
msec@ietf.org: msec@ietf.org:
Mark Baugher Mark Baugher
Cisco Systems, Inc. Cisco Systems, Inc.
5510 SW Orchid Street Phone: +1 408-853-4418 5510 SW Orchid Street Phone: +1 408-853-4418
Portland, OR 97219 USA Email: mbaugher@cisco.com Portland, OR 97219 USA Email: mbaugher@cisco.com
skipping to change at page 16, line 21 skipping to change at page 16, line 25
Distributed System Security Symposium NDSS 2001, pp. 35-46, 2001. Distributed System Security Symposium NDSS 2001, pp. 35-46, 2001.
[RFC1305] Mills D., Network Time Protocol (Version 3) [RFC1305] Mills D., Network Time Protocol (Version 3)
Specification, Implementation and Analysis, RFC 1305, March, 1992. Specification, Implementation and Analysis, RFC 1305, March, 1992.
http://www.ietf.org/rfc/rfc1305.txt http://www.ietf.org/rfc/rfc1305.txt
[RFC3711] Baugher, McGrew, Naslund, Carrara, Norrman, "The Secure [RFC3711] Baugher, McGrew, Naslund, Carrara, Norrman, "The Secure
Real-time Transport Protocol", RFC 3711, March 2004. Real-time Transport Protocol", RFC 3711, March 2004.
[TESLA] Perrig, Canetti, Song, Tygar, Briscoe, "TESLA: Multicast [TESLA] Perrig, Canetti, Song, Tygar, Briscoe, "TESLA: Multicast
Source Authentication Transform Introduction", October 2002, draft- Source Authentication Transform Introduction", August 2004, draft-
ietf-msec-tesla-intro-02.txt. ietf-msec-tesla-intro-03.txt.
Informative Informative
[gkmarch] Baugher, Canetti, Dondeti, Lindholm, "MSEC Group Key [gkmarch] Baugher, Canetti, Dondeti, Lindholm, "MSEC Group Key
Management Architecture", June 2004, <draft-ietf-msec-gkmarch- Management Architecture", June 2004, <draft-ietf-msec-gkmarch-
08.txt>. 08.txt>.
[GDOI] Baugher, Weis, Hardjono, Harney, "The Group Domain of [GDOI] Baugher, Weis, Hardjono, Harney, "The Group Domain of
Interpretation", RFC 3547, July 2003. Interpretation", RFC 3547, July 2003.
[MIKEY] Arkko et al., "MIKEY: Multimedia Internet KEYing", December [RFC3830] Arkko et al., "MIKEY: Multimedia Internet KEYing",
2003, <draft-ietf-msec-mikey-08.txt> December 2003, RFC 3830, August 2004.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2004). This document is subject Copyright (C) The Internet Society (2004). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights. except as set forth therein, the authors retain all their rights.
Disclaimer of Validity Disclaimer of Validity
This document and the information contained herein are provided on This document and the information contained herein are provided on
an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE
REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE
INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
This draft expires in January 2005. This draft expires in April 2005.
 End of changes. 

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