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diff --git a/crypto/heimdal/doc/standardisation/draft-ietf-cat-kerberos-pk-init-03.txt b/crypto/heimdal/doc/standardisation/draft-ietf-cat-kerberos-pk-init-03.txt deleted file mode 100644 index d91c087..0000000 --- a/crypto/heimdal/doc/standardisation/draft-ietf-cat-kerberos-pk-init-03.txt +++ /dev/null @@ -1,589 +0,0 @@ - -INTERNET-DRAFT Clifford Neuman -draft-ietf-cat-kerberos-pk-init-03.txt Brian Tung -Updates: RFC 1510 ISI -expires September 30, 1997 John Wray - Digital Equipment Corporation - Ari Medvinsky - Matthew Hur - CyberSafe Corporation - Jonathan Trostle - Novell - - - Public Key Cryptography for Initial Authentication in Kerberos - - -0. Status Of this Memo - - This document is an Internet-Draft. Internet-Drafts are working - documents of the Internet Engineering Task Force (IETF), its - areas, and its working groups. Note that other groups may also - distribute working documents as Internet-Drafts. - - Internet-Drafts are draft documents valid for a maximum of six - months and may be updated, replaced, or obsoleted by other - documents at any time. It is inappropriate to use Internet-Drafts - as reference material or to cite them other than as "work in - progress." - - To learn the current status of any Internet-Draft, please check - the "1id-abstracts.txt" listing contained in the Internet-Drafts - Shadow Directories on ds.internic.net (US East Coast), - nic.nordu.net (Europe), ftp.isi.edu (US West Coast), or - munnari.oz.au (Pacific Rim). - - The distribution of this memo is unlimited. It is filed as - draft-ietf-cat-kerberos-pk-init-03.txt, and expires September 30, - 1997. Please send comments to the authors. - - -1. Abstract - - This document defines extensions (PKINIT) to the Kerberos protocol - specification (RFC 1510 [1]) to provide a method for using public - key cryptography during initial authentication. The methods - defined specify the ways in which preauthentication data fields and - error data fields in Kerberos messages are to be used to transport - public key data. - - -2. Introduction - - The popularity of public key cryptography has produced a desire for - its support in Kerberos [2]. The advantages provided by public key - cryptography include simplified key management (from the Kerberos - perspective) and the ability to leverage existing and developing - public key certification infrastructures. - - Public key cryptography can be integrated into Kerberos in a number - of ways. One is to to associate a key pair with each realm, which - can then be used to facilitate cross-realm authentication; this is - the topic of another draft proposal. Another way is to allow users - with public key certificates to use them in initial authentication. - This is the concern of the current document. - - One of the guiding principles in the design of PKINIT is that - changes should be as minimal as possible. As a result, the basic - mechanism of PKINIT is as follows: The user sends a request to the - KDC as before, except that if that user is to use public key - cryptography in the initial authentication step, his certificate - accompanies the initial request, in the preauthentication fields. - - Upon receipt of this request, the KDC verifies the certificate and - issues a ticket granting ticket (TGT) as before, except that instead - of being encrypted in the user's long-term key (which is derived - from a password), it is encrypted in a randomly-generated key. This - random key is in turn encrypted using the public key certificate - that came with the request and signed using the KDC's signature key, - and accompanies the reply, in the preauthentication fields. - - PKINIT also allows for users with only digital signature keys to - authenticate using those keys, and for users to store and retrieve - private keys on the KDC. - - The PKINIT specification may also be used for direct peer to peer - authentication without contacting a central KDC. This application - of PKINIT is described in PKTAPP [4] and is based on concepts - introduced in [5, 6]. For direct client-to-server authentication, - the client uses PKINIT to authenticate to the end server (instead - of a central KDC), which then issues a ticket for itself. This - approach has an advantage over SSL [7] in that the server does not - need to save state (cache session keys). Furthermore, an - additional benefit is that Kerberos tickets can facilitate - delegation (see [8]). - - -3. Proposed Extensions - - This section