< draft-ietf-kitten-pkinit-alg-agility-03.txt   draft-ietf-kitten-pkinit-alg-agility-04.txt >
Kitten Working Group L. Hornquist Astrand Kitten Working Group L. Hornquist Astrand
Internet-Draft Apple, Inc Internet-Draft Apple, Inc
Updates: 4556 (if approved) L. Zhu Updates: 4556 (if approved) L. Zhu
Intended status: Standards Track Microsoft Corporation Intended status: Standards Track Microsoft Corporation
Expires: May 9, 2019 M. Wasserman Expires: August 7, 2019 M. Wasserman
Painless Security Painless Security
G. Hudson, Ed. G. Hudson, Ed.
MIT MIT
November 5, 2018 February 3, 2019
PKINIT Algorithm Agility PKINIT Algorithm Agility
draft-ietf-kitten-pkinit-alg-agility-03 draft-ietf-kitten-pkinit-alg-agility-04
Abstract Abstract
This document updates PKINIT, as defined in RFC 4556, to remove This document updates PKINIT, as defined in RFC 4556, to remove
protocol structures tied to specific cryptographic algorithms. The protocol structures tied to specific cryptographic algorithms. The
PKINIT key derivation function is made negotiable, the digest PKINIT key derivation function is made negotiable, and the digest
algorithms for signing the pre-authentication data and the client's algorithms for signing the pre-authentication data and the client's
X.509 certificates are made discoverable. X.509 certificates are made discoverable.
These changes provide preemptive protection against vulnerabilities These changes provide preemptive protection against vulnerabilities
discovered in the future against any specific cryptographic discovered in the future against any specific cryptographic
algorithm, and allow incremental deployment of newer algorithms. algorithm, and allow incremental deployment of newer algorithms.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on May 9, 2019. This Internet-Draft will expire on August 7, 2019.
Copyright Notice Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
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carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
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2. Requirements Notation . . . . . . . . . . . . . . . . . . . . 4 2. Requirements Notation . . . . . . . . . . . . . . . . . . . . 4
3. paChecksum Agility . . . . . . . . . . . . . . . . . . . . . 4 3. paChecksum Agility . . . . . . . . . . . . . . . . . . . . . 4
4. CMS Digest Algorithm Agility . . . . . . . . . . . . . . . . 4 4. CMS Digest Algorithm Agility . . . . . . . . . . . . . . . . 4
5. X.509 Certificate Signer Algorithm Agility . . . . . . . . . 5 5. X.509 Certificate Signer Algorithm Agility . . . . . . . . . 5
6. KDF agility . . . . . . . . . . . . . . . . . . . . . . . . . 6 6. KDF agility . . . . . . . . . . . . . . . . . . . . . . . . . 6
7. Test vectors . . . . . . . . . . . . . . . . . . . . . . . . 11 7. Test vectors . . . . . . . . . . . . . . . . . . . . . . . . 11
7.1. Common Inputs . . . . . . . . . . . . . . . . . . . . . . 11 7.1. Common Inputs . . . . . . . . . . . . . . . . . . . . . . 11
7.2. Test Vector for SHA-1, enctype 18 . . . . . . . . . . . . 12 7.2. Test Vector for SHA-1, enctype 18 . . . . . . . . . . . . 12
7.2.1. Specific Inputs . . . . . . . . . . . . . . . . . . . 12 7.2.1. Specific Inputs . . . . . . . . . . . . . . . . . . . 12
7.2.2. Outputs . . . . . . . . . . . . . . . . . . . . . . . 12 7.2.2. Outputs . . . . . . . . . . . . . . . . . . . . . . . 12
7.3. Test Vector for SHA-256, enctype . . . . . . . . . . . . 12 7.3. Test Vector for SHA-256, enctype . . . . . . . . . . . . 13
7.3.1. Specific Inputs . . . . . . . . . . . . . . . . . . . 12 7.3.1. Specific Inputs . . . . . . . . . . . . . . . . . . . 13
7.3.2. Outputs . . . . . . . . . . . . . . . . . . . . . . . 12 7.3.2. Outputs . . . . . . . . . . . . . . . . . . . . . . . 13
7.4. Test Vector for SHA-512, enctype . . . . . . . . . . . . 12 7.4. Test Vector for SHA-512, enctype . . . . . . . . . . . . 13
7.4.1. Specific Inputs . . . . . . . . . . . . . . . . . . . 12 7.4.1. Specific Inputs . . . . . . . . . . . . . . . . . . . 13
7.4.2. Outputs . . . . . . . . . . . . . . . . . . . . . . . 13 7.4.2. Outputs . . . . . . . . . . . . . . . . . . . . . . . 13
8. Security Considerations . . . . . . . . . . . . . . . . . . . 13 8. Security Considerations . . . . . . . . . . . . . . . . . . . 13
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 13 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
11.1. Normative References . . . . . . . . . . . . . . . . . . 13 11.1. Normative References . . . . . . . . . . . . . . . . . . 14
11.2. Informative References . . . . . . . . . . . . . . . . . 15 11.2. Informative References . . . . . . . . . . . . . . . . . 15
Appendix A. PKINIT ASN.1 Module . . . . . . . . . . . . . . . . 15 Appendix A. PKINIT ASN.1 Module . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
1. Introduction 1. Introduction
This document updates PKINIT [RFC4556] to remove protocol structures This document updates PKINIT [RFC4556] to remove protocol structures
tied to specific cryptographic algorithms. The PKINIT key derivation tied to specific cryptographic algorithms. The PKINIT key derivation
function is made negotiable, the digest algorithms for signing the function is made negotiable, the digest algorithms for signing the
pre-authentication data and the client's X.509 certificates are made pre-authentication data and the client's X.509 certificates are made
discoverable. discoverable.
