GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


rfc:rfc1057

Network Working Group Sun Microsystems, Inc. Request For Comments: 1057 June 1988 Obsoletes: RFC 1050

                     RPC: Remote Procedure Call
                       Protocol Specification
                             Version 2

STATUS OF THIS MEMO

 This RFC describes a standard that Sun Microsystems and others are
 using, and is one we wish to propose for the Internet's
 consideration.  This memo is not an Internet standard at this time.
 Distribution of this memo is unlimited.

1. INTRODUCTION

 This document specifies version two of the message protocol used in
 Sun's Remote Procedure Call (RPC) package.  The message protocol is
 specified with the eXternal Data Representation (XDR) language [9].
 This document assumes that the reader is familiar with XDR.  It does
 not attempt to justify remote procedure calls systems or describe
 their use.  The paper by Birrell and Nelson [1] is recommended as an
 excellent background for the remote procedure call concept.

2. TERMINOLOGY

 This document discusses clients, calls, servers, replies, services,
 programs, procedures, and versions.  Each remote procedure call has
 two sides: an active client side that sends the call to a server,
 which sends back a reply.  A network service is a collection of one
 or more remote programs.  A remote program implements one or more
 remote procedures; the procedures, their parameters, and results are
 documented in the specific program's protocol specification (see
 Appendix A for an example).  A server may support more than one
 version of a remote program in order to be compatible with changing
 protocols.
 For example, a network file service may be composed of two programs.
 One program may deal with high-level applications such as file system
 access control and locking.  The other may deal with low-level file
 input and output and have procedures like "read" and "write".  A
 client of the network file service would call the procedures
 associated with the two programs of the service on behalf of the
 client.
 The terms client and server only apply to a particular transaction; a

Sun Microsystems [Page 1] RFC 1057 Remote Procedure Call, Version 2 June 1988

 particular hardware entity (host) or software entity (process or
 program) could operate in both roles at different times.  For
 example, a program that supplies remote execution service could also
 be a client of a network file service.  On the other hand, it may
 simplify software to separate client and server functionality into
 separate libraries or programs.

3. THE RPC MODEL

 The Sun RPC protocol is based on the remote procedure call model,
 which is similar to the local procedure call model.  In the local
 case, the caller places arguments to a procedure in some well-
 specified location (such as a register window).  It then transfers
 control to the procedure, and eventually regains control.  At that
 point, the results of the procedure are extracted from the well-
 specified location, and the caller continues execution.
 The remote procedure call model is similar.  One thread of control
 logically winds through two processes: the caller's process, and a
 server's process.  The caller process first sends a call message to
 the server process and waits (blocks) for a reply message.  The call
 message includes the procedure's parameters, and the reply message
 includes the procedure's results.  Once the reply message is
 received, the results of the procedure are extracted, and caller's
 execution is resumed.
 On the server side, a process is dormant awaiting the arrival of a
 call message.  When one arrives, the server process extracts the
 procedure's parameters, computes the results, sends a reply message,
 and then awaits the next call message.
 In this model, only one of the two processes is active at any given
 time.  However, this model is only given as an example.  The Sun RPC
 protocol makes no restrictions on the concurrency model implemented,
 and others are possible.  For example, an implementation may choose
 to have RPC calls be asynchronous, so that the client may do useful
 work while waiting for the reply from the server.  Another
 possibility is to have the server create a separate task to process
 an incoming call, so that the original server can be free to receive
 other requests.
 There are a few important ways in which remote procedure calls differ
 from local procedure calls:
 1. Error handling: failures of the remote server or network must be
 handled when using remote procedure calls.
 2. Global variables and side-effects: since the server does not have

Sun Microsystems [Page 2] RFC 1057 Remote Procedure Call, Version 2 June 1988

 access to the client's address space, hidden arguments cannot be
 passed as global variables or returned as side effects.
 3. Performance:  remote procedures usually operate one or more orders
 of magnitude slower than local procedure calls.
 4. Authentication: since remote procedure calls can be transported
 over insecure networks, authentication may be necessary.
 The conclusion is that even though there are tools to automatically
 generate client and server libraries for a given service, protocols
 must still be designed carefully.

4. TRANSPORTS AND SEMANTICS

 The RPC protocol can be implemented on several different transport
 protocols.  The RPC protocol does not care how a message is passed
 from one process to another, but only with specification and
 interpretation of messages.  On the other hand, the application may
 wish to obtain information about (and perhaps control over) the
 transport layer through an interface not specified in this document.
 For example, the transport protocol may impose a restriction on the
 maximum size of RPC messages, or it may be stream-oriented like TCP
 with no size limit.  The client and server must agree on their
 transport protocol choices, through a mechanism such as the one
 described in Appendix A.
 It is important to point out that RPC does not try to implement any
 kind of reliability and that the application may need to be aware of
 the type of transport protocol underneath RPC.  If it knows it is
 running on top of a reliable transport such as TCP [6], then most of
 the work is already done for it.  On the other hand, if it is running
 on top of an unreliable transport such as UDP [7], it must implement
 its own time-out, retransmission, and duplicate detection policies as
 the RPC layer does not provide these services.
 Because of transport independence, the RPC protocol does not attach
 specific semantics to the remote procedures or their execution
 requirements.  Semantics can be inferred from (but should be
 explicitly specified by) the underlying transport protocol.  For
 example, consider RPC running on top of an unreliable transport such
 as UDP.  If an application retransmits RPC call messages after time-
 outs, and does not receive a reply, it cannot infer anything about
 the number of times the procedure was executed.  If it does receive a
 reply, then it can infer that the procedure was executed at least
 once.
 A server may wish to remember previously granted requests from a