describes extensions to RFC 1510 for supporting the - use of public key cryptography in the initial request for a ticket - granting ticket (TGT). - - In summary, the following changes to RFC 1510 are proposed: - - --> Users may authenticate using either a public key pair or a - conventional (symmetric) key. If public key cryptography is - used, public key data is transported in preauthentication - data fields to help establish identity. - --> Users may store private keys on the KDC for retrieval during - Kerberos initial authentication. - - This proposal addresses two ways that users may use public key - cryptography for initial authentication. Users may present public - key certificates, or they may generate their own session key, - signed by their digital signature key. In either case, the end - result is that the user obtains an ordinary TGT that may be used for - subsequent authentication, with such authentication using only - conventional cryptography. - - Section 3.1 provides definitions to help specify message formats. - Section 3.2 and 3.3 describe the extensions for the two initial - authentication methods. Section 3.3 describes a way for the user to - store and retrieve his private key on the KDC. - - -3.1. Definitions - - Hash and encryption types will be specified using ENCTYPE tags; we - propose the addition of the following types: - - #define ENCTYPE_SIGN_DSA_GENERATE 0x0011 - #define ENCTYPE_SIGN_DSA_VERIFY 0x0012 - #define ENCTYPE_ENCRYPT_RSA_PRIV 0x0021 - #define ENCTYPE_ENCRYPT_RSA_PUB 0x0022 - - allowing further signature types to be defined in the range 0x0011 - through 0x001f, and further encryption types to be defined in the - range 0x0021 through 0x002f. - - The extensions involve new preauthentication fields. The - preauthentication data types are in the range 17 through 21. - These values are also specified along with their corresponding - ASN.1 definition. - - #define PA-PK-AS-REQ 17 - #define PA-PK-AS-REP 18 - #define PA-PK-AS-SIGN 19 - #define PA-PK-KEY-REQ 20 - #define PA-PK-KEY-REP 21 - - The extensions also involve new error types. The new error types - are in the range 227 through 229. They are: - - #define KDC_ERROR_CLIENT_NOT_TRUSTED 227 - #define KDC_ERROR_KDC_NOT_TRUSTED 228 - #define KDC_ERROR_INVALID_SIG 229 - - In the exposition below, we use the following terms: encryption key, - decryption key, signature key, verification key. It should be - understood that encryption and verification keys are essentially - public keys, and decryption and signature keys are essentially - private keys. The fact that they are logically distinct does - not preclude the assignment of bitwise identical keys. - - -3.2. Standard Public Key Authentication - - Implementation of the changes in this section is REQUIRED for - compliance with pk-init. - - It is assumed that all public keys are signed by some certification - authority (CA). The initial authentication request is sent as per - RFC 1510, except that a preauthentication field containing data - signed by the user's signature key accompanies the request: - - PA-PK-AS-REQ ::- SEQUENCE { - -- PA TYPE 17 - signedPKAuth [0] SignedPKAuthenticator, - userCert [1] SEQUENCE OF Certificate OPTIONAL, - -- the user's certificate - -- optionally followed by that - -- certificate's certifier chain - trustedCertifiers [2] SEQUENCE OF PrincipalName OPTIONAL - -- CAs that the client trusts - } - - SignedPKAuthenticator ::= SEQUENCE { - pkAuth [0] PKAuthenticator, - pkAuthSig [1] Signature, - -- of pkAuth - -- using user's signature key - } - - PKAuthenticator ::= SEQUENCE { - cusec [0] INTEGER, - -- for replay prevention - ctime [1] KerberosTime, - -- for replay prevention - nonce [2] INTEGER, - -- binds response to this request - kdcName [3] PrincipalName, - clientPubValue [4] SubjectPublicKeyInfo OPTIONAL, - -- for Diffie-Hellman algorithm - } - - Signature ::= SEQUENCE { - signedHash [0] EncryptedData - -- of type Checksum - -- encrypted under signature key - } - - Checksum ::= SEQUENCE { - cksumtype [0] INTEGER, - checksum [1] OCTET STRING - } -- as specified by RFC 1510 - - SubjectPublicKeyInfo ::= SEQUENCE { - algorithm [0] algorithmIdentifier, - subjectPublicKey [1] BIT STRING - } -- as specified by the X.509 recommendation [9] - - Certificate ::= SEQUENCE { - CertType [0] INTEGER, - -- type of certificate - -- 1 = X.509v3 (DER encoding) - -- 2 = PGP (per PGP draft) - CertData [1] OCTET STRING - -- actual certificate - -- type determined by CertType - } - - Note: If the signature uses