Network Working Group M. Eisler Internet Draft Sun Microsystems, Inc. Document: draft-ietf-cat-lipkey-01.txt June 1999 LIPKEY - A Low Infrastructure Public Key Mechanism Using SPKM Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Abstract This memorandum describes a method whereby one can use GSS-API [RFC2078] to supply a secure channel between a client and server, authenticating the client with a password, and server with a public key certificate. As such, it is analogous to the common low infrastructure usage of the Transport Layer Service (TLS) protocol [RFC2246]. The method leverages the existing Simple Public Key Mechanism (SPKM) [RFC2025], and is specified as a separate GSS-API mechanism (LIPKEY) layered on top of SPKM. Expires: December 1999 [Page 1]
INTERNET-DRAFT LIPKEY June 1999 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. LIPKEY's Requirements of SPKM . . . . . . . . . . . . . . . . 4 2.1. Mechanism Type . . . . . . . . . . . . . . . . . . . . . . . 4 2.2. Name Type . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.3. Algorithms . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.4. Context Establish Tokens . . . . . . . . . . . . . . . . . . 6 2.4.1. REQ-TOKEN Content Requirements . . . . . . . . . . . . . . 6 2.4.1.1. algId and req-integrity . . . . . . . . . . . . . . . . 7 2.4.1.2. Req-contents . . . . . . . . . . . . . . . . . . . . . . 7 2.4.1.2.1. Options . . . . . . . . . . . . . . . . . . . . . . . 7 2.4.1.2.2. Conf-Algs . . . . . . . . . . . . . . . . . . . . . . 7 2.4.1.2.3. Intg-Algs . . . . . . . . . . . . . . . . . . . . . . 7 2.4.2. REP-TI-TOKEN Content Requirements . . . . . . . . . . . . 7 2.4.2.1. algId . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.4.2.2. rep-ti-integ . . . . . . . . . . . . . . . . . . . . . . 8 3. How LIPKEY Uses SPKM . . . . . . . . . . . . . . . . . . . . . 8 3.1. Tokens . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 3.2. Initiator . . . . . . . . . . . . . . . . . . . . . . . . . 8 3.2.1. GSS_Import_name . . . . . . . . . . . . . . . . . . . . . 8 3.2.2. GSS_Acquire_cred . . . . . . . . . . . . . . . . . . . . . 8 3.2.3. GSS_Init_sec_context . . . . . . . . . . . . . . . . . . . 8 3.2.3.1. LIPKEY Caller Specified anon_req_flag as TRUE . . . . . 9 3.2.3.2. LIPKEY Caller Specified anon_req_flag as FALSE . . . . 10 3.2.4. Other operations . . . . . . . . . . . . . . . . . . . . 11 3.3. Target . . . . . . . . . . . . . . . . . . . . . . . . . . 11 3.3.1. GSS_Import_name . . . . . . . . . . . . . . . . . . . . 11 3.3.2. GSS_Acquire_cred . . . . . . . . . . . . . . . . . . . . 11 3.3.3. GSS_Accept_sec_context . . . . . . . . . . . . . . . . . 11 4. LIPKEY Description . . . . . . . . . . . . . . . . . . . . . 12 4.1. Mechanism Type . . . . . . . . . . . . . . . . . . . . . . 12 4.2. Name Types . . . . . . . . . . . . . . . . . . . . . . . . 12 4.3. Token Formats . . . . . . . . . . . . . . . . . . . . . . 12 4.3.1. Context Tokens . . . . . . . . . . . . . . . . . . . . . 12 4.3.1.1. Context Tokens Prior to SPKM-3 Context Establishment . 12 4.3.1.2. Post-SPKM-3 Context Establishment Token . . . . . . . 13 4.3.2. Tokens from GSS_GetMIC and GSS_Wrap . . . . . . . . . . 13 4.4. Quality of Protection . . . . . . . . . . . . . . . . . . 14 5. Security Considerations . . . . . . . . . . . . . . . . . . 15 5.1. Password Management . . . . . . . . . . . . . . . . . . . 15 5.2. Certificate Authorities . . . . . . . . . . . . . . . . . 15 References . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 17 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 17 Expires: December 1999 [Page 2]