These changes provide preemptive protection against vulnerabilities These changes provide preemptive protection against vulnerabilities
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attacks on later hash function designs in the MD4, MD5 [RFC1321] and attacks on later hash function designs in the MD4, MD5 [RFC1321] and
SHA [RFC6234] family. These attacks and their consequences are SHA [RFC6234] family. These attacks and their consequences are
discussed in [RFC6194]. These discoveries challenged the security of discussed in [RFC6194]. These discoveries challenged the security of
protocols relying on the collision resistance properties of these protocols relying on the collision resistance properties of these
hashes. hashes.
The Internet Engineering Task Force (IETF) called for actions to The Internet Engineering Task Force (IETF) called for actions to
update existing protocols to provide crypto algorithm agility so that update existing protocols to provide crypto algorithm agility so that
protocols support multiple cryptographic algorithms (including hash protocols support multiple cryptographic algorithms (including hash
functions) and provide clean, tested transition strategies between functions) and provide clean, tested transition strategies between
algorithms. algorithms, as recommended by BCP 201 [RFC7696].
This document updates PKINIT to provide crypto algorithm agility. This document updates PKINIT to provide crypto algorithm agility.
Several protocol structures used in the [RFC4556] protocol are either Several protocol structures used in the [RFC4556] protocol are either
tied to SHA-1, or do not support negotiation or discovery, but are tied to SHA-1, or do not support negotiation or discovery, but are
instead based on local policy. The following concerns have been instead based on local policy. The following concerns have been
addressed in this update: addressed in this update:
o The checksum algorithm in the authentication request is hardwired o The checksum algorithm in the authentication request is hardwired
to use SHA-1 [RFC6234]. to use SHA-1 [RFC6234].
o The acceptable digest algorithms for signing the authentication o The acceptable digest algorithms for signing the authentication
data are not discoverable. data are not discoverable.
o The key derivation function in Section 3.2.3 of [RFC4556] is o The key derivation function in Section 3.2.3.1 of [RFC4556] is
hardwired to use SHA-1. hardwired to use SHA-1.
o The acceptable digest algorithms for signing the client X.509 o The acceptable digest algorithms for signing the client X.509
certificates are not discoverable. certificates are not discoverable.
To address these concerns, new key derivation functions (KDFs), To address these concerns, new key derivation functions (KDFs),
identified by object identifiers, are defined. The PKINIT client identified by object identifiers, are defined. The PKINIT client
provides a list of KDFs in the request and the Key Distribution provides a list of KDFs in the request and the Key Distribution
Center (KDC) picks one in the response, thus a mutually-supported KDF Center (KDC) picks one in the response, thus a mutually-supported KDF
is negotiated. is negotiated.
Furthermore, structures are defined to allow the client to discover Furthermore, structures are defined to allow the client to discover
the Cryptographic Message Syntax (CMS) [RFC5652] digest algorithms the Cryptographic Message Syntax (CMS) [RFC5652] digest algorithms
supported by the KDC for signing the pre-authentication data and supported by the KDC for signing the pre-authentication data and
signing the client X.509 certificate. signing the client X.509 certificate.
2. Requirements Notation 2. Requirements Notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
document are to be interpreted as described in [RFC2119]. "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. paChecksum Agility 3. paChecksum Agility
The paChecksum defined in Section 3.2.1 of [RFC4556] provides a The paChecksum defined in Section 3.2.1 of [RFC4556] provides a
cryptographic binding between the client's pre-authentication data cryptographic binding between the client's pre-authentication data
and the corresponding Kerberos request body. This also prevents the and the corresponding Kerberos request body. This also prevents the
KDC body from being tampered with. SHA-1 is the only allowed KDC-REQ body from being tampered with. SHA-1 is the only allowed
checksum algorithm defined in [RFC4556]. This facility relies on the checksum algorithm defined in [RFC4556]. This facility relies on the
collision resistance properties of the SHA-1 checksum [RFC6234]. collision resistance properties of the SHA-1 checksum [RFC6234].
