MSEC Working Group B. Weis
Internet-Draft S. Rowles
Intended status: Standards Track Cisco Systems
Expires: September 7, 2009 March 6, 2009
Updates to the Group Domain of Interpretation (GDOI)
draft-ietf-msec-gdoi-update-04
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Abstract
This memo describes updates to the Group Domain of Interpretation
(GDOI) . It provides clarification where the original text is
unclear. It also includes adds several new algorithm attribute
values, including complete support for algorithm agility.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1. Requirements notation . . . . . . . . . . . . . . . . . . 5
2. RFC 3547 Clarification . . . . . . . . . . . . . . . . . . . . 6
2.1. SA KEK Payload . . . . . . . . . . . . . . . . . . . . . . 6
2.2. SA TEK Payload . . . . . . . . . . . . . . . . . . . . . . 6
2.3. KD Payload . . . . . . . . . . . . . . . . . . . . . . . . 7
2.4. SEQ Payload . . . . . . . . . . . . . . . . . . . . . . . 7
2.5. POP Payload . . . . . . . . . . . . . . . . . . . . . . . 8
2.6. CERT Payload . . . . . . . . . . . . . . . . . . . . . . . 8
2.7. SIG Payload . . . . . . . . . . . . . . . . . . . . . . . 8
2.8. KE Payload . . . . . . . . . . . . . . . . . . . . . . . . 8
2.9. Attribute behavour . . . . . . . . . . . . . . . . . . . . 9
2.10. Deletion of SAs . . . . . . . . . . . . . . . . . . . . . 9
3. Authorization . . . . . . . . . . . . . . . . . . . . . . . . 10
4. Harmonization with RFC 5374 . . . . . . . . . . . . . . . . . 12
4.1. Group Security Policy Database Attributes . . . . . . . . 12
4.1.1. Address Preservation . . . . . . . . . . . . . . . . . 12
4.1.2. SA Direction . . . . . . . . . . . . . . . . . . . . . 12
4.1.3. Re-key rollover . . . . . . . . . . . . . . . . . . . 13
5. New GDOI Attributes . . . . . . . . . . . . . . . . . . . . . 14
5.1. Signature Hash Algorithm . . . . . . . . . . . . . . . . . 14
5.2. Support of AH . . . . . . . . . . . . . . . . . . . . . . 14
5.3. Group Associated Policy . . . . . . . . . . . . . . . . . 16
5.3.1. ACTIVATION_TIME_DELAY . . . . . . . . . . . . . . . . 17
5.3.2. DEACTIVATION_TIME_DELAY . . . . . . . . . . . . . . . 17
5.3.3. SENDER_ID . . . . . . . . . . . . . . . . . . . . . . 17
5.3.3.1. GCKS Semantics . . . . . . . . . . . . . . . . . . 18
5.3.3.2. Group Member Semantics . . . . . . . . . . . . . . 18
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
7. Security Considerations . . . . . . . . . . . . . . . . . . . 21
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 22
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9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23
9.1. Normative References . . . . . . . . . . . . . . . . . . . 23
9.2. Informative References . . . . . . . . . . . . . . . . . . 23
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 25
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1. Introduction
The Group Domain of Interpretation (GDOI) [RFC3547] is a group key
management protocol fitting into the Multicast Security Group Key
Management Architecture [RFC4046]. GDOI is used to disseminate
policy and corresponding secrets to a group of participants. GDOI is
implemented on hosts and intermediate systems to protect group IP
communication (e.g., IP multicast packets) by encapsulating them with
the IP Encapsulating Security Payload (ESP) [RFC4303] packets.
Several factors have prompted new for updates to GDOI including:
o the discovery of inconsistencies in RFC 3547, which need
clarification (Section 2),
o the publishing of an attack on the protocol (Section 3)
o the publishing of the Multicast Extensions to the Security
Architecture for the Internet Protocol [RFC5374], which has
implications to the policy distributed by group key management
(Section 4),
o the need for new GDOI algorithm attributes, including the need to
support SHA-256 [FIPS.180-2.2002] as an alternative to the SHA-1
and MD5 hash algorithms (Section 5).