Sun Microsystems [Page 3] RFC 1057 Remote Procedure Call, Version 2 June 1988

 client and not regrant them in order to insure some degree of
 execute-at-most-once semantics.  A server can do this by taking
 advantage of the transaction ID that is packaged with every RPC
 message.  The main use of this transaction is by the client RPC layer
 in matching replies to calls.  However, a client application may
 choose to reuse its previous transaction ID when retransmitting a
 call.  The server may choose to remember this ID after executing a
 call and not execute calls with the same ID in order to achieve some
 degree of execute-at-most-once semantics.  The server is not allowed
 to examine this ID in any other way except as a test for equality.
 On the other hand, if using a "reliable" transport such as TCP, the
 application can infer from a reply message that the procedure was
 executed exactly once, but if it receives no reply message, it cannot
 assume the remote procedure was not executed.  Note that even if a
 connection-oriented protocol like TCP is used, an application still
 needs time-outs and reconnection to handle server crashes.
 There are other possibilities for transports besides datagram- or
 connection-oriented protocols.  For example, a request-reply protocol
 such as VMTP [2] is perhaps a natural transport for RPC.  The Sun RPC
 package currently uses both TCP and UDP transport protocols, with
 experimentation underway on others such as ISO TP4 and TP0.

5. BINDING AND RENDEZVOUS INDEPENDENCE

 The act of binding a particular client to a particular service and
 transport parameters is NOT part of this RPC protocol specification.
 This important and necessary function is left up to some higher-level
 software.  (The software may use RPC itself; see Appendix A.)
 Implementors could think of the RPC protocol as the jump-subroutine
 instruction ("JSR") of a network; the loader (binder) makes JSR
 useful, and the loader itself uses JSR to accomplish its task.
 Likewise, the binding software makes RPC useful, possibly using RPC
 to accomplish this task.

6. AUTHENTICATION

 The RPC protocol provides the fields necessary for a client to
 identify itself to a service, and vice-versa, in each call and reply
 message.  Security and access control mechanisms can be built on top
 of this message authentication.  Several different authentication
 protocols can be supported.  A field in the RPC header indicates
 which protocol is being used. More information on specific
 authentication protocols is in section 9: "Authentication Protocols".

Sun Microsystems [Page 4] RFC 1057 Remote Procedure Call, Version 2 June 1988

7. RPC PROTOCOL REQUIREMENTS

 The RPC protocol must provide for the following:
 (1) Unique specification of a procedure to be called.
 (2) Provisions for matching response messages to request messages.
 (3) Provisions for authenticating the caller to service and vice-
     versa.
 Besides these requirements, features that detect the following are
 worth supporting because of protocol roll-over errors, implementation
 bugs, user error, and network administration:
 (1) RPC protocol mismatches.
 (2) Remote program protocol version mismatches.
 (3) Protocol errors (such as misspecification of a procedure's
     parameters).
 (4) Reasons why remote authentication failed.
 (5) Any other reasons why the desired procedure was not called.

7.1 RPC Programs and Procedures

 The RPC call message has three unsigned integer fields -- remote
 program number, remote program version number, and remote procedure
 number -- which uniquely identify the procedure to be called.
 Program numbers are administered by some central authority (like
 Sun).  Once implementors have a program number, they can implement
 their remote program; the first implementation would most likely have
 the version number 1.  Because most new protocols evolve, a version
 field of the call message identifies which version of the protocol
 the caller is using.  Version numbers make speaking old and new
 protocols through the same server process possible.
 The procedure number identifies the procedure to be called.  These
 numbers are documented in the specific program's protocol
 specification.  For example, a file service's protocol specification
 may state that its procedure number 5 is "read" and procedure number
 12 is "write".
 Just as remote program protocols may change over several versions,
 the actual RPC message protocol could also change.  Therefore, the
 call message also has in it the RPC version number, which is always
 equal to two for the version of RPC described here.
 The reply message to a request message has enough information to
 distinguish the following error conditions:
 (1) The remote implementation of RPC does not speak protocol version

Sun Microsystems [Page 5] RFC 1057 Remote Procedure Call, Version 2 June 1988

 2. The lowest and highest supported RPC version numbers are returned.
 (2) The remote program is not available on the remote system.
 (3) The remote program does not support the requested version number.
 The lowest and highest supported remote program version numbers are
 returned.
 (4) The requested procedure number does not exist.  (This is usually
 a client side protocol or programming error.)
 (5) The parameters to the remote procedure appear to be garbage from
 the server's point of view.  (Again, this is usually caused by a
 disagreement about the protocol between client and service.)