When the reply key delivery mechanism is based on public key When the reply key delivery mechanism is based on public key
encryption as described in Section 3.2.3. of [RFC4556], the encryption as described in Section 3.2.3.2 of [RFC4556], the
asChecksum in the KDC reply provides the binding between the pre- asChecksum in the KDC reply provides the binding between the pre-
authentication and the ticket request and response messages, and authentication and the ticket request and response messages, and
integrity protection for the unauthenticated clear text in these integrity protection for the unauthenticated clear text in these
messages. However, if the reply key delivery mechanism is based on messages. However, if the reply key delivery mechanism is based on
the Diffie-Hellman key agreement as described in Section 3.2.3.1 of the Diffie-Hellman key agreement as described in Section 3.2.3.1 of
[RFC4556], the security provided by using SHA-1 in the paChecksum is [RFC4556], the security provided by using SHA-1 in the paChecksum is
weak. In this case, the new KDF selected by the KDC as described in weak, and nothing else cryptographically binds the AS request to the
Section 6 provides the cryptographic binding and integrity ticket response. In this case, the new KDF selected by the KDC as
protection. described in Section 6 provides the cryptographic binding and
integrity protection.
4. CMS Digest Algorithm Agility 4. CMS Digest Algorithm Agility
When the KDC_ERR_DIGEST_IN_SIGNED_DATA_NOT_ACCEPTED error is returned When the KDC_ERR_DIGEST_IN_SIGNED_DATA_NOT_ACCEPTED error is returned
as described In section 3.2.2 of [RFC4556], implementations as described in Section 3.2.2 of [RFC4556], implementations
comforming to this specification can OPTIONALLY send back a list of conforming to this specification can OPTIONALLY send back a list of
supported CMS types signifying the digest algorithms supported by the supported CMS types signifying the digest algorithms supported by the
KDC, in the decreasing preference order. This is accomplished by KDC, in the decreasing preference order. This is accomplished by
including a TD_CMS_DATA_DIGEST_ALGORITHMS typed data element in the including a TD_CMS_DATA_DIGEST_ALGORITHMS typed data element in the
error data. error data.
td-cms-digest-algorithms INTEGER ::= 111 td-cms-digest-algorithms INTEGER ::= 111
The corresponding data for the TD_CMS_DATA_DIGEST_ALGORITHMS contains The corresponding data for the TD_CMS_DATA_DIGEST_ALGORITHMS contains
the ASN.1 Distinguished Encoding Rules (DER) [X680] [X690] encoded the ASN.1 Distinguished Encoding Rules (DER) [X680] [X690] encoded
TD-CMS-DIGEST-ALGORITHMS-DATA structure defined as follows: TD-CMS-DIGEST-ALGORITHMS-DATA structure defined as follows:
TD-CMS-DIGEST-ALGORITHMS-DATA ::= SEQUENCE OF TD-CMS-DIGEST-ALGORITHMS-DATA ::= SEQUENCE OF
AlgorithmIdentifier AlgorithmIdentifier
-- Contains the list of CMS algorithm [RFC5652] -- Contains the list of CMS algorithm [RFC5652]
-- identifiers that identify the digest algorithms -- identifiers that indicate the digest algorithms
-- acceptable by the KDC for signing CMS data in -- acceptable by the KDC for signing CMS data in
-- the order of decreasing preference. -- the order of decreasing preference.
The algorithm identifiers in the TD-CMS-DIGEST-ALGORITHMS identifiy The algorithm identifiers in the TD-CMS-DIGEST-ALGORITHMS identifiy
digest algorithms supported by the KDC. digest algorithms supported by the KDC.
This information sent by the KDC via TD_CMS_DATA_DIGEST_ALGORITHMS This information sent by the KDC via TD_CMS_DATA_DIGEST_ALGORITHMS
can facilitate trouble-shooting when none of the digest algorithms can facilitate trouble-shooting when none of the digest algorithms
supported by the client is supported by the KDC. supported by the client is supported by the KDC.
5. X.509 Certificate Signer Algorithm Agility 5. X.509 Certificate Signer Algorithm Agility
When the client's X.509 certificate is rejected and the When the client's X.509 certificate is rejected and the
KDC_ERR_DIGEST_IN_SIGNED_DATA_NOT_ACCEPTED error is returned as KDC_ERR_DIGEST_IN_SIGNED_DATA_NOT_ACCEPTED error is returned as
described in section 3.2.2 of [RFC4556], conforming implementations described in Section 3.2.2 of [RFC4556], implementations conforming
can OPTIONALLY send a list of digest algorithms acceptable by the KDC to this specification can OPTIONALLY send a list of digest algorithms
for use by the Certificate Authority (CA) in signing the client's acceptable by the KDC for use by the Certificate Authority (CA) in
X.509 certificate, in the decreasing preference order. This is signing the client's X.509 certificate, in the decreasing preference
accomplished by including a TD_CERT_DIGEST_ALGORITHMS typed data order. This is accomplished by including a TD_CERT_DIGEST_ALGORITHMS
element in the error data. The corresponding data contains the ASN.1 typed data element in the error data. The corresponding data
DER encoding of the structure TD-CERT-DIGEST-ALGORITHMS-DATA defined contains the ASN.1 DER encoding of the structure TD-CERT-DIGEST-
as follows: ALGORITHMS-DATA defined as follows:
td-cert-digest-algorithms INTEGER ::= 112 td-cert-digest-algorithms INTEGER ::= 112
TD-CERT-DIGEST-ALGORITHMS-DATA ::= SEQUENCE { TD-CERT-DIGEST-ALGORITHMS-DATA ::= SEQUENCE {
allowedAlgorithms [0] SEQUENCE OF AlgorithmIdentifier, allowedAlgorithms [0] SEQUENCE OF AlgorithmIdentifier,
-- Contains the list of CMS algorithm [RFC5652] -- Contains the list of CMS algorithm [RFC5652]
-- identifiers that identify the digest algorithms -- identifiers that identify the digest algorithms
-- that are used by the CA to sign the client's -- that are used by the CA to sign the client's
-- X.509 certificate and acceptable by the KDC in -- X.509 certificate and acceptable by the KDC in
-- the process of validating the client's X.509 -- the process of validating the client's X.509
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X.509 certificate that has been rejected by the KDC in the process of X.509 certificate that has been rejected by the KDC in the process of
validating the client's certificate [RFC5280]. validating the client's certificate [RFC5280].