RSA keys, then it is to be performed - as per PKCS #1. - - The PKAuthenticator carries information to foil replay attacks, - to bind the request and response, and to optionally pass the - client's Diffie-Hellman public value (i.e. for using DSA in - combination with Diffie-Hellman). The PKAuthenticator is signed - with the private key corresponding to the public key in the - certificate found in userCert (or cached by the KDC). - - In the PKAuthenticator, the client may specify the KDC name in one - of two ways: 1) a Kerberos principal name, or 2) the name in the - KDC's certificate (e.g., an X.500 name, or a PGP name). Note that - case #1 requires that the certificate name and the Kerberos principal - name be bound together (e.g., via an X.509v3 extension). - - The userCert field is a sequence of certificates, the first of which - must be the user's public key certificate. Any subsequent - certificates will be certificates of the certifiers of the user's - certificate. These cerificates may be used by the KDC to verify the - user's public key. This field is empty if the KDC already has the - user's certifcate. - - The trustedCertifiers field contains a list of certification - authorities trusted by the client, in the case that the client does - not possess the KDC's public key certificate. - - Upon receipt of the AS_REQ with PA-PK-AS-REQ pre-authentication - type, the KDC attempts to verify the user's certificate chain - (userCert), if one is provided in the request. This is done by - verifying the certification path against the KDC's policy of - legitimate certifiers. This may be based on a certification - hierarchy, or it may be simply a list of recognized certifiers in a - system like PGP. If the certification path does not match one of - the KDC's trusted certifiers, the KDC sends back an error message of - type KDC_ERROR_CLIENT_NOT_TRUSTED, and it includes in the error data - field a list of its own trusted certifiers, upon which the client - resends the request. - - If trustedCertifiers is provided in the PA-PK-AS-REQ, the KDC - verifies that it has a certificate issued by one of the certifiers - trusted by the client. If it does not have a suitable certificate, - the KDC returns an error message of type KDC_ERROR_KDC_NOT_TRUSTED - to the client. - - If a trust relationship exists, the KDC then verifies the client's - signature on PKAuthenticator. If that fails, the KDC returns an - error message of type KDC_ERROR_INVALID_SIG. Otherwise, the KDC - uses the timestamp in the PKAuthenticator to assure that the request - is not a replay. The KDC also verifies that its name is specified - in PKAuthenticator. - - Assuming no errors, the KDC replies as per RFC 1510, except that it - encrypts the reply not with the user's key, but with a random key - generated only for this particular response. This random key - is sealed in the preauthentication field: - - PA-PK-AS-REP ::= SEQUENCE { - -- PA TYPE 18 - kdcCert [0] SEQUENCE OF Certificate OPTIONAL, - -- the KDC's certificate - -- optionally followed by that - -- certificate's certifier chain - encPaReply [1] EncryptedData, - -- of type PaReply - -- using either the client public - -- key or the Diffie-Hellman key - -- specified by SignedDHPublicValue - signedDHPublicValue [2] SignedDHPublicValue OPTIONAL - } - - - PaReply ::= SEQUENCE { - replyEncKeyPack [0] ReplyEncKeyPack, - replyEncKeyPackSig [1] Signature, - -- of replyEncKeyPack - -- using KDC's signature key - } - - ReplyEncKeyPack ::= SEQUENCE { - replyEncKey [0] EncryptionKey, - -- used to encrypt main reply - nonce [1] INTEGER - -- binds response to the request - -- passed in the PKAuthenticator - } - - SignedDHPublicValue ::= SEQUENCE { - dhPublicValue [0] SubjectPublicKeyInfo, - dhPublicValueSig [1] Signature - -- of dhPublicValue - -- using KDC's signature key - } - - The kdcCert field is a sequence of certificates, the first of which - must have as its root certifier one of the certifiers sent to the - KDC in the PA-PK-AS-REQ. Any subsequent certificates will be - certificates of the certifiers of the KDC's certificate. These - cerificates may be used by the client to verify the KDC's public - key. This field is empty if the client did not send to the KDC a - list of trusted certifiers (the trustedCertifiers field was empty). - - Since each certifier in the certification path of a user's - certificate is essentially a separate realm, the name of each - certifier shall be added to the transited field of the ticket. The - format of