7.2 Authentication

 Provisions for authentication of caller to service and vice-versa are
 provided as a part of the RPC protocol.  The call message has two
 authentication fields, the credentials and verifier.  The reply
 message has one authentication field, the response verifier.  The RPC
 protocol specification defines all three fields to be the following
 opaque type (in the eXternal Data Representation (XDR) language [9]):
       enum auth_flavor {
          AUTH_NULL       = 0,
          AUTH_UNIX       = 1,
          AUTH_SHORT      = 2,
          AUTH_DES        = 3
          /* and more to be defined */
       };
       struct opaque_auth {
          auth_flavor flavor;
          opaque body<400>;
       };
 In other words, any "opaque_auth" structure is an "auth_flavor"
 enumeration followed by bytes which are opaque to (uninterpreted by)
 the RPC protocol implementation.
 The interpretation and semantics of the data contained within the
 authentication fields is specified by individual, independent
 authentication protocol specifications.  (Section 9 defines the
 various authentication protocols.)
 If authentication parameters were rejected, the reply message
 contains information stating why they were rejected.

Sun Microsystems [Page 6] RFC 1057 Remote Procedure Call, Version 2 June 1988

7.3 Program Number Assignment

 Program numbers are given out in groups of hexadecimal 20000000
 (decimal 536870912) according to the following chart:
               0 - 1fffffff   defined by Sun
        20000000 - 3fffffff   defined by user
        40000000 - 5fffffff   transient
        60000000 - 7fffffff   reserved
        80000000 - 9fffffff   reserved
        a0000000 - bfffffff   reserved
        c0000000 - dfffffff   reserved
        e0000000 - ffffffff   reserved
 The first group is a range of numbers administered by Sun
 Microsystems and should be identical for all sites.  The second range
 is for applications peculiar to a particular site.  This range is
 intended primarily for debugging new programs.  When a site develops
 an application that might be of general interest, that application
 should be given an assigned number in the first range.  The third
 group is for applications that generate program numbers dynamically.
 The final groups are reserved for future use, and should not be used.

7.4 Other Uses of the RPC Protocol

 The intended use of this protocol is for calling remote procedures.
 Normally, each call message is matched with a reply message.
 However, the protocol itself is a message-passing protocol with which
 other (non-procedure call) protocols can be implemented.  Sun
 currently uses, or perhaps abuses, the RPC message protocol for the
 batching (or pipelining) and broadcast remote procedure calls.

7.4.1 Batching

 Batching is useful when a client wishes to send an arbitrarily large
 sequence of call messages to a server.  Batching typically uses
 reliable byte stream protocols (like TCP) for its transport.  In the
 case of batching, the client never waits for a reply from the server,
 and the server does not send replies to batch calls.  A sequence of
 batch calls is usually terminated by a legitimate remote procedure
 call operation in order to flush the pipeline and get positive
 acknowledgement.

7.4.2 Broadcast Remote Procedure Calls

 In broadcast protocols, the client sends a broadcast call to the
 network and waits for numerous replies.  This requires the use of
 packet-based protocols (like UDP) as its transport protocol.  Servers

Sun Microsystems [Page 7] RFC 1057 Remote Procedure Call, Version 2 June 1988

 that support broadcast protocols only respond when the call is
 successfully processed, and are silent in the face of errors.
 Broadcast calls use the Port Mapper RPC service to achieve their
 semantics.  See Appendix A for more information.

8. THE RPC MESSAGE PROTOCOL

 This section defines the RPC message protocol in the XDR data
 description language [9].
       enum msg_type {
          CALL  = 0,
          REPLY = 1
       };
 A reply to a call message can take on two forms: The message was
 either accepted or rejected.
       enum reply_stat {
          MSG_ACCEPTED = 0,
          MSG_DENIED   = 1
       };
 Given that a call message was accepted, the following is the status
 of an attempt to call a remote procedure.
       enum accept_stat {
          SUCCESS       = 0, /* RPC executed successfully       */
          PROG_UNAVAIL  = 1, /* remote hasn't exported program  */
          PROG_MISMATCH = 2, /* remote can't support version #  */
          PROC_UNAVAIL  = 3, /* program can't support procedure */
          GARBAGE_ARGS  = 4  /* procedure can't decode params   */
       };
 Reasons why a call message was rejected:
       enum reject_stat {
          RPC_MISMATCH = 0, /* RPC version number != 2          */
          AUTH_ERROR = 1    /* remote can't authenticate caller */
       };

Sun Microsystems [Page 8] RFC 1057 Remote Procedure Call, Version 2 June 1988

 Why authentication failed:
       enum auth_stat {
          AUTH_BADCRED      = 1,  /* bad credentials (seal broken) */
          AUTH_REJECTEDCRED = 2,  /* client must begin new session */
          AUTH_BADVERF      = 3,  /* bad verifier (seal broken)    */
          AUTH_REJECTEDVERF = 4,  /* verifier expired or replayed  */
          AUTH_TOOWEAK      = 5   /* rejected for security reasons */
       };
 The RPC message:
 All messages start with a transaction identifier, xid, followed by a
 two-armed discriminated union.  The union's discriminant is a
 msg_type which switches to one of the two types of the message.  The
 xid of a REPLY message always matches that of the initiating CALL
 message.  NB: The xid field is only used for clients matching reply
 messages with call messages or for servers detecting retransmissions;
 the service side cannot treat this id as any type of sequence number.
       struct rpc_msg {
          unsigned int xid;
          union switch (msg_type mtype) {
          case CALL:
             call_body cbody;
          case REPLY:
             reply_body rbody;
          } body;
       };
 Body of an RPC call:
 In version 2 of the RPC protocol specification, rpcvers must be equal
 to 2.  The fields prog, vers, and proc specify the remote program,
 its version number, and the procedure within the remote program to be
 called.  After these fields are two authentication parameters:  cred
 (authentication credentials) and verf (authentication verifier).  The
 two authentication parameters are followed by the parameters to the
 remote procedure, which are specified by the specific program
 protocol.