INTERNET-DRAFT LIPKEY June 1999 1. Introduction 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]. This memorandum describes a new security mechanism under the GSS-API called the Low Infrastructure Public Key Mechanism (LIPKEY). GSS-API provides a way for an application protocol to implement authentication, integrity, and privacy. TLS is another way. While TLS is in many ways simpler for an application to incorporate than GSS- API, there are situations where GSS-API might be more suitable. Certainly this is the case with application protocols that run over connectionless protocols. It is also the case with application protocols such as ONC RPC [RFC1831] [RFC2203], which have their own security architecture, and so don't easily mesh with a protocol like TLS that is implemented as a layer that encapsulates the upper layer application protocol. GSS-API allows the application protocol to encapsulate as much of the application protocol as necessary. Despite the flexibility of GSS-API, it compares unfavorably with TLS with respect to the perception of the amount of infrastructure required to deploy it. The better known GSS-API mechanisms, Kerberos V5 [RFC1964] and SPKM require a great deal of infrastructure to set up. Compare this to the typical TLS deployment scenario, which consists of a client with no public key certificate accessing a server with a public key certificate. The client: * obtains the server's certificate, * verifies that it was signed by a trusted certificate authority (CA), * generates a random session symmetric key, * encrypts the session key with the server's public key, and * sends the encrypted session key to the server. At this point, the client and server have a secure channel. The client can then provide a user name and password to the server to authenticate the client. For example, when TLS is being used with the http protocol, once there is a secure channel, the http server will present the client with an html page that prompts for a user name and password. This information is then encrypted with the session key and sent to the server. The server then authenticates the client. Note that the client is not required to have a certificate to Expires: December 1999 [Page 3]
INTERNET-DRAFT LIPKEY June 1999 identify and authenticate it to the server. The only security infrastructure required, other than a TLS implementation, is a public key certificate and password database on the server. Most operating systems that the http server would run on already have a native password database, so the net additional infrastructure is a server certificate. Hence the term "low infrastructure security model" to identify this typical TLS deployment scenario. By using unilateral authentication, and using a mechanism resembling the SPKM-1 mechanism type, SPKM can offer many aspects of the previously described low infrastructure security model. An application that uses GSS-API is certainly free to use GSS-API's GSS_Wrap() routine to encrypt a user name and password and send them to the server, for it to decrypt and verify. Applications often have application protocols associated with them, and there might not be any provision in the protocol to specify a password. Layering a thin GSS-API mechanism over a mechanism resembling SPKM-1 can mitigate this problem. This can be a useful approach to avoid versioning applications that have already bound to GSS-API, assuming the applications have not been written to statically bind to specific GSS-API mechanisms. The remainder of this memorandum defines the thin mechanism: the Low Infrastructure Public Key Mechanism (LIPKEY). 2. LIPKEY's Requirements of SPKM SPKM-1 with unilateral authentication is close to the desired low infrastructure model described earlier. This section describes some additional changes to how SPKM-1 operates in order to realize the low infrastructure model. These changes include some minor changes in semantics. While it would be possible to implement these semantic changes within an SPKM-1 implementation (including using the same mechanism type OID as SPKM-1), the set of changes stretch the interpretation of RFC 2025 to the point where compatibility would be in danger. A new mechanism type, called SPKM-3, is warranted. LIPKEY requires that the SPKM implementation support SPKM-3. SPKM-3 is equivalent to SPKM-1, except as described in the remainder of this section. 2.1. Mechanism Type SPKM-3 has a different mechanism type OID from SPKM-1. The SPKM-3 message type's OID is not yet defined. 2.2. Name Type RFC 2025 defines no required name types of SPKM. LIPKEY requires that Expires: December 1999 [Page 4]
