Internet-Draft Tom Arnold (CyberSource) Category: Application Jason Eaton (CyberSource) March 19, 1999 Michael Jimenez (CyberSource) Expires in six months Hubert Chen (CyberSource) Simple Commerce Messaging Protocol (SCMP) (draft-arnold-scmp-02.txt) Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. This document is an Internet-Draft. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and 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. 1. Introduction The Simple Commerce Messaging Protocol (SCMP) is a general-purpose commerce transport protocol for secure, real-time communication of a set of data from a sending agent's application to a receiving agent's server. Additionally the response by the receiving agent's sever to the sending agent is the reply from the request represented by the set of data in the message's payload. The intent of this protocol is to define a method where trading partners can perform on-line business requests in an environment where the sending partner is fully authenticated, and the message cannot be repudiated. The taxonomy of the SCMP message payload is not in the scope of this document. The SCMP protocol does not specify payload definitions or how trading partners are expected to process the payload, beyond basic server-level functions related to processing SCMP headers. This intent is to permit trading partners the flexibility to implement either a standard commerce message format as in ANSI-X12 Electronic Data Interchange (EDI) or some other non-standard payload format. The only requirement on the message payload is that it be identified to the receiver utilizing MIME naming and formatting [MIME] and is used to identify the type of payload contained in the SCMP data area. In this manner, SCMP fundamentally differs from many emerging commerce message protocols. Beyond specifying the method for encryption, authentication and handling, these other protocols specify the contents of the message and details how a server is to process and respond to a given message payload. 1.1. Document Overview This document describes SCMP from the standpoint of how trading partners would implement a client/server request processing system via an untrusted network connection. In a on-line, electronic commerce environment, trading partners require a scalable, message handling system that will meet these minimum requirements: 1.1.1 Real-time Request and Response A single message containing all credential and payload data is prepared by a sending agent and sent to a receiving agent. The receiving agent, upon verification of sender's credentials, MUST process the payload, format a reply, and respond to the sender as the response to the inbound connection. 1.1.2 Message Privacy Through use of cryptographic methods, the privacy of the sender's message payload MUST be assured should a message payload be intercepted. 1.1.2 Message Integrity If a message arrives in an incomplete or tampered condition from a sending agent, the receiving agent's server MUST detect the condition, deny message payload processing, and respond with an appropriate error message. 1.1.3 Authentication of Sending and Receiving Agents Messages between trading partners, as represented by sending and receiving agents, MUST contain attributes that assure a given request could only be from a specific trading partner. 1.1.4 Non-repudiation When a receiving agent's server receives a request to process a payload, the receiving agent's application SHOULD guarantee that the sender cannot, at some later time, refute having sent the request. Non-repudiation is defined as, the inability of either trading partner (sender or receiver) to refute the sending of an SCMP request or SCMP reply. An Electronic Commerce provider will typically provide financial based functionality such as authorization, settlement, and crediting, of credit card accounts and/or merchant accounts. This functionality requires that the Electronic Commerce Provider execute financial transactions on behalf of the merchant, or trading partner. Therefore it is desirable that the transaction directives which are given in an SCMP message are non-refutable. 1.1.5 Payload Independence The messaging system MUST perform consistently for all payload formats. 1.1.6 Standards Based The messaging protocol MUST be based on proven, existing cryptography and Internet standards. 1.1.7 Use of Standard Credentials Standard credential formats MUST be used to maximize interoperability of common Public Key Infrastructures. 1.1.8 Transport Independent The message MUST be transportable over the most common Internet transport protocols. 1.1.9 Service Level Guarantee The receiving agent MUST guarantee a response within the time designated by the sender, or reject the message with an appropriate error message. 1.1.10 State Independence There MUST be no state dependency by either a sender's or receiver's application on the messaging protocol. 1.2. Terminology Throughout this draft, the terms MUST, MUST NOT, SHOULD, and SHOULD NOT are used in conformance to the definitions in [MUSTSHOULD]. 