6. KDF agility 6. KDF agility
Based on [RFC3766] and [X9.42], Section 3.2.3.1 of [RFC4556] defines Based on [RFC3766] and [X9.42], Section 3.2.3.1 of [RFC4556] defines
a Key Derivation Function (KDF) that derives a Kerberos protocol key a Key Derivation Function (KDF) that derives a Kerberos protocol key
based on the secret value generated by the Diffie-Hellman key based on the secret value generated by the Diffie-Hellman key
exchange. This KDF requires the use of SHA-1 [RFC6234]. exchange. This KDF requires the use of SHA-1 [RFC6234].
New KDFs defined in this document based on [SP80056A] can be used in The KDF algorithm described in this document (based on [SP80056A])
conjunction with any hash functions. can be implemented using any cryptographic hash function.
A new KDF is identified by an object identifier. The following KDF A new KDF for PKINIT usage is identified by an object identifier.
object identifiers are defined: The following KDF object identifiers are defined:
id-pkinit OBJECT IDENTIFIER ::= id-pkinit OBJECT IDENTIFIER ::=
{ iso(1) identified-organization(3) dod(6) internet(1) { iso(1) identified-organization(3) dod(6) internet(1)
security(5) kerberosv5(2) pkinit (3) } security(5) kerberosv5(2) pkinit (3) }
-- Defined in RFC 4556 and quoted here for the reader. -- Defined in RFC 4556 and quoted here for the reader.
id-pkinit-kdf OBJECT IDENTIFIER ::= { id-pkinit kdf(6) } id-pkinit-kdf OBJECT IDENTIFIER ::= { id-pkinit kdf(6) }
-- PKINIT KDFs -- PKINIT KDFs
id-pkinit-kdf-ah-sha1 OBJECT IDENTIFIER id-pkinit-kdf-ah-sha1 OBJECT IDENTIFIER
::= { id-pkinit-kdf sha1(1) } ::= { id-pkinit-kdf sha1(1) }
-- SP800-56A ASN.1 structured hash based KDF using SHA-1 -- SP800-56A ASN.1 structured hash-based KDF using SHA-1
id-pkinit-kdf-ah-sha256 OBJECT IDENTIFIER id-pkinit-kdf-ah-sha256 OBJECT IDENTIFIER
::= { id-pkinit-kdf sha256(2) } ::= { id-pkinit-kdf sha256(2) }
-- SP800-56A ASN.1 structured hash based KDF using SHA-256 -- SP800-56A ASN.1 structured hash-based KDF using SHA-256
id-pkinit-kdf-ah-sha512 OBJECT IDENTIFIER id-pkinit-kdf-ah-sha512 OBJECT IDENTIFIER
::= { id-pkinit-kdf sha512(3) } ::= { id-pkinit-kdf sha512(3) }
-- SP800-56A ASN.1 structured hash based KDF using SHA-512 -- SP800-56A ASN.1 structured hash-based KDF using SHA-512
id-pkinit-kdf-ah-sha384 OBJECT IDENTIFIER id-pkinit-kdf-ah-sha384 OBJECT IDENTIFIER
::= { id-pkinit-kdf sha384(4) } ::= { id-pkinit-kdf sha384(4) }
-- SP800-56A ASN.1 structured hash based KDF using SHA-384 -- SP800-56A ASN.1 structured hash-based KDF using SHA-384
Where id-pkinit is defined in [RFC4556]. The id-pkinit-kdf-ah-sha1 Where id-pkinit is defined in [RFC4556]. All key derivation
KDF is the ASN.1 structured hash based KDF (HKDF) [SP80056A] that functions specified above use the one-step key derivation method
uses SHA-1 [RFC6234] as the hash function. Similarly id-pkinit-kdf- described in Section 5.8.2.1 of [SP80056A], using the ASN.1 format
ah-sha256 and id-pkinit-kdf-ah-sha512 are the ASN.1 structured HKDF for FixedInfo, and Section 4.1 of [SP80056C], using option 1 for the
using SHA-256 [RFC6234] and SHA-512 [RFC6234] respectively. auxiliary function H. id-pkinit-kdf-ah-sha1 uses SHA-1 [RFC6234] as
the hash function. id-pkinit-kdf-ah-sha256, id-pkinit-kdf-ah-sha356,
and id-pkinit-kdf-ah-sha512 use SHA-256 [RFC6234], SHA-384 ([RFC6234]
and SHA-512 [RFC6234] respectively.