INTERNET-DRAFT LIPKEY June 1999 the SPKM-3 implementation support all the mechanism independent name types in RFC 2078. 2.3. Algorithms RFC 2025 defines various algorithms for integrity, confidentiality, key establishment, and subkey derivation. SPKM is designed to be extensible with regard to new algorithms. In order for LIPKEY to work correctly and securely, the following algorithms MUST be implemented in SPKM-3: * Integrity algorithms (I-ALG) NULL-MAC Because the initiator may not have a certificate for itself, nor for the target, it is not possible for it to calculate an Integrity value in the initiator's REQ-TOKEN that is sent to the target. So we define, in ASN.1 [CCITT] syntax, a null I- ALG that returns a zero length bit string regardless of the input passed to it: NULL-MAC OBJECT IDENTIFIER ::= { -- OID to be defined } DES-MAC The other consequence of the initiator not having a certificate is that it cannot use the md5WithRSAEncryption integrity algorithm. RFC 2025 notes that the DES-MAC I-ALG is RECOMMENDED. LIPKEY must have a MAC algorithm present in SPKM-3, and so SPKM-3 implementations MUST support the DES- MAC I-ALG. md5WithRSAEncryption We still need, and so continue to REQUIRE, md5WithRSAEncryption for the checksumming of the target's context token. Note that due to intellectual property considerations, a future revision of this internet draft may mandate another integrity algorithm in place of md5WithRSAEncryption, although it is anticipated md5WithRSAEncryption will still be RECOMMENDED. * Confidentiality algorithm (C-ALG). RFC 2025 does not have a MANDATORY confidentiality algorithm, Expires: December 1999 [Page 5]
INTERNET-DRAFT LIPKEY June 1999 and instead has RECOMMENDED a 56 bit DES algorithm. Since the LIPKEY initiator needs to send a password to the target, and since 56 bit DES has been demonstrated as inadequate [EFF], LIPKEY needs stronger encryption. Thus, SPKM-3 MUST support this triple DES algorithm: DES-EDE3-CBC OBJECT IDENTIFIER ::= { iso(1) member-body(2) US(840) rsadsi(113549) encryptionAlgorithm(3) 7 } The reference for the algorithm OID of the DES-EDE3-CBC algorithm is [RSA]. The reference for the algorithm's description is believed to be [X9.52]. * Key Establishment Algorithm (K-ALG) RFC 2025 lists dhKeyAgreement [PKCS-3] as an apparently optional algorithm. As will be described later, the required RSAEncryption key establishment algorithm is of no use for a low infrastructure security mechanism as defined by this memorandum. Hence, in SPKM-3, dhKeyAgreement is a REQUIRED key establishment algorithm: dhKeyAgreement OBJECT IDENTIFIER ::= { iso(1) member-body(2) US(840) rsadsi(113549) pkcs(1) pkcs-3(3) 1 } The REQUIRED Key Establishment (K-ALG), Integrity (I-ALG) and One-Way Functions for Subkey Derivation (O-ALG) algorithms listed in RFC 2025 continue to be REQUIRED. 2.4. Context Establish Tokens RFC 2025 sets up a context with an initiator first token (REQ-TOKEN), a target reply (REP-TI-TOKEN), and finally an initiator second token (REP-TI-TOKEN) to reply to the target's reply. Since LIPKEY uses SPKM-3 with unilateral authentication, the REP-TI-TOKEN is not used. LIPKEY has certain requirements on the contents of the REQ-TOKEN and REP-TI-TOKEN, but the syntax of the SPKM-3 tokens is not different from RFC 2025's SPKM-1 tokens. 2.4.1. REQ-TOKEN Content Requirements Expires: December 1999 [Page 6]