these realm names shall follow the naming constraints set - forth in RFC 1510 (sections 7.1 and 3.3.3.1). Note that this will - require new nametypes to be defined for PGP certifiers and other - types of realms as they arise. - - The KDC's certificate must bind the public key to a name derivable - from the name of the realm for that KDC. The client then extracts - the random key used to encrypt the main reply. This random key (in - encPaReply) is encrypted with either the client's public key or - with a key derived from the DH values exchanged between the client - and the KDC. - - -3.3. Digital Signature - - Implementation of the changes in this section are OPTIONAL for - compliance with pk-init. - - We offer this option with the warning that it requires the client to - generate a random key; the client may not be able to guarantee the - same level of randomness as the KDC. - - If the user registered a digital signature key with the KDC instead - of an encryption key, then a separate exchange must be used. The - client sends a request for a TGT as usual, except that it (rather - than the KDC) generates the random key that will be used to encrypt - the KDC response. This key is sent to the KDC along with the - request in a preauthentication field: - - PA-PK-AS-SIGN ::= SEQUENCE { - -- PA TYPE 19 - encSignedKeyPack [0] EncryptedData - -- of SignedKeyPack - -- using the KDC's public key - } - - SignedKeyPack ::= SEQUENCE { - signedKey [0] KeyPack, - signedKeyAuth [1] PKAuthenticator, - signedKeySig [2] Signature - -- of signedKey.signedKeyAuth - -- using user's signature key - } - - KeyPack ::= SEQUENCE { - randomKey [0] EncryptionKey, - -- will be used to encrypt reply - nonce [1] INTEGER - } - - where the nonce is copied from the request. - - Upon receipt of the PA-PK-AS-SIGN, the KDC decrypts then verifies - the randomKey. It then replies as per RFC 1510, except that the - reply is encrypted not with a password-derived user key, but with - the randomKey sent in the request. Since the client already knows - this key, there is no need to accompany the reply with an extra - preauthentication field. The transited field of the ticket should - specify the certification path as described in Section 3.2. - - -3.4. Retrieving the Private Key From the KDC - - Implementation of the changes in this section is RECOMMENDED for - compliance with pk-init. - - When the user's private key is not stored local to the user, he may - choose to store the private key (normally encrypted using a - password-derived key) on the KDC. We provide this option to present - the user with an alternative to storing the private key on local - disk at each machine where he expects to authenticate himself using - pk-init. It should be noted that it replaces the added risk of - long-term storage of the private key on possibly many workstations - with the added risk of storing the private key on the KDC in a - form vulnerable to brute-force attack. - - In order to obtain a private key, the client includes a - preauthentication field with the AS-REQ message: - - PA-PK-KEY-REQ ::= SEQUENCE { - -- PA TYPE 20 - patimestamp [0] KerberosTime OPTIONAL, - -- used to address replay attacks. - pausec [1] INTEGER OPTIONAL, - -- used to address replay attacks. - nonce [2] INTEGER, - -- binds the reply to this request - privkeyID [3] SEQUENCE OF KeyID OPTIONAL - -- constructed as a hash of - -- public key corresponding to - -- desired private key - } - - KeyID ::= SEQUENCE { - KeyIdentifier [0] OCTET STRING - } - - The client may request a specific private key by sending the - corresponding ID. If this field is left empty, then all - private keys are returned. - - If all checks out, the KDC responds as described in the above - sections, except that an additional preauthentication field, - containing the user's private key, accompanies the reply: - - PA-PK-KEY-REP ::= SEQUENCE { - -- PA TYPE 21 - nonce [0] INTEGER, - -- binds the reply to the request - KeyData [1] SEQUENCE OF KeyPair - } - - KeyPair ::= SEQUENCE { - privKeyID [0] OCTET STRING, - -- corresponding to encPrivKey - encPrivKey [1] OCTET STRING - } - - -3.4.1. Additional Protection of Retrieved Private Keys - - We solicit discussion on the following proposal: that the client may - optionally include in its request additional data to encrypt the - private key, which is currently only protected by the user's - password. One possibility is that the client might generate a - random string of bits, encrypt it with the public key of the KDC (as - in the SignedKeyPack, but with an ordinary OCTET STRING in place of - an EncryptionKey), and include this with the request. The KDC then - XORs each returned key with this random bit string. (If the bit - string is too short, the KDC could either return an error, or XOR - the returned key with a repetition of the bit string.) - - In order to make this work, additional means of preauthentication - need to be devised in order to prevent attackers from simply - inserting their own bit string. One way to do this is to store - a hash of the password-derived key (the one used to encrypt the - private key). This hash is then used in turn to derive a second - key (called the hash-key); the hash-key is used to encrypt an ASN.1 - structure containing the generated bit string and a nonce value - that binds it to the request. - - Since the KDC possesses the hash, it can generate the hash-key and - verify this (weaker) preauthentication, and yet cannot reproduce - the private key itself, since the hash is a one-way function. - - -4. Logistics and Policy Issues - - We solicit discussion on how clients and KDCs should be configured - in order to determine which of the options described above (if any) - should be used. One possibility is to set the user's database - record to indicate that authentication is to use public key - cryptography; this will not work, however, in the event that the - client needs to know before making the initial request. - -5. Compatibility with One-Time Passcodes - - We solicit discussion on how the protocol changes proposed in this - draft will interact with the proposed use of one-time passcodes - discussed in draft-ietf-cat-kerberos-passwords-00.txt. - - -6. Strength of Cryptographic Schemes - - In light of recent findings on the strength of MD5 and DES, - we solicit discussion on which encryption types to incorporate - into the protocol changes. - - -7. Bibliography - - [1] J. Kohl, C. Neuman. The Kerberos Network Authentication - Service (V5). Request for Comments: 1510 - - [2] B.C. Neuman, Theodore Ts'o. Kerberos: An Authentication Service - for Computer Networks, IEEE Communications, 32(9):33-38. - September 1994. - - [3] A. Medvinsky, M. Hur. Addition of Kerberos Cipher Suites to - Transport Layer Security (TLS). - draft-ietf-tls-kerb-cipher-suites-00.txt - - [4] A. Medvinsky, M. Hur, B. Clifford Neuman. Public Key Utilizing - Tickets for Application Servers (PKTAPP). - draft-ietf-cat-pktapp-00.txt - - [5] M. Sirbu, J. Chuang. Distributed Authentication in Kerberos Using - Public Key Cryptography. Symposium On Network and Distributed System - Security, 1997. - - [6] B. Cox, J.D. Tygar, M. Sirbu. NetBill Security and Transaction - Protocol. In Proceedings of the USENIX Workshop on Electronic Commerce, - July 1995. - - [7] Alan O. Freier, Philip Karlton and Paul C. Kocher. - The SSL Protocol, Version 3.0 - IETF Draft. - - [8] B.C. Neuman, Proxy-Based Authorization and Accounting for - Distributed Systems. In Proceedings of the 13th International - Conference on Distributed Computing Systems, May 1993 - - [9] ITU-T (formerly CCITT) - Information technology - Open Systems Interconnection - - The Directory: Authentication Framework Recommendation X.509 - ISO/IEC 9594-8 - - -8. Acknowledgements - - Some of the ideas on which this proposal is based arose during - discussions over several years between members of the SAAG, the IETF - CAT working group, and the PSRG, regarding integration of Kerberos - and SPX. Some ideas have also been drawn from the DASS system. - These changes are by no means endorsed by these groups. This is an - attempt to revive some of the goals of those groups, and this - proposal approaches those goals primarily from the Kerberos - perspective. Lastly, comments from groups working on similar ideas - in DCE have been invaluable. - - -9. Expiration Date - - This draft expires September 30, 1997. - - -10. Authors - - Clifford Neuman - Brian Tung - USC Information Sciences Institute - 4676 Admiralty Way Suite 1001 - Marina del Rey CA 90292-6695 - Phone: +1 310 822 1511 - E-mail: {bcn, brian}@isi.edu - - John Wray - Digital Equipment Corporation - 550 King Street, LKG2-2/Z7 - Littleton, MA 01460 - Phone: +1 508 486 5210 - E-mail: wray@tuxedo.enet.dec.com - - Ari Medvinsky - Matthew Hur - CyberSafe Corporation - 1605 NW Sammamish Road Suite 310 - Issaquah WA 98027-5378 - Phone: +1 206 391 6000 - E-mail: {ari.medvinsky, matt.hur}@cybersafe.com - - Jonathan Trostle - Novell - E-mail: jonathan.trostle@novell.com |