Sun Microsystems [Page 9] RFC 1057 Remote Procedure Call, Version 2 June 1988

       struct call_body {
          unsigned int rpcvers;       /* must be equal to two (2) */
          unsigned int prog;
          unsigned int vers;
          unsigned int proc;
          opaque_auth cred;
          opaque_auth verf;
          /* procedure specific parameters start here */
       };
 Body of a reply to an RPC call:
       union reply_body switch (reply_stat stat) {
       case MSG_ACCEPTED:
          accepted_reply areply;
       case MSG_DENIED:
          rejected_reply rreply;
       } reply;
 Reply to an RPC call that was accepted by the server:
 There could be an error even though the call was accepted.  The first
 field is an authentication verifier that the server generates in
 order to validate itself to the client.  It is followed by a union
 whose discriminant is an enum accept_stat.  The SUCCESS arm of the
 union is protocol specific.  The PROG_UNAVAIL, PROC_UNAVAIL, and
 GARBAGE_ARGS arms of the union are void.  The PROG_MISMATCH arm
 specifies the lowest and highest version numbers of the remote
 program supported by the server.

Sun Microsystems [Page 10] RFC 1057 Remote Procedure Call, Version 2 June 1988

       struct accepted_reply {
          opaque_auth verf;
          union switch (accept_stat stat) {
          case SUCCESS:
             opaque results[0];
             /*
              * procedure-specific results start here
              */
           case PROG_MISMATCH:
              struct {
                 unsigned int low;
                 unsigned int high;
              } mismatch_info;
           default:
              /*
               * Void.  Cases include PROG_UNAVAIL, PROC_UNAVAIL,
               * and GARBAGE_ARGS.
               */
              void;
           } reply_data;
       };
 Reply to an RPC call that was rejected by the server:
 The call can be rejected for two reasons: either the server is not
 running a compatible version of the RPC protocol (RPC_MISMATCH), or
 the server refuses to authenticate the caller (AUTH_ERROR). In case
 of an RPC version mismatch, the server returns the lowest and highest
 supported RPC version numbers.  In case of refused authentication,
 failure status is returned.
       union rejected_reply switch (reject_stat stat) {
       case RPC_MISMATCH:
          struct {
             unsigned int low;
             unsigned int high;
          } mismatch_info;
       case AUTH_ERROR:
          auth_stat stat;
       };

Sun Microsystems [Page 11] RFC 1057 Remote Procedure Call, Version 2 June 1988

9. AUTHENTICATION PROTOCOLS

 As previously stated, authentication parameters are opaque, but
 open-ended to the rest of the RPC protocol.  This section defines
 some "flavors" of authentication implemented at (and supported by)
 Sun.  Other sites are free to invent new authentication types, with
 the same rules of flavor number assignment as there is for program
 number assignment.

9.1 Null Authentication

 Often calls must be made where the client does not know its identity
 or the server does not care who the client is.  In this case, the
 flavor value (the discriminant of the opaque_auth's union) of the RPC
 message's credentials, verifier, and reply verifier is "AUTH_NULL".
 The bytes of the opaque_auth's body are undefined.  It is recommended
 that the opaque length be zero.

9.2 UNIX Authentication

 The client may wish to identify itself as it is identified on a
 UNIX(tm) system.  The value of the credential's discriminant of an
 RPC call message is "AUTH_UNIX".  The bytes of the credential's
 opaque body encode the the following structure:
       struct auth_unix {
          unsigned int stamp;
          string machinename<255>;
          unsigned int uid;
          unsigned int gid;
          unsigned int gids<16>;
       };
 The "stamp" is an arbitrary ID which the caller machine may generate.
 The "machinename" is the name of the caller's machine (like
 "krypton").  The "uid" is the caller's effective user ID.  The "gid"
 is the caller's effective group ID.  The "gids" is a counted array of
 groups which contain the caller as a member.  The verifier
 accompanying the credentials should be of "AUTH_NULL" (defined
 above).  Note these credentials are only unique within a particular
 domain of machine names, uids, and gids.  Inter-domain naming is
 beyond the scope of this document.
 The value of the discriminant of the reply verifier received in the
 reply message from the server may be "AUTH_NULL" or "AUTH_SHORT".  In
 the case of "AUTH_SHORT", the bytes of the reply verifier's string
 encode an opaque structure.  This new opaque structure may now be
 passed to the server instead of the original "AUTH_UNIX" flavor

Sun Microsystems [Page 12] RFC 1057 Remote Procedure Call, Version 2 June 1988

 credentials.  The server may keep a cache which maps shorthand opaque
 structures (passed back by way of an "AUTH_SHORT" style reply
 verifier) to the original credentials of the caller.  The caller can
 save network bandwidth and server cpu cycles by using the new
 credentials.
 The server may flush the shorthand opaque structure at any time.  If
 this happens, the remote procedure call message will be rejected due
 to an authentication error.  The reason for the failure will be
 "AUTH_REJECTEDCRED".  At this point, the client may wish to try the
 original "AUTH_UNIX" style of credentials.