INTERNET-DRAFT LIPKEY June 1999 2.4.1.1. algId and req-integrity If the SPKM-3 initiator cannot calculate a req-integrity field due to the lack of a target certificate, it MUST use the NULL-MAC I-ALG described earlier in this memorandum. This will produce a zero length bit string in the Integrity field. 2.4.1.2. Req-contents Because RFC 2025 requires that the RSAEncryption K-ALG be present, SPKM-1 must be able to map the target (targ-name) to its public key certificate, and thus SPKM can use the RSAEncryption algorithm to fill in the key-estb-req field. Because LIPKEY assumes a low infrastructure deployment, SPKM-3 MUST be prepared to be unable to map the targ-name field of the Req-contents field. This is a contradiction which is resolved by requiring SPKM-3 to support the dhKeyAgreement algorithm. Note that if an SPKM-3 implementation tries to map the target to a certificate, and succeeds, it is free to use the RSAEncryption K-ALG algorithm. It is also free to use an algID other than NULL-MAC in the REQ-TOKEN type. 2.4.1.2.1. Options SPKM-3 implementations MUST set the target-certif-data-required bit to 1 if the only K-ALG in the key-estb-set field of Req-contents is dhKeyAgreement. This would normally occur if the SPKM-3 implementation cannot resolve the target name to a certificate. 2.4.1.2.2. Conf-Algs If the SPKM-3 implementation supports an algorithm weaker than DES- EDE3-CBC, DES-EDE3-CBC MUST be listed before the weaker algorithms to encourage the target to negotiate the stronger algorithm. 2.4.1.2.3. Intg-Algs Because the initiator will be anonymous (at the SPKM-3 level) and will not have a certificate for itself, the initiator cannot use an integrity algorithm that supports non-repudiation. 2.4.2. REP-TI-TOKEN Content Requirements With the previously described requirements on REQ-TOKEN, the contents of SPKM-3's REP-TI-TOKEN can for the most part be derived from the specification in RFC 2025. The exceptions are the algId and rep-ti- integ fields. Expires: December 1999 [Page 7]
INTERNET-DRAFT LIPKEY June 1999 2.4.2.1. algId The SPKM-3 target MUST NOT use a NULL-MAC I-ALG; it MUST use md5WithRSAEncryption. Note that this may change in a future revision of this internet draft due to intellectual property issues. 2.4.2.2. rep-ti-integ If the req-token has an algId of NULL-MAC, then the target MUST compute the rep-ti-integ on the concatenation of the req-contents and rep-ti-contents. 3. How LIPKEY Uses SPKM 3.1. Tokens LIPKEY will invoke SPKM-3 to produce SPKM tokens. Since the mechanism that the application uses is LIPKEY, LIPKEY will wrap some of the SPKM-3 tokens with LIPKEY prefixes. The exact definition of the tokens is described later in this memorandum. 3.2. Initiator 3.2.1. GSS_Import_name The initiator uses GSS_Import_name to import the target's name, typically, but not necessarily, using the GSS_C_NT_HOSTBASED_SERVICE name type. Ultimately, the output of GSS_Import_name will apply to an SPKM-3 mechanism type because a LIPKEY target is an SPKM-3 target. 3.2.2. GSS_Acquire_cred The initiator calls GSS_Acquire_cred. The credentials that are acquired are LIPKEY credentials, a user name and password. How the user name and password is acquired is dependent upon the operating environment. A application that invokes GSS_Acquire_cred() while the application's user has a graphical user interface running might trigger the appearance of a pop up window that prompts for the information. A application embedded into the operating system, such as an NFS [Sandberg] client implemented as a native file system might broadcast a message to the user's terminals telling him to invoke a command that prompts for the information. 3.2.3. GSS_Init_sec_context When a program invokes GSS_Init_sec_context on the LIPKEY mechanism Expires: December 1999 [Page 8]