The clarification and modifications in this memo update RFC 3547.
1.1. Requirements notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
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2. RFC 3547 Clarification
Implementation experience of RFC 3547 has revealed a few areas of
text that are not sufficiently precise. This section provides
clarifying text for those areas.
2.1. SA KEK Payload
Section 5.3 of RFC 4357 defines the SA KEK payload. It includes the
"POP Key Length" field,The units of this field are not explicitly
specified in RFC 3547. The value MUST be a number representing the
length of key in bits. In the case of POP_ALG_RSA, the value
represents the size of the modulus.
Section 5.3 of RFC 4357 also defines the POP Algorithm of type of
POP_ALG_RSA, but does not specify which PKCS#1 [RFC3447] encoding
method is employed. To match existing practice, this memo requires
that it be the EMSA-PKCS1-v1_5 encoding method.
The units of the SIG_KEY_LENGTH KEK attribute value was not
explicitly specified in section 5.3.8 of RFC 3547. The value MUST be
a number representing the length of the KEK encryption key in bits.
The Group Controller/Key Server (GCKS) adds the KEK_KEY_LEN attribute
to the SA payload when distributing KEK policy to group members. The
group member verifies whether or not it has the capability of using a
cipher key of that size. If the cipher definition includes a fixed
key length (e.g., KEK_ALG_3DES), the group member can make its
decision solely using KEK_ALGORITHM attribute and does not need the
KEK_KEY_LEN attribute. Sending the KEK_KEY_LEN attribute in the SA
payload is OPTIONAL if the KEK cipher has a fixed key length.
Minimum attributes that must be sent as part of an SA KEK:
KEK_ALGORITHM, KEK_KEY_LENGTH (if the cipher definition includes a
variable length key), KEK_KEY_LIFETIME, SIG_HASH_ALGORITHM (except
for DSA based algorithms), SIG_ALGORITHM, and SIG_KEY_LENGTH.
2.2. SA TEK Payload
Section 5.4.1 of RFC 3547 states that all mandatory IPsec DOI
attributes are mandatory in GDOI_PROTO_IPSEC_ESP. However, RFC 2407
lists no such list of mandatory IPsec DOI attributes. This memo
requires that the following attributes MUST be supported by an RFC
3547 implementation supporting the GDOI_PROTO_IPSEC_ESP SA TEK: SA
Life Type, SA Life Duration, Encapsulation Mode, Authentication
Algorithm (if the ESP transform includes authentication).
The GDOI_PROTO_IPSEC_ESP attribute is sometimes referred to in RFC
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3547 by the truncated name of PROTO_IPSEC_ESP.
2.3. KD Payload
Section 5.5.2.1 of RFC 3547 explicitly specifies that if a KEK cipher
requires an IV, then the IV must precede the key in the
KEK_ALGORITHM_KEY KD payload attribute. However, it should be noted
that this IV length is not included in the KEK_KEY_LEN SA payload
attribute sent in the SA payload. The KEK_KEY_LEN includes only the
actual length of the cipher key.
Section 5.5.1.2 of RFC 3547 defines key lengths for the
TEK_INTEGRITY_KEY. When the algorithm passes in the SA TEK payload
is SHA256, keys will consist of 256 bits.
2.4. SEQ Payload
Section 3.2 of RFC 3547 defines a GROUPKEY-PULL message as including
a sequence number, which provides anti-replay state associated with a
KEK. The SEQ payload has no other use, and is omitted from the
GROUPKEY-PULL exchange when a KEK attribute is not included in the SA
payload.
A KEK sequence number is associated with a single SPI (i.e., the
single set of cookie pair values sent in a GROUPKEY-PUSH ISAKMP
[RFC2408] HDR). When a new KEK is distributed by a GCKS, it contains
a new SPI and resets the sequence number.