To name the input parameters, an abbreviated version of the ASN.1 To name the input parameters, an abbreviated version of the key
version of the KDF from [SP80056A] is described below, use [SP80056A] derivation method is described below.
for the full reference.
1. reps = ceiling (keydatalen/hash length (H)) 1. reps = ceiling(L/H_outputBits)
2. Initialize a 32-bit, big-endian bit string counter as 1. 2. Initialize a 32-bit, big-endian bit string counter as 1.
3. For i = 1 to reps by 1, do the following: 3. For i = 1 to reps by 1, do the following:
1. Compute Hashi = H(counter || Z || OtherInfo). 1. Compute Hashi = H(counter || Z || OtherInfo).
2. Increment counter (modulo 2^32) 2. Increment counter (not to exceed 2^32-1)
4. Set key_material = Hash1 || Hash2 || ... so that length of key is 4. Set key_material = Hash1 || Hash2 || ... so that the length of
K bits. key_material is L bits, truncating the last block as necessary.
5. The above ASN.1 structured [SP80056A] HKDF produces a bit string 5. The above KDF produces a bit string of length L in bits as the
of length K in bits as the keying material, and then the AS reply keying material. The AS reply key is the output of random-to-
key is the output of random-to-key() [RFC3961] using that key() [RFC3961] using that keying material as the input.
returned keying material as the input.
The input parameters for these KDFs are provided as follows: The input parameters for these KDFs are provided as follows:
o The key data length (K) is the key-generation seed length in bits o H_outputBits is 160 bits for id-pkinit-kdf-ah-sha1, 256 bits for
[RFC3961] for the Authentication Service (AS) reply key. The id-pkinit-kdf-ah-sha256, 384 bits for id-pkinit-kdf-ah-sha384, and
enctype of the AS reply key is selected according to [RFC4120]. 512 bits for id-pkinit-kdf-ah-sha512.
o The hash length (H) is 160 bits for id-pkinit-kdf-ah-sha1, 256 o max_H_inputBits is 2^64.
bits for id-pkinit-kdf-ah-sha256, 384 bits for id-pkinit-kdf-ah-
sha384 and 512 bits for id-pkinit-kdf-ah-sha512.
o The secret value (Z) is the shared secret value generated by the o The secret value (Z) is the shared secret value generated by the
Diffie-Hellman exchange. The Diffie-Hellman shared value is first Diffie-Hellman exchange. The Diffie-Hellman shared value is first
padded with leading zeros such that the size of the secret value padded with leading zeros such that the size of the secret value
in octets is the same as that of the modulus, then represented as in octets is the same as that of the modulus, then represented as
a string of octets in big-endian order. a string of octets in big-endian order.
o The key data length (L) is the key-generation seed length in bits
[RFC3961] for the Authentication Service (AS) reply key. The
enctype of the AS reply key is selected according to [RFC4120].
o The algorithm identifier (algorithmID) input parameter is the o The algorithm identifier (algorithmID) input parameter is the
identifier of the respective KDF. For example, this is id-pkinit- identifier of the respective KDF. For example, this is id-pkinit-
kdf-ah-sha1 if the KDF is the [SP80056A] ASN.1 structured HKDF kdf-ah-sha1 if the KDF uses SHA-1 as the hash.
using SHA-1 as the hash.
o The initiator identifier (partyUInfo) contains the ASN.1 DER o The initiator identifier (partyUInfo) contains the ASN.1 DER
encoding of the KRB5PrincipalName [RFC4556] that identifies the encoding of the KRB5PrincipalName [RFC4556] that identifies the
client as specified in the AS-REQ [RFC4120] in the request. client as specified in the AS-REQ [RFC4120] in the request.
o The recipient identifier (partyVInfo) contains the ASN.1 DER o The recipient identifier (partyVInfo) contains the ASN.1 DER
encoding of the KRB5PrincipalName [RFC4556] that identifies the encoding of the KRB5PrincipalName [RFC4556] that identifies the
TGS as specified in the AS-REQ [RFC4120] in the request. TGS as specified in the AS-REQ [RFC4120] in the request.
o The supplemental public information (suppPubInfo) is the ASN.1 DER o The supplemental public information (suppPubInfo) is the ASN.1 DER
encoding of the structure PkinitSuppPubInfo as defined later in encoding of the structure PkinitSuppPubInfo as defined later in
this section. this section.
o The supplemental private information (suppPrivInfo) is absent. o The supplemental private information (suppPrivInfo) is absent.
o The maximum hash input length is 2^64 in bits. OtherInfo is the ASN.1 DER encoding of the following sequence:
The structure for OtherInfo is defined as follows:
OtherInfo ::= SEQUENCE { OtherInfo ::= SEQUENCE {
algorithmID AlgorithmIdentifier, algorithmID AlgorithmIdentifier,
partyUInfo [0] OCTET STRING, partyUInfo [0] OCTET STRING,
partyVInfo [1] OCTET STRING, partyVInfo [1] OCTET STRING,
suppPubInfo [2] OCTET STRING OPTIONAL, suppPubInfo [2] OCTET STRING OPTIONAL,
suppPrivInfo [3] OCTET STRING OPTIONAL suppPrivInfo [3] OCTET STRING OPTIONAL
} }
The structure PkinitSuppPubInfo is defined as follows: The structure PkinitSuppPubInfo is defined as follows:
PkinitSuppPubInfo ::= SEQUENCE { PkinitSuppPubInfo ::= SEQUENCE {
enctype [0] Int32, enctype [0] Int32,
-- The enctype of the AS reply key -- The enctype of the AS reply key.