INTERNET-DRAFT LIPKEY June 1999 type, if the context handle is NULL, the LIPKEY mechanism will in turn invoke GSS_Init_sec_context on an SPKM-3 mechanism implemented according to the requirements described previously. This call to SPKM-3 MUST have the following attributes: * claimant_cred_handle is NULL * mutual_req_flag is FALSE * anon_req_flag is TRUE * input_token is NULL * mech_type is the OID of the SPKM-3 mechanism Keep in mind the above attributes are in the GSS_Init_sec_context call from the LIPKEY mechanism down to the SPKM-3 mechanism. There are no special restrictions placed on the application invoking LIPKEY's GSS_Init_sec_context routine. All other arguments are derived from the LIPKEY GSS_Init_sec_context arguments. The call to the SPKM-3 GSS_Init_sec_context will create an SPKM-3 context handle. The remainder of the description of the LIPKEY GSS_Init_sec_context call depends on whether the caller of the LIPKEY GSS_Init_sec_context sets anon_req_flag to TRUE or FALSE. 3.2.3.1. LIPKEY Caller Specified anon_req_flag as TRUE If the caller of LIPKEY's GSS_Init_sec_context sets anon_req_flag to TRUE, it MUST return to the LIPKEY caller all the outputs from the SPKM-3 GSS_Init_sec_context call, including the output_context_handle, output_token, and mech_type. In this way, LIPKEY now "gets out of the way" of GSS-API processing between the application and SPKM-3, because nothing in the returned outputs relates to LIPKEY. This is necessary, because LIPKEY context tokens do not have provision for specifying anonymous initiators. This is because SPKM-3 is sufficient for purpose of supporting anonymous initiators in a low infrastructure environment. Clearly, when the LIPKEY caller desires anonymous authentication, LIPKEY does not add any value, but it is simpler to support the feature, than to insist the caller directly use SPKM-3. If all goes well, the caller of LIPKEY will be returned a major status of GSS_S_CONTINUE_NEEDED via SPKM-3, and so the caller of LIPKEY will send the output_token to the target. The caller of LIPKEY then receives the response token from the target, and directly invokes the SPKM-3 GSS_Init_sec_context. Upon return, the major Expires: December 1999 [Page 9]
INTERNET-DRAFT LIPKEY June 1999 status should be GSS_S_COMPLETE. 3.2.3.2. LIPKEY Caller Specified anon_req_flag as FALSE The LIPKEY mechanism will need to allocate a context handle for itself, and record in the LIPKEY context handle the SPKM-3 context handle that was returned in the output_context_handle parameter from the call to the SPKM-3 GSS_Init_sec_context routine. The LIPKEY GSS_Init_sec_context routine will return in output_context_handle the LIPKEY context handle, and in mech_type, the LIPKEY mechanism type. The output_token is as defined later in this memorandum, in the subsection entitled "Context Tokens Prior to SPKM-3 Context Establishment." All the other returned outputs will be those that the SPKM-3 GSS_Init_sec_context routine returned to LIPKEY. If all went well, the SPKM-3 mechanism will have returned a major status of GSS_S_CONTINUE_NEEDED. The caller of the LIPKEY GSS_Init_sec_context routine will see a major status of GSS_S_CONTINUE_NEEDED, and so the caller of LIPKEY will send the output_token to the target. The caller of LIPKEY then receives the target's response token, and invokes the LIPKEY GSS_Init_sec_context routine for a second time. LIPKEY then invokes the SPKM-3 GSS_Init_sec_context for a second time and upon return, the major status should be GSS_S_COMPLETE. While SPKM-3's context establishment is now complete, LIPKEY's context establishment is not yet complete, because the initiator must send to the target the user name and password that was passed to it via the claimant_cred_handle on the first call to the LIPKEY GSS_Init_sec_context routine. LIPKEY uses the established SPKM-3 context handle as the input to GSS_Wrap (with conf_req_flag set to TRUE) to encrypt what the claimant_cred_handle refers to (user name and password), and returns that as the output token to the caller of LIPKEY (provided the conf_state output from call to the SPKM-3 