When a SEQ payload is included in the GROUPKEY-PULL exchange, it
includes the most recently used sequence number for the group. At
the conclusion of a GROUPKEY-PULL exchange, the initiating group
member MUST NOT accept any rekey message with both the KEK attribute
SPI value and a sequence number less than or equal to the one
received during the GROUPKEY-PULL. When the first group member
initiates a GROUPKEY-PULL exchange, the GCKS provides a Sequence
Number of zero, since no GROUPKEY-PUSH messages have yet been sent.
Note the sequence number increments only with GROUPKEY-PUSH messages.
The GROUPKEY-PULL exchange distributes the current sequence number to
the group member.
The sequence number resets to a value of one with a new KEK
attribute. As described in section 5.6 of RFC 3547: "Thus the first
packet sent for a given Rekey SA will have a Sequence Number of 1".
The sequence number increments with each successive rekey.
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2.5. POP Payload
RFC 3547 defines the Proof of Possession (POP) payload, which
contains a digital signature over a hash. Some RFC 3547 text
erroneously describes it as a "prf()".
RFC 3547 omitted including a method of specifying the hash function
type used in the POP payload. As a result, the GCKS or group member
do not have a means by which to agree which hash algorithm should be
used. To remedy this omission without changing the protocol, this
memo specifies that the hash algorithm passed in the
SIG_HASH_ALGORITHM MUST be also used as the POP hash algorithm.
2.6. CERT Payload
Receivers of the POP payload need the sender's public key in order to
validate the POP. However the source of that public key is not
explicitly defined. For example, if the certificate encoding value
passed in the CERT payload (defined in Section 3.9 of RFC 2408) does
not contain a public key then no public key is available. To remedy
this omission, this memo specifies that the certificate passed in the
CERT payload MUST be a public key certificate.
2.7. SIG Payload
The GROUPKEY-PUSH message defined in Section 4 of RFC 3547 includes a
SIG payload. The first paragraph on page 12 is amended as follows.
The SIG payload includes a signature of a hash of the entire
GROUPKEY-PUSH message (excepting the SIG payload bytes) before it
has been encrypted. The HASH is taken over the string 'rekey',
the GROUPKEY-PUSH HDR, SEQ, SA, KD, and optionally the CERT
payload. The prefixed string ensures that the signature of the
Rekey datagram cannot be used for any other purpose in the GDOI
protocol. After the SIG payload is created using the signature of
the above hash, the current KEK encryption key encrypts all the
payloads following the GROUPKEY-PUSH HDR. Note: The rationale for
this order of operations is given in Section 6.3.5 of RFC 3547.
Section 5.3.7.1 of RFC 4357 defines a SIG_ALGORITHM type of
SIG_ALG_RSA, but it omits specifying which PKCS#1 [RFC3447] encoding
method is employed. To match existing practice, this memo requires
that it be the EMSA-PKCS1-v1_5 encoding method.
2.8. KE Payload
The purpose of the KE Payload in GDOI is to encrypt keying material
before encrypting the entire GDOI registration message. However, the
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specification for computing keying material for the additional
encryption function in RFC 3547 is faulty. Furthermore, it has been
observed that because the GDOI registration message uses strong
ciphers and provides authenticated encryption, additional encryption
of the keying material in a GDOI registration message provides
negligible value. Therefore, the use of KE payloads is deprecated in
this memo.
2.9. Attribute behavour
An GDOI implementation MUST abort if it encounters and attribute or
capability that it does not understand.
2.10. Deletion of SAs
RFC 3547 provides for the condition that the GCKS may want to signal
to receivers to delete their SAs, but there may be circumstances
where the GCKS may want to start over with a clean slate. If the
administrator is no longer confident in the integrity of the group,
the GCKS can signal deletion of all policy of a particular TEK
protocol by sending a TEK with a SPI value equal to zero in the
delete payload. For example, if the GCKS wishes to remove all the
KEKs and all the TEKs in the group, the GCKS SHOULD send a delete
payload with a spi of zero and a protocol_id of a TEK protocol_id
value as defined in section 5.4 of RFC 3547, followed by another
delete payload with a spi of zero and a protocol_id of zero,
indicating that the KEK SA should be deleted.