1.3. Definitions Several terms will be used when specifying SCMP. Trading Partners Two entities wishing to perform some on-line request processing where authentication, privacy, integrity and non-repudiation of the requests are important. Trading partners have established a trusted relationship between each other. Client An application program that executes on a remote system, used by a trading partner to request services from a server via an untrusted or publicly switched packet network, like the Internet. Server An application program used to process SCMP messages received from a client, and generate appropriate replies which are sent back to the client. Sending Agent An entity that operates or uses a Client for requesting on-line services from a server. Receiving Agent An entity that operates a Server, receives and processes requests from a plurality of Clients. Request A discrete unit of service embodied in a single SCMP message/reply pair. Payload The meaningful content provided by a client to a server, encapsulated in an SCMP message. Similarly the meaningful content provided by a server to a client, encapsulated in an SCMP message. Message An interchangeable term used to mean a Request. Reply An SCMP message sent from a server to a client. Services Algorithms implemented by the server application which are executed as designated by the payload. Each available algorithm is a service. 2. Payload Encapsulation The payload of an SCMP message MUST be prepared as a standard MIME entity as defined in the [MIME] specification. The [SMIME] document describes how the resulting MIME entity SHOULD be cryptographically enhanced according to [PKCS-7]. An SCMP compliant server SHOULD implement the three message types as described in [SMIME], signed, enveloped, and signed/enveloped. A SCMP compliant server MUST implement signed/envelope message type as described in [SMIME]. It is recommended, for non-repudiation concerns that the trading partners SHOULD exchange signed or signed/enveloped SCMP message types. It is also recommended that strong enough cryptographic methods be used to insure authenticity, integrity, non-repudiation, and privacy of the payload. But, if the trading partners form a private agreement, clear data or signed-only data MAY be exchanged. However, an SCMP compliant server MUST support encryption even if encryption is not being used. In addition to the standard MIME headers, a compliant implementation MUST define "SCMP-protocol-version" and "SCMP-sender-name". These headers added to the outer MIME entity, as described in [SMIME]. Use of the remaining standard SMIME (outside MIME entity) headers are assumed. This includes any additional implementation-specific headers. These headers will most likely be ones that need to be processed prior to payload decryption. 2.1 SCMP Protocol Version The SCMP-protocol-version header is used to designate the SCMP protocol version. Server implementations MAY reject the request based upon protocol version, before any message processing occurs. An example SCMP-protocol-version header will be in this format: SCMP-protocol-version: v2.0 The possible protocol versions MUST be agreed upon by the trading partners. 2.2 SCMP Sender Name The SCMP-sender-name header is used to designate the SCMP sender name. Thereby the sender name can be accessed before any decryption of the request is performed. Server implementations MAY reject the request based upon sender name, before any message processing occurs. An SCMP-sender-name header will be in this format: SCMP-sender-name: CyberSource The possible sender names MUST be agreed upon by the trading partners. 3. SCMP Payload-based Headers This section describes the payload-based extensions that MUST be implemented by both the client and server to insure correct and proper request processing. Setting the SCMP service headers is the responsibility of the sending agent's client application. Processing the SCMP payload headers is the responsibility of the receiving agent's server application processing the request. The following headers are described for the payload of the S/MIME entity, and MUST be prepared as defined in [MIME]. Thus if the S/MIME message type is signed/enveloped ( which is recommended ), then the SCMP headers will be encrypted with the sender's message payload. 3.1. Request Time to Live This describes the amount of actual processing time in seconds the client expects the server to complete payload processing prior to responding with an appropriate reply. An SCMP server receiving a SCMP message MUST evaluate the request time to live value and determine if it can execute the required service(s) in the amount of time designated. Assuming the server believes it can complete the work within the allowed time, it will accept the request. If not, the server MUST return an error to the client stating it could not accept the request. Once a server has accepted a request, it MUST process it until the time to live value has been reached or until completion. If the time to live value is reached during execution, the server MUST return an error to the client stating that a time-out has occurred. Application functions to insure data consistency, integrity, or rollback after the time to live value has been exceeded will be the responsibility of the server application. A policy on what application actions a server will take upon exceeding a time to live value SHOULD be published by the receiving agent operating the server. An example of a policy in this are would be one where a receiving agent's server will continue processing the request after a request time to live value has been exceeded. Given this policy, a client, having received a time-out error message, would send a "request status message" to the server, referencing the original scmp-request-id (from the message that timed out) in the message payload. The server's reply to this status message would be the reply that would have been sent had the processing time not exceeded the time to live metric. The time to live header will be in this format: SCMP-request-time-to-live: 0..n (seconds) 3.2. Message Type This value specifies the type of payload that is contained in the SCMP message. The intent of this header is to provide a meta-level description of the message payload and allow a receiving server to decide which services or associated algorithms to use in processing the payload. Message type is specified as follows: SCMP-message-type: [service-name]/[version-number] The assignment of service names MUST be provided by the server to a client at the time a service is published. For instance, if a service was published called "CommerceService", the SCMP-message-type might be represented as: SCMP-message-type: CommerceService/1.0 It is assumed that trading partners will agree on service names before requests are processed. 