GSS_Wrap is TRUE), along with a major status of GSS_S_CONTINUE_NEEDED. The caller of LIPKEY sends its second token to the target, and waits for either a GSS_S_COMPLETE response from the target, indicating that the user name and password was accepted, or an error indicating rejection of the user name and password (GSS_NO_CRED), or some other appropriate error. The SPKM-3 context remains established while the LIPKEY context is established. If the SPKM-3 context expires before the LIPKEY context is destroyed, the LIPKEY implementation should expire the LIPKEY context and return the appropriate error on the next GSS-API operation. Expires: December 1999 [Page 10]
INTERNET-DRAFT LIPKEY June 1999 3.2.4. Other operations For other operations, the LIPKEY context acts as a pass through to the SPKM-3 context. Operations that affect or inquire context state, such as GSS_Delete_sec_context, GSS_Export_sec_context, GSS_Import_sec_context, and GSS_Inquire_context will require a pass through to the SPKM-3 context and a state modification of the LIPKEY context. 3.3. Target 3.3.1. GSS_Import_name As with the initiator, the imported name will be that of the target. 3.3.2. GSS_Acquire_cred The acceptor calls the LIPKEY GSS_Acquire_cred routine to get a credential for an SPKM-3 target, via the SPKM-3 GSS_Acquire_cred routine. The desired_name is the output_name from GSS_Import_name. 3.3.3. GSS_Accept_sec_context When a program invokes GSS_Accept_sec_context on the LIPKEY mechanism type, if the context handle is NULL, the LIPKEY mechanism will in turn invoke GSS_Accept_sec_context on an SPKM-3 mechanism implemented according the requirements described previously. This call to SPKM-3 is no different than what one would expect for a layered call to GSS_Accept_sec_context. If all goes well, the SPKM-3 GSS_Accept_sec_context call succeeds with GSS_S_COMPLETE, and the LIPKEY GSS_Accept_sec_context call returns the output_token to the caller, but with a major status of GSS_S_CONTINUE_NEEDED because the LIPKEY initiator is still expected to send the user name and password. Once the SPKM-3 context is in a GSS_S_COMPLETE state, the next token the target receives will contain the user name and password, wrapped by the output of an SPKM-3 GSS_Wrap call. The target invokes the LIPKEY GSS_Accept_sec_context, which in turn invokes the SPKM-3 GSS_Unwrap routine. The LIPKEY GSS_Accept_sec_context routine then compares the user name and password with its user name name and password database. If the initiator's user name and password are valid, GSS_S_COMPLETE is returned to the caller. Otherwise GSS_NO_CRED is returned. In either case, a zero length output_token is returned to the caller. The target should send the major status to the initiator and expect no more context tokens for that context. Expires: December 1999 [Page 11]
INTERNET-DRAFT LIPKEY June 1999 4. LIPKEY Description 4.1. Mechanism Type The Object Identifier for LIPKEY is to be defined. 4.2. Name Types LIPKEY uses only the mechanism independent name types defined in RFC 2078. All the name types defined in RFC 2078 are REQUIRED. 4.3. Token Formats 4.3.1. Context Tokens GSS-API defines the context tokens as: InitialContextToken ::= -- option indication (delegation, etc.) indicated within -- mechanism-specific token [APPLICATION 0] IMPLICIT SEQUENCE { thisMech MechType, innerContextToken ANY DEFINED BY thisMech -- contents mechanism-specific -- ASN.1 structure not required } SubsequentContextToken ::= innerContextToken ANY -- interpretation based on predecessor InitialContextToken -- ASN.1 structure not required The contents of the innerContextToken depend on whether the SPKM-3 context is established or not. 4.3.1.1. Context Tokens Prior to SPKM-3 Context Establishment In a LIPKEY InitialContextToken, thisMech will be the Object identifier for LIPKEY. However, as long as LIPKEY has not established the SPKM-3 mechanism, the innerContextToken for both the InitialContextToken and the SubsequentContextToken will be the output of an SPKM-3 GSS_Init_sec_context or GSS_Accept_sec_context. So the LIPKEY innerContextToken would be either: * An InitialContextToken, with thisMech set to the object identifier for SPKM-3, with innerContextToken defined to be an SPKMInnerContextToken, as defined in RFC 2025. Expires: December 1999 [Page 12]