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3. Authorization
Meadows and Pavlovic have published a paper [MP04] describing a means
by which a rogue GDOI device (i.e., GCKS or group member) can gain
access to a group for which it is not a group member. The rogue
device perpetrates a man-in-the-middle attack, which can occur if the
following conditions are true:
1. The rogue GDOI participant convinces an authorized member of the
group (i.e., victim group member) that it is a GCKS for that
group, and it also convinces the GCKS (i.e., victim GCKS) of that
group it is an authorized group member.
2. The victim group member, victim GCKS, and rogue group member all
share IKEv1 authentication credentials.
3. The victim GCKS does not properly verify that the IKE
authentication credentials used to protect a GROUPKEY-PULL
protocol are authorized to be join the group.
The value of proof-of-possession is to prove that the owner of the
identity associated with the Phase 1 key is the same as the owner of
the key distributed in the CERT. This attack can be mitigated by
adding the Phase 1 identities into the hashed data. This memo
replaces the method computing POP_HASH in Section 5.7 of RFC 3547
with the following method:
POP_HASH = hash("pop" | IKE-Initiator-P1-ID | IKE-Responder-P1-ID |
Ni | Nr)
where the fields are hashed as follows:
o The string "pop" without a NULL termination character.
o The IKE Phase 1 identity of the GCKS as distributed in the
"identification Data" portion of the ID payload. Because the
length of the identity is variable, the length of the
Identification Data MUST be hashed as a four octet value with the
length located in the least significant bits (in network byte
order). The length value is hashed before the data value.
o The IKE Phase 1 identity of the group member as distributed in the
"identification Data" portion of the ID payload. Because the
length of the identity is variable, the length of the
Identification Data MUST be hashed as a four octet value with the
length located in the least significant bits (in network byte
order). The length value is hashed before the data value.
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o The initiator nonce Ni, as passed in the first GROUPKEY-PULL
message.
o The responder nonce Nr, as passed in the second GROUPKEY-PULL
message.
This attack can also be mitigated by applying appropriate GCKS and
group member authorization. When the use of CERT and POP payloads
are not mandated in group policy, the GCKS SHOULD have a means of
recognizing authorized group members for each group, where the
recognition is based on IKE authentication credentials. For example,
the GCKS may have a list of authorized IKE identifiers stored for
each Group. The authorization check SHOULD be made after receipt of
the ID payload containing a group id the group member is requesting
to join.
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4. Harmonization with RFC 5374
the Multicast Extensions to the Security Architecture for the
Internet Protocol (RFC 5374) introduces new requirements for a group
key management system distributing IPsec policy. The following
sections describe new GDOI requirements that result from harmonizing
with that document.
4.1. Group Security Policy Database Attributes
RFC 5374 describes new attributes as part of the Group Security
Policy Database (GSPD). These attributes describe policy that a
group key management system must convey to a group member in order to
support those extensions. The GDOI SA TEK payload distributes IPsec
policy using IPsec security association attributes defined in
[ISAKMP-REG]. This section defines how GDOI can convey the new
attributes as IPsec Security Association Attributes.
4.1.1. Address Preservation
Applications use the extensions in RFC 5374 create encapsulate IPsec
multicast packets that are IP multicast packets. In order for the
GDOI group member to appropriately setup the GSPD, the GCKS must
provide that policy to the group member.
Depending on group policy, several address preservation methods are
possible: no address preservation ("None"), preservation of the
original source address ("Source-Only"), preservation of the original
destination address ("Destination-Only"), or both addresses ("Source-
And-Destination"). This memo adds the "Address Preservation"
security association attribute. If this attribute is not included in
a GDOI SA TEK payload provided by a GCKS, then Source-And-Destination
address preservation has been defined for the SA TEK.
4.1.2. SA Direction
Depending on group policy, an IPsec SA created from an SA TEK payload
may be required in one or both directions. SA TEK policy used by
multiple senders is required to be installed in both the sending and
receiving direction ("Symmetric"), whereas SA TEK for a single sender
should only be installed in the receiving direction by receivers
("Receiver-Only") and in the sending direction by the sender
("Sender-Only"). This memo adds the "SA Direction" security
association attribute. If the attribute is not included in a GDOI SA
TEK payload, then the IPsec SA is treated as a Symmetric IPsec SA.