as-REQ [1] OCTET STRING, as-REQ [1] OCTET STRING,
-- This contains the AS-REQ in the request. -- The DER encoding of the AS-REQ [RFC4120] from the
-- client.
pk-as-rep [2] OCTET STRING, pk-as-rep [2] OCTET STRING,
-- Contains the DER encoding of the type -- The DER encoding of the PA-PK-AS-REP [RFC4556] in the
-- PA-PK-AS-REP [RFC4556] in the KDC reply. -- KDC reply.
... ...
} }
The PkinitSuppPubInfo structure contains mutually-known public The PkinitSuppPubInfo structure contains mutually-known public
information specific to the authentication exchange. The enctype information specific to the authentication exchange. The enctype
field is the enctype of the AS reply key as selected according to field is the enctype of the AS reply key as selected according to
[RFC4120]. The as-REQ field contains the DER encoding of the type [RFC4120]. The as-REQ field contains the DER encoding of the type
AS-REQ [RFC4120] in the request sent from the client to the KDC. AS-REQ [RFC4120] in the request sent from the client to the KDC.
Note that the as-REQ field does not include the wrapping 4 octet Note that the as-REQ field does not include the wrapping 4 octet
length field when TCP is used. The pk-as-rep field contains the DER length field when TCP is used. The pk-as-rep field contains the DER
skipping to change at page 10, line 50 skipping to change at page 11, line 6
} }
The new field kdf in the extended DHRepInfo structure identifies the The new field kdf in the extended DHRepInfo structure identifies the
KDF picked by the KDC. This kdf field MUST be filled by the KDF picked by the KDC. This kdf field MUST be filled by the
comforming KDC if the supportedKDFs field is present in the request, comforming KDC if the supportedKDFs field is present in the request,
and it MUST be one of the KDFs supported by the client as indicated and it MUST be one of the KDFs supported by the client as indicated
in the request. Which KDF is chosen is a matter of the local policy in the request. Which KDF is chosen is a matter of the local policy
on the KDC. on the KDC.
If the supportedKDFs field is not present in the request, the kdf If the supportedKDFs field is not present in the request, the kdf
field in the reply MUST be absent. field in the reply MUST be absent, and the key derivation function
from Section 3.2.3.1 of [RFC4556] MUST be used.
If the client fills the supportedKDFs field in the request, but the If the client fills the supportedKDFs field in the request, but the
kdf field in the reply is not present, the client can deduce that the kdf field in the reply is not present, the client can deduce that the
KDC is not updated to conform with this specification. In that case, KDC is not updated to conform with this specification, or that the
it is a matter of local policy on the client whether to reject the exchange was subjected to a downgrade attack. It is a matter of
reply when the kdf field is absent in the reply. local policy on the client whether to reject the reply when the kdf
field is absent in the reply; if compatibility with non-updated KDCs
is not a concern, the reply should be rejected.
Implementations comforming to this specification MUST support id- Implementations comforming to this specification MUST support id-
pkinit-kdf-ah-sha256. pkinit-kdf-ah-sha256.
This document introduces the following new PKINIT error code: This document introduces the following new PKINIT error code:
o KDC_ERR_NO_ACCEPTABLE_KDF 100 o KDC_ERR_NO_ACCEPTABLE_KDF 100
If no acceptable KDF is found, the error KDC_ERR_NO_ACCEPTABLE_KDF If no acceptable KDF is found, the error KDC_ERR_NO_ACCEPTABLE_KDF
(100) will be returned.. (100) will be returned..
skipping to change at page 13, line 20 skipping to change at page 13, line 43
key-material: Length = 24 bytes, Hex Representation = key-material: Length = 24 bytes, Hex Representation =
D3C78A79 D65213EF E9A826F7 5DFB01F7 2362FB16 FB01DAD6 D3C78A79 D65213EF E9A826F7 5DFB01F7 2362FB16 FB01DAD6
key: Length = 32 bytes, Hex Representation = key: Length = 32 bytes, Hex Representation =
D3C78A79 D65213EF E9A826F7 5DFB01F7 2362FB16 FB01DAD6 D3C78A79 D65213EF E9A826F7 5DFB01F7 2362FB16 FB01DAD6
8. Security Considerations 8. Security Considerations
This document describes negotiation of checksum types, key derivation This document describes negotiation of checksum types, key derivation
functions and other cryptographic functions. If negotiation is done functions and other cryptographic functions. If a given negotiation
unauthenticated, care MUST be taken to accept only acceptable values. is unauthenticated, care must be taken to accept only secure values;
to do otherwise allows an active attacker to perform a downgrade
attack.