9.3 DES Authentication

 UNIX authentication suffers from three major problems:
 (1) The naming is too UNIX oriented.
 (2) There is no universal name, uid, and gid space.
 (3) There is no verifier, so credentials can easily be faked.
 DES authentication attempts to address these problems.

9.3.1 Naming

 The first problem is handled by addressing the client by a simple
 string of characters instead of by an operating system specific
 integer.  This string of characters is known as the "netname" or
 network name of the client. The server is not allowed to interpret
 the contents of the client's name in any other way except to identify
 the client.  Thus, netnames should be unique for every client in the
 Internet.
 It is up to each operating system's implementation of DES
 authentication to generate netnames for its users that insure this
 uniqueness when they call upon remote servers.  Operating systems
 already know how to distinguish users local to their systems. It is
 usually a simple matter to extend this mechanism to the network.  For
 example, a UNIX user at Sun with a user ID of 515 might be assigned
 the following netname: "unix.515@sun.com".  This netname contains
 three items that serve to insure it is unique.  Going backwards,
 there is only one naming domain called "sun.com" in the Internet.
 Within this domain, there is only one UNIX user with user ID 515.
 However, there may be another user on another operating system, for
 example VMS, within the same naming domain that, by coincidence,
 happens to have the same user ID. To insure that these two users can
 be distinguished we add the operating system name. So one user is
 "unix.515@sun.com" and the other is "vms.515@sun.com".

Sun Microsystems [Page 13] RFC 1057 Remote Procedure Call, Version 2 June 1988

 The first field is actually a naming method rather than an operating
 system name.  It happens that today there is almost a one-to-one
 correspondence between naming methods and operating systems.  If the
 world could agree on a naming standard, the first field could be the
 name of that standard, instead of an operating system name.

9.3.2 DES Authentication Verifiers

 Unlike UNIX authentication, DES authentication does have a verifier
 so the server can validate the client's credential (and vice-versa).
 The contents of this verifier is primarily an encrypted timestamp.
 The server can decrypt this timestamp, and if it is close to the real
 time, then the client must have encrypted it correctly.  The only way
 the client could encrypt it correctly is to know the "conversation
 key" of the RPC session. And if the client knows the conversation
 key, then it must be the real client.
 The conversation key is a DES [5] key which the client generates and
 passes to the server in its first RPC call.  The conversation key is
 encrypted using a public key scheme in this first transaction.  The
 particular public key scheme used in DES authentication is Diffie-
 Hellman [3] with 192-bit keys.  The details of this encryption method
 are described later.
 The client and the server need the same notion of the current time in
 order for all of this to work, perhaps by using the Network Time
 Protocol [4].  If network time synchronization cannot be guaranteed,
 then the client can determine the server's time before beginning the
 conversation using a simpler time request protocol.
 The way a server determines if a client timestamp is valid is
 somewhat complicated. For any other transaction but the first, the
 server just checks for two things:
 (1) the timestamp is greater than the one  previously seen from the
 same client.
 (2) the timestamp has not expired.
 A timestamp is expired if the server's time is later than the sum of
 the client's timestamp plus what is known as the client's "window".
 The "window" is a number the client passes (encrypted) to the server
 in its first transaction.  You can think of it as a lifetime for the
 credential.
 This explains everything but the first transaction.  In the first
 transaction, the server checks only that the timestamp has not
 expired.  If this was all that was done though, then it would be
 quite easy for the client to send random data in place of the

Sun Microsystems [Page 14] RFC 1057 Remote Procedure Call, Version 2 June 1988

 timestamp with a fairly good chance of succeeding.  As an added
 check, the client sends an encrypted item in the first transaction
 known as the "window verifier" which must be equal to the window
 minus 1, or the server will reject the credential.
 The client too must check the verifier returned from the server to be
 sure it is legitimate.  The server sends back to the client the
 encrypted timestamp it received from the client, minus one second.
 If the client gets anything different than this, it will reject it.

9.3.3 Nicknames and Clock Synchronization

 After the first transaction, the server's DES authentication
 subsystem returns in its verifier to the client an integer "nickname"
 which the client may use in its further transactions instead of
 passing its netname, encrypted DES key and window every time. The
 nickname is most likely an index into a table on the server which
 stores for each client its netname, decrypted DES key and window.
 Though they originally were synchronized, the client's and server's
 clocks can get out of sync again.  When this happens the client RPC
 subsystem most likely will get back "RPC_AUTHERROR" at which point it
 should resynchronize.
 A client may still get the "RPC_AUTHERROR" error even though it is
 synchronized with the server.  The reason is that the server's
 nickname table is a limited size, and it may flush entries whenever
 it wants.  A client should resend its original credential in this
 case and the server will give it a new nickname.  If a server
 crashes, the entire nickname table gets flushed, and all clients will
 have to resend their original credentials.