INTERNET-DRAFT LIPKEY June 1999 * A SubsequentContextToken, with innerContextToken defined to be SPKMInnerContextToken 4.3.1.2. Post-SPKM-3 Context Establishment Token Once the SPKM-3 context is established, there is just one token sent from the initiator to the target, and no token returned to initiator. This token is the result of a GSS_Wrap (conf_req is set to TRUE) of a user name and password by the SPKM-3 context. This is the SPKM-WRAP token and is partially reproduced here from RFC 2025: SPKM-WRAP ::= SEQUENCE { wrap-header Wrap-Header, wrap-body Wrap-Body } Wrap-Body ::= SEQUENCE { int-cksum BIT STRING, -- Checksum of header and data, -- calculated according to -- algorithm specified in int-alg -- field of wrap-header data BIT STRING -- encrypted data. } The "data" field of Wrap-Body is contains the result of encrypting this type: UserName-Password ::= SEQUENCE { user-name OCTET STRING, -- each octet is an octet of a -- UTF-8 [RFC2279] string password OCTET STRING -- each octet is an octet of a -- UTF-8 [RFC2279] string } 4.3.2. Tokens from GSS_GetMIC and GSS_Wrap RFC 2078 defines the token emitted by GSS_GetMIC and GSS_Wrap as: PerMsgToken ::= -- as emitted by GSS_GetMIC and processed by GSS_VerifyMIC -- ASN.1 structure not required innerMsgToken ANY Expires: December 1999 [Page 13]
INTERNET-DRAFT LIPKEY June 1999 SealedMessage ::= -- as emitted by GSS_Wrap and processed by GSS_Unwrap -- includes internal, mechanism-defined indicator -- of whether or not encrypted -- ASN.1 structure not required sealedUserData ANY As one can see, there are no mechanism independent prefixes in PerMSGToken or SealedMessage, and no explicit mechanism specific information either. Since LIPKEY doesn't add any value to GSS_GetMIC and GSS_Wrap other than passing the message to the SPKM-3 GSS_GetMIC and GSS_Wrap, LIPKEY's PerMsgToken and SealedMessage tokens are exactly what SPKM-3's GSS_GetMIC and GSS_Wrap routines produce. 4.4. Quality of Protection LIPKEY, being a pass through for GSS_Wrap and GSS_GetMIC to SPKM-3, doesn't interpret or alter the QOPs passed to the aforementioned routines or received from their complements, GSS_Unwrap, and GSS_VerifyMIC. This LIPKEY supports the same set of QOPs as SPKM-3. The SPKM-3 initiator and target negotiate the set of algorithms they mutually support, using the procedure defined in Section 5.2 of RFC 2025. If a QOP of zero is specified, then the initiator and target will use the first C-ALG (privacy), and I-ALG integrity algorithm negotiated. SPKM breaks the QOP into several fields, as reproduced here from Section 5.2 of RFC 2025: Confidentiality Integrity 31 (MSB) 16 15 (LSB) 0 -------------------------------|------------------------------- | TS(5) | U(3) | IA(4) | MA(4) | TS(5) | U(3) | IA(4) | MA(4) | -------------------------------|------------------------------- The MA subfields enumerate mechanism-defined algorithms. Since this memorandum introduces a new mechanism, SPKM-3, within the SPKM family, it is appropriate to add the triple DES algorithm in the MA subfield of the Confidentiality field. The complete set of Confidentiality MA algorithms is thus: 0001 (1) = DES-CBC 0010 (2) = DES-EDE3-CBC Where "0001" and "0010" are in base 2. Adding support for DES-EDE3- CBC in the above manner to SPKM-1 and SPKM-2 does not impair SPKM-1 and SPKM-2 backward compatibility because, as noted previously, SPKM Expires: December 1999 [Page 14]