3.3. Request ID A value in the format described in  that identifies a specific instance of a request. Request ID's MUST be generated by the client application, thus assuring that the scmp-request-id is available in the event that the request cannot be sent to the server due to errors. An example of a request scmp-request-id is: scmp-request-id: 0917293049096167904518 The scmp-request-id MUST be unique in the domain of a client application and SHOULD NOT be easy to predict so as to prevent a potential replay attack. A client application, when preparing the scmp-request-id, SHOULD perform a random number generation with sufficient degrees of randomness, to ensure unpredictability, and generate a client side time value, to ensure uniqueness of the result. These two data items together SHOULD form the resulting scmp-request-id. Servers MAY use a scmp-request-id as a reference and handle to the original request during server message processing. 4. SCMP Data Block (Message Payload) The payload or data block can be any arbitrary data type in the format as specified by the SCMP-message-type. This payload forms the content of the SMIME message as described in [SMIME]. 5. Certificates Every trading partner implementing SCMP MUST exchange certificates that have been issued and signed by one or more mutually trusted certificate authorities. Prior to establishing trading partner relationships, the sender and receiver MUST acquire mutually acceptable public root certificates from the agreed upon certificate authority or authorities. Trading partners, upon receiving or exchanging public key certificates for the first time, SHOULD validate the certificate and certificate chain before processing an SCMP request. Prior to performing any application functions on a SCMP request payload, the receiving agent's server MUST verify that the request has been made by an authorized sender and that the sender's certificate has not been revoked. A server certificate revalidation policy, related to the frequency certificates are revalidated against a certificate authority's certificate revocation list, is not specified by SCMP. This matter is left as a policy decision for the operator of the SCMP server. 6. Transport Implementations SCMP can be implemented using any variety of transport methods as agreed between trading partners. Here are a few examples. http: This delivers a SCMP message to a server URL and should use a POST function. electronic mail: This will support a queued batch processing service 7. Receiving Server Functions This section describes minimal server functions required to implement SCMP. 7.1. General A SCMP server receives a message from a client, processes the message and generates a reply. If the message type is signed or signed/enveloped the server initially validates the outer signature. If the outer signature is not valid the server MUST NOT process the request further. 7.1.1. Message Timestamp The time a request was sent SHOULD be derived from the standard SMIME date header. Clients and servers SHOULD be synchronized using [NTP] or Secure NTP. The sender of an SCMP message MUST place the time a message was dispatched into the SMIME header in [MIME] format. The message timestamp SHOULD be used, in combination with the scmp-request-id, by the server to aid in detection of a potential replay attack. It is recommended that servers SHOULD run a client-visible NTP server to allow SCMP client applications to synchronize clocks as required. 7.1.2 Support for Request Non-Repudiation Support for non-repudiation SHOULD be included in any complete SCMP implementation, as described in the following subsections. If the message is of signed or signed/enveloped type, the receiving agent's server MUST implement support for non-repudiation. 184.108.40.206 Establish Trusted Trading Relationship Prior to exchanging messages, sending and receiving agents MUST exchange public key certificates. 220.127.116.11 Client Private Key Storage The sending agent, maintaining a SCMP client application, MUST maintain the private key in a secure location. Should a sending agent loose control of their private key, they MUST notify the receiving agent at the earliest possible time. 18.104.22.168 Client Message Signing The client application signs SCMP messages using their private key as described in [SMIME]. 22.214.171.124 Server Processing The receiving agent's server application evaluates the digital signature, thereby guaranteeing that the message payload has not been altered in transit, and that the message was, in fact, signed by a specific trading partner (client) who possess the proper credentials. 126.96.36.199 Server Accounting The receiving agent's server application MUST store the original signed/ encrypted message in an unprocessed state along with the timestamp for identifying when the message was received. As the server processes the sending agent's message, a record describing the processing steps along with the appropriate timestamp MUST be appended to a accounting log for the sending agent's request. 188.8.131.52 Revokation All messages signed by a sending agent's client application in accordance with [SMIME] and sent to a receiving agent's server SHALL be considered non-repudiable. Repudiation occurs when the sending agent notifies the receiving agent that the sending agent's public key certificate is revoked. The timestamp of this revokation event MUST be the current time at the receiving agent's server. Should a receiving agent's server receive a request after being notified that the public key certificate used to evaluate the sending agent's digital signature has been revoked, this request MUST be considered invalid. 7.2. Application issues The server MUST evaluate the signature of the message, if the message is of signed or signed/enveloped type, prior to processing the message payload. Within this process the server SHOULD obtain the senders certificate via the distinguished name in the certificate as described in [SMIME]. In performing this authentication process, the server MUST validate the senders certificate and verify that the sender's certificate is not listed in any available revocation systems. Assuming the SCMP message's signature is valid, the server will process requests with the appropriate service designated by the SCMP-message-type value. 7.2.1. Request Serialization A server MAY NOT guarantee serialized request processing. If requests must be serialized, it is expected that all of the serialized transactions will be received in a single message payload or that other content specific serialization systems will be used. 7.2.2. Server Errors A server may encounter several classes of error conditions. The server MUST be capable of reporting an error as described in section 8 of this document. Error Detection may vary based on specific implementation. A server MUST be capable of detecting a duplicate scmp-request-id and reply to the sending client application with the reply of the original request. Duplicate request detection MUST be based on the scmp-request-id and the distinguished name of the signer to prevent denial of service attacks. In the event of a duplicate request being detected the server MUST: 1) lookup the prior request 2) verify the sender is the same 3) return an appropriate error message to the client. In the event that the three above steps fail, the server MUST return an appropriate SCMP error message. 8. Protocol Level Error Messages In general SCMP does not concern itself with application level errors. Such errors MUST be returned in an SCMP reply with appropriate application specific formatting. 8.1. Format SCMP error messages are returned by a server as signed data. SCMP errors MUST NOT be encrypted to permit clients to process encryption related errors. The format of SCMP errors is: SCMP <error number> <error message text> 8.2. Client Application Error Handling Client action in the case of error return is error specific and not defined. If the server fails to return any reply within twice the time to live requested (due to unspecified server or network failure) the client SHOULD re-send the request. Upon receipt of a duplicate request the server will respond as described in 7.2.2. Clients MUST NOT retry a request in an interval which is less than the time to live value of the original request. 9. Author's Address Tom Arnold CyberSource Corporation 550 S. Winchester Blvd., #301 San Jose, CA 95128 E-mail: firstname.lastname@example.org Phone: 408-556-9100 Jason Eaton CyberSource Corporation 550 S. Winchester Blvd., #301 San Jose, CA 95128 E-mail: email@example.com Phone: 408-556-9100 Michael Jimenez CyberSource Corporation 550 S. Winchester Blvd., #301 San Jose, CA 95128 E-mail: firstname.lastname@example.org Phone: 408-556-9100 Hubert Chen CyberSource Corporation 550 S. Winchester Blvd., #301 San Jose, CA 95128 E-mail: email@example.com Phone: 408-556-9100 10. Acknowledgements The authors wish to recognize and thank several individuals (listed in alphabetic order) who have and continue to support the development of requirements and improvement of this protocol. Mike Agostino (Vulcan), Ron Bose (LitleNet), David Burdett (Mondex), Leonard Cantor (IBM), Dan Corcoran (Equifax), Steve Crocker (Crocker Assoc.), Tony Curwen (Ingram Micro), Donald Eastlake (IBM), Richard Frank (Intertrust), James Gavin (Commercenet), Paul Guthrie (VISA International), Bengamin Hipp (FUSA/Paymentech), Andy Jeffrey (Sonnet Financial), Helle Jespersen (IBM), "Sean Kiewiet" <firstname.lastname@example.org>, Connie Lindgreen (IBM), Michael Myers (VeriSign), Allan Ottosen (PBS), John Pettitt (Beyond.com), Jesse Rendleman (CyberSource), Don Sloan (Tech Data), Carl Stucke (Equifax), Frank Tyksen (Portland Software), Huy Vu (VISA USA), Sean Youssefi (CobWeb) 11. References  D. Crocker, "Standard for the format of ARPA Internet text messages." RFC 0822, IETF, Aug. 1982. [SMIME] S. Dusse, et. al, "S/MIME Version 2 Message Specification", RFC 2311, IETF, March 1998. [MIME] "MIME Part1: Format of Internet Message Bodies", RFC 2045; "MIME Part2: Media Types", RFC 2046; "MIME Part 3: Message Header Extensions for Non-ASCII Text", RFC 2047; "MIME Part 4: Registration Procedures", RFC 2048; "MIME Part 5: Conformance Criteria and Examples", RFC 2049, IETF. [MUSTSHOULD] "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, IETF. [NTP] D. Mills. "Network Time Protocol", RFC 1119, IETF, September 1989. [PKCS-7] B. Kaliski, "PKCS #7: Cryptograpic Message Syntax" RFC 2315, IETF, March 1998.