9.3.4 DES Authentication Protocol Specification

 There are two kinds of credentials: one in which the client uses its
 full network name, and one in which it uses its "nickname" (just an
 unsigned integer) given to it by the server.  The client must use its
 fullname in its first transaction with the server, in which the
 server will return to the client its nickname.  The client may use
 its nickname in all further transactions with the server. There is no
 requirement to use the nickname, but it is wise to use it for
 performance reasons.
    enum authdes_namekind {
       ADN_FULLNAME = 0,
       ADN_NICKNAME = 1
    };

Sun Microsystems [Page 15] RFC 1057 Remote Procedure Call, Version 2 June 1988

 A 64-bit block of encrypted DES data:
 typedef opaque des_block[8];
 Maximum length of a network user's name:
 const MAXNETNAMELEN = 255;
 A fullname contains the network name of the client, an encrypted
 conversation key and the window. The window is actually a lifetime
 for the credential.  If the time indicated in the verifier timestamp
 plus the window has past, then the server should expire the request
 and not grant it.  To insure that requests are not replayed, the
 server should insist that timestamps are greater than the previous
 one seen, unless it is the first transaction.  In the first
 transaction, the server checks instead that the window verifier is
 one less than the window.
 struct authdes_fullname {
    string name<MAXNETNAMELEN>;  /* name of client                */
    des_block key;               /* PK encrypted conversation key */
    opaque window[4];            /* encrypted window              */
 };
 A credential is either a fullname or a nickname:
 union authdes_cred switch (authdes_namekind adc_namekind) {
 case ADN_FULLNAME:
    authdes_fullname adc_fullname;
 case ADN_NICKNAME:
    int adc_nickname;
 };
 A timestamp encodes the time since midnight,   March 1, 1970.
 struct timestamp {
    unsigned int seconds;    /* seconds          */
    unsigned int useconds;   /* and microseconds */
 };
 Verifier: client variety.
 The window verifier is only used in the first transaction.  In
 conjunction with a fullname credential, these items are packed into
 the following structure before being encrypted:

Sun Microsystems [Page 16] RFC 1057 Remote Procedure Call, Version 2 June 1988

 struct {
     adv_timestamp;        -- one DES block
     adc_fullname.window;  -- one half DES block
     adv_winverf;          -- one half DES block
 }
 This structure is encrypted using CBC mode encryption with an input
 vector of zero.  All other encryptions of timestamps use ECB mode
 encryption.
 struct authdes_verf_clnt {
    des_block adv_timestamp;    /* encrypted timestamp       */
    opaque adv_winverf[4];      /* encrypted window verifier */
 };
    Verifier: server variety.
 The server returns (encrypted) the same timestamp the client gave it
 minus one second.  It also tells the client its nickname to be used
 in future transactions (unencrypted).
 struct authdes_verf_svr {
    des_block adv_timeverf;     /* encrypted verifier      */
    int adv_nickname;      /* new nickname for client */
 };

9.3.5 Diffie-Hellman Encryption

 In this scheme, there are two constants "BASE" and "MODULUS" [3].
 The particular values Sun has chosen for these for the DES
 authentication protocol are:
 const BASE = 3;
 const MODULUS = "d4a0ba0250b6fd2ec626e7efd637df76c716e22d0944b88b"
 The way this scheme works is best explained by an example.  Suppose
 there are two people "A" and "B" who want to send encrypted messages
 to each other.  So, A and B both generate "secret" keys at random
 which they do not reveal to anyone.  Let these keys be represented as
 SK(A) and SK(B).  They also publish in a public directory their
 "public" keys. These keys are computed as follows:
       PK(A) = ( BASE ** SK(A) ) mod MODULUS
       PK(B) = ( BASE ** SK(B) ) mod MODULUS
 The "**" notation is used here to represent exponentiation. Now, both
 A and B can arrive at the "common" key between them, represented here
 as CK(A, B), without revealing their secret keys.

Sun Microsystems [Page 17] RFC 1057 Remote Procedure Call, Version 2 June 1988

 A computes:
    CK(A, B) = ( PK(B) ** SK(A)) mod MODULUS
 while B computes:
    CK(A, B) = ( PK(A) ** SK(B)) mod MODULUS
 These two can be shown to be equivalent:
    (PK(B) ** SK(A)) mod MODULUS = (PK(A) ** SK(B)) mod MODULUS
 We drop the "mod MODULUS" parts and assume modulo arithmetic to
 simplify things:
    PK(B) ** SK(A) = PK(A) ** SK(B)
 Then, replace PK(B) by what B computed earlier and likewise for PK(A).
    ((BASE ** SK(B)) ** SK(A) = (BASE ** SK(A)) ** SK(B)
 which leads to:
    BASE ** (SK(A) * SK(B)) = BASE ** (SK(A) * SK(B))
 This common key CK(A, B) is not used to encrypt the timestamps used
 in the protocol. Rather, it is used only to encrypt a conversation
 key which is then used to encrypt the timestamps.  The reason for
 doing this is to use the common key as little as possible, for fear
 that it could be broken.  Breaking the conversation key is a far less
 serious offense, since conversations are relatively short-lived.
 The conversation key is encrypted using 56-bit DES keys, yet the
 common key is 192 bits.  To reduce the number of bits, 56 bits are
 selected from the common key as follows. The middle-most 8-bytes are
 selected from the common key, and then parity is added to the lower
 order bit of each byte, producing a 56-bit key with 8 bits of parity.