INTERNET-DRAFT LIPKEY June 1999 negotiates algorithms. An older SPKM-1 or SPKM-2 that doesn't recognize DES-EDE3-CBC won't select it. 5. Security Considerations 5.1. Password Management LIPKEY sends the clear text password encrypted by triple DES, so the risk in this approach is in how the target manages the password after it is done with it. The approach should be safe, provided the target clears the memory (primary and secondary, such as disk) buffers that contained the password, and any hash of the password immediately after it has verified the user's password. 5.2. Certificate Authorities The initiator must have a list of trusted Certificate Authorities in order to verify the checksum on the SPKM-3 target's context reply token. If it encounters a certificate signed by an unknown and/or untrusted certificate authority, the initiator MUST NOT silently accept the certificate. If it does wish to accept the certificate, it MUST get confirmation from the user running the application that is using GSS-API. Expires: December 1999 [Page 15]
INTERNET-DRAFT LIPKEY June 1999 References [CCITT] CCITT (1988). "Recommendation X.208: Specification of Abstract Syntax Notation One (ASN.1)" [EFF] Electronic Frontier Foundation, John Gilmore (Editor), (1998). "Cracking Des: Secrets of Encryption Research, Wiretap Politics & Chip Design". O'Reilly & Associates, ISBN 1565925203. [PKCS-3] RSA Laboratories (1993). "PKCS #3: Diffie-Hellman Key- Agreement Standard, Version 1.4," ftp://ftp.rsa.com/pub/pkcs/ascii/pkcs-3.asc [RSA] S/MIME Editor, RSA Data Security, Inc. (1995). "S/MIME Implementation Guide Interoperability Profile, Version 1." ftp://ftp.rsa.com/pub/S-MIME/smimeimp.txt [Sandberg] Sandberg, R., Goldberg, D., Kleiman, S., Walsh, D., Lyon, B.. (1985). "Design and Implementation of the Sun Network Filesystem," Proceedings of the 1985 Summer USENIX Technical Conference. [RFC1831] Srinivasan, R. (1995). "RPC: Remote Procedure Call Protocol Specification Version 2," RFC 1831. http://info.internet.isi.edu/in-notes/rfc/files/rfc1831.txt [RFC1832] Srinivasan, R. (1995). "XDR: External Data Representation Standard," RFC 1832. http://info.internet.isi.edu/in-notes/rfc/files/rfc1832.txt [RFC2203] Eisler, M., Chiu, A., Ling L. (1997). "RPCSEC_GSS Protocol Specification," RFC 2203. http://info.internet.isi.edu/in-notes/rfc/files/rfc2203.txt [RFC2025] Adams, C. (1996). "The Simple Public-Key GSS-API Mechanism (SPKM)," RFC 2025. http://info.internet.isi.edu/in-notes/rfc/files/rfc2025.txt [RFC2078] Linn, J. (1997). "Generic Security Service Application Program Interface, Version 2," RFC 2078. http://info.internet.isi.edu/in-notes/rfc/files/rfc2078.txt Expires: December 1999 [Page 16]
INTERNET-DRAFT LIPKEY June 1999 [RFC2119] Bradner, S. (1997). "Key words for use in RFCs to Indicate Requirement Levels," RFC 2119. http://info.internet.isi.edu/in-notes/rfc/files/rfc2119.txt [RFC2246] T. Dierks, C. Allen (1999). "The TLS Protocols Version 1.0," RFC 2246. http://info.internet.isi.edu/in-notes/rfc/files/rfc2246.txt [RFC2279] Yergeau, F. (1998), "UTF-8, a transformation format of ISO 10646", RFC2279, http://info.internet.isi.edu/in-notes/rfc/files/rfc2279.txt [X9.52] American National Standards Institute (1996) ANSI Draft X9.52. "Triple Data Encryption Algorithms Modes of Operations," Revision 6.0. Acknowledgments The author thanks and acknowledges: * Jack Kabat for his patient explanation of the intricacies of SPKM, his excellent suggestions, and review comments. * Denis Pinkas for his review comments. * This memorandum includes ASN.1 definitions for GSS-API tokens from RFC 2078, which was authored by John Linn. * This memorandum includes ASN.1 definitions and other text from the SPKM definition in RFC 2025, which was authored by Carlisle Adams. Author's Address Address comments related to this memorandum to: cat-ietf@mit.edu Mike Eisler Sun Microsystems, Inc. 5565 Wilson Road Colorado Springs, CO 80919 Phone: 1-719-599-9026 E-mail: mre@eng.sun.com Expires: December 1999 [Page 17]