9. Acknowledgements 9. Acknowledgements
Jeffery Hutzelman, Shawn Emery, Tim Polk and Kelley Burgin reviewed Jeffery Hutzelman, Shawn Emery, Tim Polk and Kelley Burgin reviewed
the document and provided suggestions for improvements. the document and provided suggestions for improvements.
10. IANA Considerations 10. IANA Considerations
IANA is requested to update the following registrations in the IANA is requested to update the following registrations in the
Kerberos Pre-authentication and Typed Data Registry created by Kerberos Pre-authentication and Typed Data Registry created by
skipping to change at page 14, line 34 skipping to change at page 15, line 14
[RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70, [RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
RFC 5652, DOI 10.17487/RFC5652, September 2009, RFC 5652, DOI 10.17487/RFC5652, September 2009,
<https://www.rfc-editor.org/info/rfc5652>. <https://www.rfc-editor.org/info/rfc5652>.
[RFC6234] Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms [RFC6234] Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms
(SHA and SHA-based HMAC and HKDF)", RFC 6234, (SHA and SHA-based HMAC and HKDF)", RFC 6234,
DOI 10.17487/RFC6234, May 2011, DOI 10.17487/RFC6234, May 2011,
<https://www.rfc-editor.org/info/rfc6234>. <https://www.rfc-editor.org/info/rfc6234>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[SP80056A] [SP80056A]
Barker, E., Don, D., and M. Smid, "Recommendation for Barker, E., Chen, L., Roginsky, A., Vassilev, A., and R.
Pair-Wise Key Establishment Schemes Using Discrete Davis, "Recommendation for Pair-Wise Key Establishment
Logarithm Cryptography", March 2006. Schemes Using Discrete Logarithm Cryptography", April
2018.
[SP80056C]
Barker, E., Chen, L., and R. Davis, "Recommendation for
Key-Derivation Methods in Key-Establishment Schemes",
April 2018.
[X680] ITU, "ITU-T Recommendation X.680 (2002) | ISO/IEC [X680] ITU, "ITU-T Recommendation X.680 (2002) | ISO/IEC
8824-1:2002, Information technology - Abstract Syntax 8824-1:2002, Information technology - Abstract Syntax
Notation One (ASN.1): Specification of basic notation", Notation One (ASN.1): Specification of basic notation",
November 2008. November 2008.
[X690] ITU, "ITU-T Recommendation X.690 (2002) | ISO/IEC [X690] ITU, "ITU-T Recommendation X.690 (2002) | ISO/IEC
8825-1:2002, Information technology - ASN.1 encoding 8825-1:2002, Information technology - ASN.1 encoding
Rules: Specification of Basic Encoding Rules (BER), Rules: Specification of Basic Encoding Rules (BER),
Canonical Encoding Rules (CER) and Distinguished Encoding Canonical Encoding Rules (CER) and Distinguished Encoding
skipping to change at page 15, line 25 skipping to change at page 16, line 14
[RFC6150] Turner, S. and L. Chen, "MD4 to Historic Status", [RFC6150] Turner, S. and L. Chen, "MD4 to Historic Status",
RFC 6150, DOI 10.17487/RFC6150, March 2011, RFC 6150, DOI 10.17487/RFC6150, March 2011,
<https://www.rfc-editor.org/info/rfc6150>. <https://www.rfc-editor.org/info/rfc6150>.
[RFC6194] Polk, T., Chen, L., Turner, S., and P. Hoffman, "Security [RFC6194] Polk, T., Chen, L., Turner, S., and P. Hoffman, "Security
Considerations for the SHA-0 and SHA-1 Message-Digest Considerations for the SHA-0 and SHA-1 Message-Digest
Algorithms", RFC 6194, DOI 10.17487/RFC6194, March 2011, Algorithms", RFC 6194, DOI 10.17487/RFC6194, March 2011,
<https://www.rfc-editor.org/info/rfc6194>. <https://www.rfc-editor.org/info/rfc6194>.
[RFC7696] Housley, R., "Guidelines for Cryptographic Algorithm
Agility and Selecting Mandatory-to-Implement Algorithms",
BCP 201, RFC 7696, DOI 10.17487/RFC7696, November 2015,
<https://www.rfc-editor.org/info/rfc7696>.
[WANG04] Wang, X., Lai, X., Fheg, D., Chen, H., and X. Yu, [WANG04] Wang, X., Lai, X., Fheg, D., Chen, H., and X. Yu,
"Cryptanalysis of Hash functions MD4 and RIPEMD", August "Cryptanalysis of Hash functions MD4 and RIPEMD", August
2004. 2004.
[X9.42] ANSI, "Public Key Cryptography for the Financial Services [X9.42] ANSI, "Public Key Cryptography for the Financial Services
Industry: Agreement of Symmetric Keys Using Discrete Industry: Agreement of Symmetric Keys Using Discrete
Logarithm Cryptography", 2003. Logarithm Cryptography", 2003.
Appendix A. PKINIT ASN.1 Module Appendix A. PKINIT ASN.1 Module
skipping to change at page 16, line 17 skipping to change at page 17, line 11
FROM KerberosV5-PK-INIT-SPEC { FROM KerberosV5-PK-INIT-SPEC {
iso(1) identified-organization(3) dod(6) internet(1) iso(1) identified-organization(3) dod(6) internet(1)
security(5) kerberosV5(2) modules(4) pkinit(5) }; security(5) kerberosV5(2) modules(4) pkinit(5) };
-- as defined in RFC 4556. -- as defined in RFC 4556.
id-pkinit-kdf OBJECT IDENTIFIER ::= { id-pkinit kdf(6) } id-pkinit-kdf OBJECT IDENTIFIER ::= { id-pkinit kdf(6) }
-- PKINIT KDFs -- PKINIT KDFs
id-pkinit-kdf-ah-sha1 OBJECT IDENTIFIER id-pkinit-kdf-ah-sha1 OBJECT IDENTIFIER
::= { id-pkinit-kdf sha1(1) } ::= { id-pkinit-kdf sha1(1) }
-- SP800-56A ASN.1 structured hash based KDF using SHA-1 -- SP800-56A ASN.1 structured hash-based KDF using SHA-1
id-pkinit-kdf-ah-sha256 OBJECT IDENTIFIER id-pkinit-kdf-ah-sha256 OBJECT IDENTIFIER
::= { id-pkinit-kdf sha256(2) } ::= { id-pkinit-kdf sha256(2) }
-- SP800-56A ASN.1 structured hash based KDF using SHA-256 -- SP800-56A ASN.1 structured hash-based KDF using SHA-256
id-pkinit-kdf-ah-sha512 OBJECT IDENTIFIER id-pkinit-kdf-ah-sha512 OBJECT IDENTIFIER
::= { id-pkinit-kdf sha512(3) } ::= { id-pkinit-kdf sha512(3) }
-- SP800-56A ASN.1 structured hash based KDF using SHA-512 -- SP800-56A ASN.1 structured hash-based KDF using SHA-512
id-pkinit-kdf-ah-sha384 OBJECT IDENTIFIER id-pkinit-kdf-ah-sha384 OBJECT IDENTIFIER
::= { id-pkinit-kdf sha384(4) } ::= { id-pkinit-kdf sha384(4) }
-- SP800-56A ASN.1 structured hash based KDF using SHA-384 -- SP800-56A ASN.1 structured hash-based KDF using SHA-384
TD-CMS-DIGEST-ALGORITHMS-DATA ::= SEQUENCE OF TD-CMS-DIGEST-ALGORITHMS-DATA ::= SEQUENCE OF
AlgorithmIdentifier AlgorithmIdentifier
-- Contains the list of CMS algorithm [RFC5652] -- Contains the list of CMS algorithm [RFC5652]
-- identifiers that identify the digest algorithms -- identifiers that identify the digest algorithms
-- acceptable by the KDC for signing CMS data in -- acceptable by the KDC for signing CMS data in
-- the order of decreasing preference. -- the order of decreasing preference.
TD-CERT-DIGEST-ALGORITHMS-DATA ::= SEQUENCE { TD-CERT-DIGEST-ALGORITHMS-DATA ::= SEQUENCE {
allowedAlgorithms [0] SEQUENCE OF AlgorithmIdentifier, allowedAlgorithms [0] SEQUENCE OF AlgorithmIdentifier,
skipping to change at page 17, line 20 skipping to change at page 18, line 14
partyUInfo [0] OCTET STRING, partyUInfo [0] OCTET STRING,
partyVInfo [1] OCTET STRING, partyVInfo [1] OCTET STRING,
suppPubInfo [2] OCTET STRING OPTIONAL, suppPubInfo [2] OCTET STRING OPTIONAL,
suppPrivInfo [3] OCTET STRING OPTIONAL suppPrivInfo [3] OCTET STRING OPTIONAL
} }
PkinitSuppPubInfo ::= SEQUENCE { PkinitSuppPubInfo ::= SEQUENCE {
enctype [0] Int32, enctype [0] Int32,
-- The enctype of the AS reply key. -- The enctype of the AS reply key.
as-REQ [1] OCTET STRING, as-REQ [1] OCTET STRING,
-- This contains the AS-REQ in the request. -- The DER encoding of the AS-REQ [RFC4120] from the
-- client.
pk-as-rep [2] OCTET STRING, pk-as-rep [2] OCTET STRING,
-- Contains the DER encoding of the type -- The DER encoding of the PA-PK-AS-REP [RFC4556] in the
-- PA-PK-AS-REP [RFC4556] in the KDC reply. -- KDC reply.
... ...
} }
AuthPack ::= SEQUENCE { AuthPack ::= SEQUENCE {
pkAuthenticator [0] PKAuthenticator, pkAuthenticator [0] PKAuthenticator,
clientPublicValue [1] SubjectPublicKeyInfo OPTIONAL, clientPublicValue [1] SubjectPublicKeyInfo OPTIONAL,
supportedCMSTypes [2] SEQUENCE OF AlgorithmIdentifier supportedCMSTypes [2] SEQUENCE OF AlgorithmIdentifier
OPTIONAL, OPTIONAL,
clientDHNonce [3] DHNonce OPTIONAL, clientDHNonce [3] DHNonce OPTIONAL,
..., ...,
 End of changes. 50 change blocks. 
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