10. RECORD MARKING STANDARD

 When RPC messages are passed on top of a byte stream transport
 protocol (like TCP), it is necessary to delimit one message from
 another in order to detect and possibly recover from protocol errors.
 This is called record marking (RM).  Sun uses this RM/TCP/IP
 transport for passing RPC messages on TCP streams.  One RPC message
 fits into one RM record.
 A record is composed of one or more record fragments.  A record

Sun Microsystems [Page 18] RFC 1057 Remote Procedure Call, Version 2 June 1988

 fragment is a four-byte header followed by 0 to (2**31) - 1 bytes of
 fragment data.  The bytes encode an unsigned binary number; as with
 XDR integers, the byte order is from highest to lowest.  The number
 encodes two values -- a boolean which indicates whether the fragment
 is the last fragment of the record (bit value 1 implies the fragment
 is the last fragment) and a 31-bit unsigned binary value which is the
 length in bytes of the fragment's data.  The boolean value is the
 highest-order bit of the header; the length is the 31 low-order bits.
 (Note that this record specification is NOT in XDR standard form!)

11. THE RPC LANGUAGE

 Just as there was a need to describe the XDR data-types in a formal
 language, there is also need to describe the procedures that operate
 on these XDR data-types in a formal language as well.  The RPC
 Language is an extension to the XDR language, with the addition of
 "program", "procedure", and "version" declarations.  The following
 example is used to describe the essence of the language.

Sun Microsystems [Page 19] RFC 1057 Remote Procedure Call, Version 2 June 1988

11.1 An Example Service Described in the RPC Language

 Here is an example of the specification of a simple ping program.
    program PING_PROG {
          /*
           * Latest and greatest version
           */
          version PING_VERS_PINGBACK {
             void
             PINGPROC_NULL(void) = 0;
             /*
              * Ping the client, return the round-trip time
              * (in microseconds). Returns -1 if the operation
              * timed out.
              */
             int
             PINGPROC_PINGBACK(void) = 1;
          } = 2;
          /*
           * Original version
           */
          version PING_VERS_ORIG {
             void
             PINGPROC_NULL(void) = 0;
          } = 1;
       } = 1;
       const PING_VERS = 2;      /* latest version */
 The first version described is PING_VERS_PINGBACK with two
 procedures, PINGPROC_NULL and PINGPROC_PINGBACK.  PINGPROC_NULL takes
 no arguments and returns no results, but it is useful for computing
 round-trip times from the client to the server and back again.  By
 convention, procedure 0 of any RPC protocol should have the same
 semantics, and never require any kind of authentication.  The second
 procedure is used for the client to have the server do a reverse ping
 operation back to the client, and it returns the amount of time (in
 microseconds) that the operation used.  The next version,
 PING_VERS_ORIG, is the original version of the protocol and it does
 not contain PINGPROC_PINGBACK procedure. It is useful for
 compatibility with old client programs, and as this program matures
 it may be dropped from the protocol entirely.

Sun Microsystems [Page 20] RFC 1057 Remote Procedure Call, Version 2 June 1988

11.2 The RPC Language Specification

 The RPC language is identical to the XDR language defined in RFC
 1014, except for the added definition of a "program-def" described
 below.
 program-def:
    "program" identifier "{"
       version-def
       version-def *
    "}" "=" constant ";"
 version-def:
    "version" identifier "{"
        procedure-def
        procedure-def *
    "}" "=" constant ";"
 procedure-def:
    type-specifier identifier "(" type-specifier
      ("," type-specifier )* ")" "=" constant ";"

11.3 Syntax Notes

 (1) The following keywords are added and cannot be used as
 identifiers: "program" and "version";
 (2) A version name cannot occur more than once within the scope of a
 program definition. Nor can a version number occur more than once
 within the scope of a program definition.
 (3) A procedure name cannot occur more than once within the scope of
 a version definition. Nor can a procedure number occur more than once
 within the scope of version definition.
 (4) Program identifiers are in the same name space as constant and
 type identifiers.
 (5) Only unsigned constants can be assigned to programs, versions and
 procedures.

Sun Microsystems [Page 21] RFC 1057 Remote Procedure Call, Version 2 June 1988

APPENDIX A: PORT MAPPER PROGRAM PROTOCOL

 The port mapper program maps RPC program and version numbers to
 transport-specific port numbers.  This program makes dynamic binding
 of remote programs possible.
 This is desirable because the range of reserved port numbers is very
 small and the number of potential remote programs is very large.  By
 running only the port mapper on a reserved port, the port numbers of
 other remote programs can be ascertained by querying the port mapper.
 The port mapper also aids in broadcast RPC.  A given RPC program will
 usually have different port number bindings on different machines, so
 there is no way to directly broadcast to all of these programs. The
 port mapper, however, does have a fixed port number.  So, to
 broadcast to a given program, the client actually sends its message
 to the port mapper located at the broadcast address. Each port mapper
 that picks up the broadcast then calls the local service specified by
 the client.  When the port mapper gets the reply from the local
 service, it sends the reply on back to the client.