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4.1.3. Re-key rollover
Section 4.2.1 of RFC 5374 specifies a key rollover method that
requires two values be given it from the group key management
protocol. The Activation Time Delay (ATD) attribute allows the GCKS
to specify how long a after the start of a re-key event that a group
member is to activate new TEKs. The Deactivation Time Delay (DTD)
attribute allows the GCKS to specify how long a after the start of a
re-key event that a group member is to deactivate existing TEKs.
This memo adds new attributes by which a GCKS can relay these values
to group members as part of the Group Associated Policy described in
Section 5.
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5. New GDOI Attributes
This section contains new attributes to be are defined as part of
GDOI.
5.1. Signature Hash Algorithm
RFC 3547 defines two signature hash algorithms (MD5 and SHA-1).
However, steady advances in technology have rendered both hash
algorithms to be weak when used as a signature hash algorithm.
The SHA-256 algorithm [FIPS.180-2.2002] has been made available by
NIST as a replacement for SHA-1, and is its preferred replacement for
both MD5 and SHA-1. A new value for the GDOI SIG_HASH_ALGORITHM
attribute is defined by this memo to represent the SHA-256 algorithm:
SIG_HASH_SHA256. Support for SIG_HASH_SHA256 is OPTIONAL.
5.2. Support of AH
RFC3547 only specifies data-security SAs for one security protocol,
IPsec ESP. Typically IPsec implementations use ESP and AH IPsec SAs.
This document extends the capability of GDOI to support both ESP and
AH. The GROUPKEY-PULL mechanism will establish IPsec ESP SAs and
IPsec AH SAs. The GROUPKEY-PUSH will refresh the IPsec ESP SAs and
the IPsec AH SAs. Support for AH [RFC4302] is achieved with the
introduction of a new SA_TEK Protocol-ID with the name
GDOI_PROTO_IPSEC_AH. Support for the GDOI_PROTO_IPSEC_AH SA TEK is
OPTIONAL.
The TEK Protocol-Specific payload for AH is as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
! Protocol ! SRC ID Type ! SRC ID Port !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
!SRC ID Data Len! SRC Identification Data ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
! DST ID Type ! DST ID Port !DST ID Data Len!
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
! DST Identification Data ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
! Transform ID ! SPI !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
! SPI ! RFC 2407 SA Attributes ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
The SAT Payload fields are defined as follows:
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o Protocol (1 octet) -- Value describing an IP protocol ID (e.g.,
UDP/TCP). A value of zero means that the Protocol field should be
ignored.
o SRC ID Type (1 octet) -- Value describing the identity information
found in the SRC Identification Data field. Defined values are
specified by the IPsec Identification Type section in the IANA
ISAKMP Registry [ISAKMP-REG].
o SRC ID Port (2 octets) -- Value specifying a port associated with
the source Id. A value of zero means that the SRC ID Port field
should be ignored.
o SRC ID Data Len (1 octet) -- Value specifying the length of the
SRC Identification Data field.
o SRC Identification Data (variable length) -- Value, as indicated
by the SRC ID Type. Set to three bytes of zero for multiple-
source multicast groups that use a common TEK for all senders.
o DST ID Type (1 octet) -- Value describing the identity information
found in the DST Identification Data field. Defined values are
specified by the IPsec Identification Type section in the IANA
ISAKMP Registry [ISAKMP-REG].
o DST ID Port (1 octet) -- Value describing an IP protocol ID (e.g.,
UDP/TCP). A value of zero means that the DST Id Port field should
be ignored.
o DST ID Port (2 octets) -- Value specifying a port associated with
the source Id. A value of zero means that the DST ID Port field
should be ignored.
o DST ID Data Len (1 octet) -- Value specifying the length of the
DST Identification Data field.
o DST Identification Data (variable length) -- Value, as indicated
by the DST ID Type.
o Transform ID (1 octet) -- Value specifying which AH transform is
to be used. The list of valid values is defined in the IPsec AH
Transform Identifiers section of the IANA ISAKMP Registry
[ISAKMP-REG].
o SPI (4 octets) -- Security Parameter Index for AH.
o RFC 2407 Attributes -- AH Attributes from Section 4.5 of
[RFC2407]. The GDOI supports all IPsec DOI SA Attributes for
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GDOI_PROTO_IPSEC_AH excluding the Group Description, which MUST
NOT be sent by a GDOI implementation and is ignored by a GDOI
implementation if received. The Authentication Algorithm
attribute of the IPsec DOI is group authentication in GDOI. The
following RFC 2407 attributes MUST be sent as part of a
GDOI_PROTO_IPSEC_AH attribute: SA Life Type, SA Life Duration,
Encapsulation Mode.
5.3. Group Associated Policy
RFC 3547 provides for the distribution of policy in the GROUPKEY-PULL
exchange in an SA payload. Policy can define GROUPKEY-PUSH policy
(SA KEK) or traffic encryption policy (SA TEK) such as IPsec policy.
There is a need to distribute group policy that fits into neither
category. Some of this policy is generic to the group, and some is
sender-specific policy for a particular group member.
GDOI distributes this associated group policy in a new payload called
the SA Group Associated Policy (SA SAP). The SA GAP payload follows
any SA KEK payload, and is placed before any SA TEK payloads. In the
case that group policy does not include an SA KEK, the SA Attribute
Next Payload field in the SA payload MAY indicate the SA GAP payload.
The SA GAP payload is defined as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
! Next Payload ! RESERVED ! Payload Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
! Group Associated Policy Attributes ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
The SA GAP payload fields are defined as follows:
o Next Payload (1 octet) -- Identifies the next payload present in
the GROUPKEY-PULL or the GROUPKEY-PUSH message. The only valid
next payload type for this message is an SA TEK or zero to
indicate there are no more security association attributes.
o RESERVED (1 octet) -- Must be zero.
o Payload Length (2 octets) -- Length of this payload, including the
SA GAP header and Attributes.
o Group Associated Policy Attributes (variable) -- Contains
attributes following the format defined in Section 3.3 of RFC
2408.
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Several group associated policy attributes are defined in this memo.
5.3.1. ACTIVATION_TIME_DELAY
This attribute allows a GCKS to set the Activation Time Delay for SAs
generated from TEKs. The value is in seconds. If a group member
receives a TEK with an ATD value, but discovers that it has no
current SAs matching the policy in the TEK, then it SHOULD create and
install SAs from the TEK immediately.
5.3.2. DEACTIVATION_TIME_DELAY
This attribute allows a GCKS to set the Deactivation Time Delay for
SAs generated from TEKs. The value is in seconds.
5.3.3. SENDER_ID
Several new AES counter-based modes of operation have been specified
for ESP [RFC3686],[RFC4106],[RFC4309],[RFC4543] and AH [RFC4543].
These AES counter-based modes require that no two senders in the
group ever send a packet with the same IV. This requirement can be
met using the method described in
[I-D.ietf-msec-ipsec-group-counter-modes], which requires each sender
to be allocated a unique Sender ID (SID). The SENDER_ID attribute is
used to distribute a SID to a group member during the GROUPKEY-PULL
message. Other algorithms with the same need may be defined in the
future; the sender MUST use the IV construction method described
above with those algorithms as well.
The SENDER_ID attribute value contains the following fields.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
! SID Length ! SID Value ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
o SID Length (1 octet) -- A natural number defining the number of
bits to be used in the SID field of the counter mode transform
nonce.
o SID Value (variable) -- The Sender ID value allocated to the group
member.
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5.3.3.1. GCKS Semantics
The GCKS maintains a SID counter (SIDC). It is incremented each time
a SENDER_ID attribute is distributed to a group member. The first
group member to register is given the SID of 1.
Any group member registering will be given a new SID value, which
allows group members to act as a group sender when an older SID value
becomes unusable (as described in the next section).
A GCKS MAY allocate multiple SID values in one SA SSA payload.
Allocating several SID values at the same time to a group member
expected to send at a high rate would obviate the need for the group
member to re-register as frequently.
If a GCKS allocates all SID values, it can no longer respond to GDOI
registrations and must re-initialize the entire group. This is done
by issuing DELETE notifications for all ESP and AH SAs in a GDOI
rekey message, resetting the SIDC to zero, and creating new ESP and
AH SAs that match the group policy. When group members re-register,
the SIDs are allocated again beginning with the value 1 as described
above. Each re-registering group member will be given a new SID and
the new group policy.
The SENDER_ID attribute MUST NOT be sent as part of a GROUPKEY-PUSH
message, because distributing the same sender-specific policy to more
than one group member may reduce the security of the group.
5.3.3.2. Group Member Semantics
The SENDER_ID attribute value distributed to the group member MUST be
used by that group member as the Sender Identifier (SID) field
portion of the IV. The SID is used for all counter mode SAs
distributed by the GCKS to be used for communications sent as a part
of this group.
When the Sender-Specific IV (SSIV) field for any IPsec SA is
exhausted, the group member MUST no longer act as a sender using its
active SID. The group member SHOULD re-register, during which time
the GCKS will issue a new SID to the group member. The new SID
replaces the existing SID used by this group member, and also resets
the SSIV value to it's starting value. A group member MAY re-
register prior to the actual exhaustion of the SSIV field to avoid
dropping data packets due to the exhaustion of available SSIV values
combined with a particular SID value.
A group member MUST NOT process SENDER_ID attribute present in a
GROUPKEY-PUSH message.
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6. IANA Considerations
The GDOI KEK Attribute named SIG_HASH_ALGORITHM [GDOI-REG] should be
assigned a new Algorithm Type value from the RESERVED space to
represent the SHA-256 hash algorithm as defined. The new algorithm
name should be SIG_HASH_SHA256.
A new GDOI SA TEK type Protocol-ID type [GDOI-REG] should be assigned
from the RESERVED space. The new algorithm id should be called
GDOI_PROTO_IPSEC_AH, and refers to the IPsec AH encapsulation.
A new Next Payload Type [ISAKMP-REG] should be assigned. The new
type is called "SA Group Associated Policy (GAP)".
A new namespace should be created in the GDOI Payloads registry
[GDOI-REG] to describe SA SSA Payload Values. The following rules
apply to define the attributes in SA SSA Payload Values:
Attribute Type Value Type
---- ----- ----
RESERVED 0
ACTIVATION_TIME_DELAY 1 B
DEACTIVATION_TIME_DELAY 2 B
SENDER_ID 3 V
Reserved to IANA 2-127
Private Use 128-255
A new IPSEC Security Association Attribute [ISAKMP-REG] defining the
preservation of IP addresses is needed. The attribute class is
called "Address Preservation", and it is a Basic type. The following
rules apply to define the values of the attribute:
Name Value
---- -----
Reserved 0
None 1
Source-Only 2
Destination-Only 3
Source-And-Destination 4
Reserved to IANA 5-61439
Private Use 61440-65535
A new IPSEC Security Association Attribute [ISAKMP-REG] defining the
SA direction is needed. The attribute class is called "SA
Direction", and it is a Basic type. The following rules apply to
define the values of the attribute:
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Name Value
---- -----
Reserved 0
Sender-Only 1
Receiver-Only 2
Symmetric 3
Reserved to IANA 4-61439
Private Use 61440-65535
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7. Security Considerations
This memo describes additional clarification and adds additional
attributes to be passed within the GDOI protocol. The security
considerations in RFC 3547 remain accurate, with the following
additions.
o Several minor cryptographic hash algorithm agility issues are
resolved, and the stronger SHA-256 cryptographic hash algorithm is
added.
o Protocol analysis has revealed a man-in-the-middle attack when the
GCKS does not authorize group members based on their IKE
authentication credentials. This is true even when a CERT and POP
payloads are used for authorization. Although suggested as an
option in RFC 3547, a GDOI device (group member or GCKS) SHOULD
NOT accept an identity in a CERT payload that does not match the
IKE identity used to authenticate the group member.
o Any SA TEK specifying a counter-based mode of operation with
multiple senders MUST construct the IVs in each SA TEK according
to [I-D.ietf-msec-ipsec-group-counter-modes]. The SID MUST either
be pre-configured on all group members or distributed using the
SENDER_ID attribute in the SA GAP payload. However, use of the
SENDER_ID attribute is RECOMMENDED.
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8. Acknowledgements
The authors are grateful to Catherine Meadows for her careful review
and suggestions for mitigating the man-in-the-middle attack she had
previously identified.
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9. References
9.1. Normative References
[I-D.ietf-msec-ipsec-group-counter-modes]
McGrew, D. and B. Weis, "Using Counter Modes with
Encapsulating Security Payload (ESP) and Authentication
Header (AH) to Protect Group Traffic",
draft-ietf-msec-ipsec-group-counter-modes-03 (work in
progress), March 2009.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3547] Baugher, M., Weis, B., Hardjono, T., and H. Harney, "The
Group Domain of Interpretation", RFC 3547, July 2003.
[RFC5374] Weis, B., Gross, G., and D. Ignjatic, "Multicast
Extensions to the Security Architecture for the Internet
Protocol", RFC 5374, November 2008.
9.2. Informative References
[FIPS.180-2.2002]
National Institute of Standards and Technology, "Secure
Hash Standard", FIPS PUB 180-2, August 2002, <http://
csrc.nist.gov/publications/fips/fips180-2/fips180-2.pdf>.
[GDOI-REG]
Internet Assigned Numbers Authority, "Group Domain of
Interpretation (GDOI) Payload Type Values", IANA Registry,
December 2004,
<http://www.iana.org/assignments/gdoi-payloads>.
[ISAKMP-REG]
Internet Assigned Numbers Authority, "Internet Security
Association and Key Management Protocol (ISAKMP)
Identifiers ISAKMP Attributes", IANA Registry,
January 2006,
<http://www.iana.org/assignments/isakmp-registry>.
[MP04] Meadows, C. and D. Pavlovic, "Deriving, Attacking, and
Defending the GDOI Protocol", ESORICS 2004 pp. 53-72,
September 2004.
[RFC2407] Piper, D., "The Internet IP Security Domain of
Interpretation for ISAKMP", RFC 2407, November 1998.
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[RFC2408] Maughan, D., Schneider, M., and M. Schertler, "Internet
Security Association and Key Management Protocol
(ISAKMP)", RFC 2408, November 1998.
[RFC3447] Jonsson, J. and B. Kaliski, "Public-Key Cryptography
Standards (PKCS) #1: RSA Cryptography Specifications
Version 2.1", RFC 3447, February 2003.
[RFC3686] Housley, R., "Using Advanced Encryption Standard (AES)
Counter Mode With IPsec Encapsulating Security Payload
(ESP)", RFC 3686, January 2004.
[RFC4046] Baugher, M., Canetti, R., Dondeti, L., and F. Lindholm,
"Multicast Security (MSEC) Group Key Management
Architecture", RFC 4046, April 2005.
[RFC4106] Viega, J. and D. McGrew, "The Use of Galois/Counter Mode
(GCM) in IPsec Encapsulating Security Payload (ESP)",
RFC 4106, June 2005.
[RFC4302] Kent, S., "IP Authentication Header", RFC 4302,
December 2005.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, December 2005.
[RFC4309] Housley, R., "Using Advanced Encryption Standard (AES) CCM
Mode with IPsec Encapsulating Security Payload (ESP)",
RFC 4309, December 2005.
[RFC4543] McGrew, D. and J. Viega, "The Use of Galois Message
Authentication Code (GMAC) in IPsec ESP and AH", RFC 4543,
May 2006.
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Authors' Addresses
Brian Weis
Cisco Systems
170 W. Tasman Drive
San Jose, California 95134-1706
USA
Phone: +1-408-526-4796
Email: bew@cisco.com
Sheela Rowles
Cisco Systems
170 W. Tasman Drive
San Jose, California 95134-1706
USA
Phone: +1-408-527-7677
Email: sheela@cisco.com
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