A.1 Port Mapper Protocol Specification (in RPC Language)

       const PMAP_PORT = 111;      /* portmapper port number */
 A mapping of (program, version, protocol) to port number:
       struct mapping {
          unsigned int prog;
          unsigned int vers;
          unsigned int prot;
          unsigned int port;
       };
 Supported values for the "prot" field:
       const IPPROTO_TCP = 6;      /* protocol number for TCP/IP */
       const IPPROTO_UDP = 17;     /* protocol number for UDP/IP */
 A list of mappings:
       struct *pmaplist {
          mapping map;
          pmaplist next;
       };

Sun Microsystems [Page 22] RFC 1057 Remote Procedure Call, Version 2 June 1988

 Arguments to callit:
       struct call_args {
          unsigned int prog;
          unsigned int vers;
          unsigned int proc;
          opaque args<>;
       };
 Results of callit:
       struct call_result {
          unsigned int port;
          opaque res<>;
       };
 Port mapper procedures:
       program PMAP_PROG {
          version PMAP_VERS {
             void
             PMAPPROC_NULL(void)         = 0;
             bool
             PMAPPROC_SET(mapping)       = 1;
             bool
             PMAPPROC_UNSET(mapping)     = 2;
             unsigned int
             PMAPPROC_GETPORT(mapping)   = 3;
             pmaplist
             PMAPPROC_DUMP(void)         = 4;
             call_result
             PMAPPROC_CALLIT(call_args)  = 5;
          } = 2;
       } = 100000;

A.2 Port Mapper Operation

 The portmapper program currently supports two protocols (UDP and
 TCP).  The portmapper is contacted by talking to it on assigned port
 number 111 (SUNRPC) on either of these protocols.

Sun Microsystems [Page 23] RFC 1057 Remote Procedure Call, Version 2 June 1988

 The following is a description of each of the portmapper procedures:
 PMAPPROC_NULL:
 This procedure does no work.  By convention, procedure zero of any
 protocol takes no parameters and returns no results.
 PMAPPROC_SET:
 When a program first becomes available on a machine, it registers
 itself with the port mapper program on the same machine.  The program
 passes its program number "prog", version number "vers", transport
 protocol number "prot", and the port "port" on which it awaits
 service request.  The procedure returns a boolean reply whose value
 is "TRUE" if the procedure successfully established the mapping and
 "FALSE" otherwise.  The procedure refuses to establish a mapping if
 one already exists for the tuple "(prog, vers, prot)".
 PMAPPROC_UNSET:
 When a program becomes unavailable, it should unregister itself with
 the port mapper program on the same machine.  The parameters and
 results have meanings identical to those of "PMAPPROC_SET".  The
 protocol and port number fields of the argument are ignored.
 PMAPPROC_GETPORT:
 Given a program number "prog", version number "vers", and transport
 protocol number "prot", this procedure returns the port number on
 which the program is awaiting call requests.  A port value of zeros
 means the program has not been registered.  The "port" field of the
 argument is ignored.
 PMAPPROC_DUMP:
 This procedure enumerates all entries in the port mapper's database.
 The procedure takes no parameters and returns a list of program,
 version, protocol, and port values.
 PMAPPROC_CALLIT:
 This procedure allows a client to call another remote procedure on
 the same machine without knowing the remote procedure's port number.
 It is intended for supporting broadcasts to arbitrary remote programs
 via the well-known port mapper's port.  The parameters "prog",
 "vers", "proc", and the bytes of "args" are the program number,
 version number, procedure number, and parameters of the remote
 procedure.  Note:

Sun Microsystems [Page 24] RFC 1057 Remote Procedure Call, Version 2 June 1988

 (1) This procedure only sends a reply if the procedure was
 successfully executed and is silent (no reply) otherwise.
 (2) The port mapper communicates with the remote program using UDP
 only.
 The procedure returns the remote program's port number, and the reply
 is the reply of the remote procedure.

REFERENCES

 [1] Birrell, A. D.  & Nelson, B. J., "Implementing Remote Procedure
     Calls", XEROX CSL-83-7, October 1983.
 [2] Cheriton, D., "VMTP: Versatile Message Transaction Protocol",
     Preliminary Version 0.3, Stanford University, January 1987.
 [3] Diffie & Hellman, "New Directions in Cryptography", IEEE
     Transactions on Information Theory IT-22, November 1976.
 [4] Mills, D., "Network Time Protocol", RFC-958, M/A-COM Linkabit,
     September 1985.
 [5] National Bureau of Standards, "Data Encryption Standard", Federal
     Information Processing Standards Publication 46, January 1977.
 [6] Postel, J., "Transmission Control Protocol - DARPA Internet
     Program Protocol Specification", RFC-793, Information Sciences
     Institute, September 1981.
 [7] Postel, J., "User Datagram Protocol", RFC-768, Information
     Sciences Institute, August 1980.
 [8] Reynolds, J., and Postel, J., "Assigned Numbers", RFC-1010,
     Information Sciences Institute, May 1987.
 [9] Sun Microsystems, "XDR: External Data Representation Standard",
     RFC-1014, June 1987.

Sun Microsystems [Page 25]

/data/webs/external/dokuwiki/data/pages/rfc/rfc1057.txt · Last modified: 1988/06/24 18:25 by 127.0.0.1

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki