Network Working Group                             Sun Microsystems, Inc.
Request for Comments: 1050                        April 1988

                       RPC: Remote Procedure Call
                         Protocol Specification


   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.


   This document specifies a message protocol used in implementing 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 RPC or its uses.  The paper by Birrell and
   Nelson [1] is recommended as an excellent background to and
   justification of RPC.


   This document discusses servers, services, programs, procedures,
   clients, and versions.  A server is a piece of software where network
   services are implemented.  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).  Network clients are pieces of software
   that initiate remote procedure calls to services.  A server may
   support more than one version of a remote program in order to be
   forward 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
   IO and have procedures like "read" and "write".  A client machine of
   the network file service would call the procedures associated with
   the two programs of the service on behalf of some user on the client

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RFC 1050                 Remote Procedure Call                April 1988


   The remote procedure call model 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 result
   register).  It then transfers control to the procedure, and
   eventually gains back 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 is similar, in that one thread of control
   logically winds through two processes -- one is the caller's process,
   the other is a server's process.  That is, the caller process sends a
   call message to the server process and waits (blocks) for a reply
   message.  The call message contains the procedure's parameters, among
   other things.  The reply message contains the procedure's results,
   among other things.  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.

   Note that 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 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 task to process an
   incoming request, so that the server can be free to receive other


   The RPC protocol is independent of transport protocols.  That is, RPC
   does not care how a message is passed from one process to another.
   The protocol deals only with specification and interpretation of

   It is important to point out that RPC does not try to implement any
   kind of reliability and that the application must 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/IP [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/IP [7], it must implement
   its own retransmission and time-out policy as the RPC layer does not

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   provide this service.

   Because of transport independence, the RPC protocol does not attach
   specific semantics to the remote procedures or their execution.
   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/IP.  If an
   application retransmits RPC messages after short time-outs, the only
   thing it can infer if it receives no reply is that the procedure was
   executed zero or more times.  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
   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
   request.  The main use of this transaction is by the client RPC layer
   in matching replies to requests.  However, a client application may
   choose to reuse its previous transaction ID when retransmitting a
   request.  The server application, knowing this fact, may choose to
   remember this ID after granting a request and not regrant requests
   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/IP, 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 the most natural transport for RPC.

   Note:  At Sun, RPC is currently implemented on top of both TCP/IP and
   UDP/IP transports.


   The act of binding a client to a service is NOT part of the remote
   procedure call specification.  This important and necessary function
   is left up to some higher-level software.  (The software may use RPC
   itself; see Appendix A.)

   Implementors should think of the RPC protocol as the jump-subroutine
   instruction ("JSR") of a network; the loader (binder) makes JSR

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   useful, and the loader itself uses JSR to accomplish its task.
   Likewise, the network makes RPC useful, using RPC to accomplish this


   The RPC protocol provides the fields necessary for a client to
   identify itself to a service and vice-versa.  Security and access
   control mechanisms can be built on top of the 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".


   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

   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
      (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 fields:  remote program
   number, remote program version number, and remote procedure number.
   The three fields uniquely identify the procedure to be called.
   Program numbers are administered by some central authority (like
   Sun).  Once an implementor has a program number, he can implement his
   remote program; the first implementation would most likely have the
   version number of 1.  Because most new protocols evolve into better,
   stable, and mature protocols, 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.

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   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 speak protocol version 2.
          The lowest and highest supported RPC version numbers are

      (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 caller 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.)

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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:

         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 simple English, any "opaque_auth" structure is an "auth_flavor"
   enumeration followed by bytes which are opaque to the RPC protocol

   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 response message
   contains information stating why they were rejected.

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

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   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.
   That is, each call message is matched with a response message.
   However, the protocol itself is a message-passing protocol with which
   other (non-RPC) protocols can be implemented.  Sun currently uses, or
   perhaps abuses, the RPC message protocol for the following two (non-
   RPC) protocols:  batching (or pipelining) and broadcast RPC.  These
   two protocols are discussed but not defined below.

7.4.1 Batching

   Batching allows a client to send an arbitrarily large sequence of
   call messages to a server; batching typically uses reliable byte
   stream protocols (like TCP/IP) 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 requests.  A sequence of batch
   calls is usually terminated by a legitimate RPC in order to flush the
   pipeline (with positive acknowledgement).

7.4.2 Broadcast RPC

   In broadcast RPC-based protocols, the client sends a broadcast packet
   to the network and waits for numerous replies.  Broadcast RPC uses
   unreliable, packet-based protocols (like UDP/IP) as its transports.
   Servers that support broadcast protocols only respond when the
   request is successfully processed, and are silent in the face of
   errors.  Broadcast RPC uses the Port Mapper RPC service to achieve
   its semantics.  (See Appendix A for more information.)


   This section defines the RPC message protocol in the XDR data
   description language.  The message is defined in a top-down style.

       enum msg_type {
          CALL  = 0,
          REPLY = 1

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        * 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 */

        * 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

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        * 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 request 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.
       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 request:
        * The call message was either accepted or rejected.
       union reply_body switch (reply_stat stat) {
       case MSG_ACCEPTED:
          accepted_reply areply;
       case MSG_DENIED:
          rejected_reply rreply;
       } reply;


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        * Reply to an RPC request that was accepted by the server:
        * there could be an error even though the request was accepted.
        * The first field is an authentication verifier that the server
        * generates in order to validate itself to the caller.  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.
       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;
               * Void.  Cases include PROG_UNAVAIL, PROC_UNAVAIL,
               * and GARBAGE_ARGS.
           } reply_data;

        * Reply to an RPC request that was rejected by the server:
        * The request 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;

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          } mismatch_info;
       case AUTH_ERROR:
          auth_stat stat;


   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 caller does not know who he is or
   the server does not care who the caller is.  In this case, the flavor
   value (the discriminant of the opaque_auth's union) of the RPC
   message's credentials, verifier, and response 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 caller of a remote procedure may wish to identify himself as he
   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<10>;

   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

   The value of the discriminant of the response verifier received in
   the reply message from the server may be "AUTH_NULL" or "AUTH_SHORT".

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   In the case of "AUTH_SHORT", the bytes of the response 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
   credentials.  The server keeps a cache which maps shorthand opaque
   structures (passed back by way of an "AUTH_SHORT" style response
   verifier) to the original credentials of the caller.  The caller can
   save network bandwidth and server cpu cycles by using the new

   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 caller may wish to try the
   original "AUTH_UNIX" style of credentials.

9.3 DES Authentication

   UNIX authentication suffers from two major problems:

         (1) The naming is too UNIX oriented.
         (2) There is no verifier, so credentials can easily be faked.

   DES authentication attempts to fix these two problems.

9.3.1 Naming

   The first problem is handled by addressing the caller 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 caller.  The server is not allowed to interpret
   the contents of the caller's name in any other way except to identify
   the caller.  Thus, netnames should be unique for every caller in the

   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: "".  This netname contains
   three items that serve to insure it is unique.  Going backwards,
   there is only one naming domain called "" 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

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   "" and the other is "".

   The first field is actually a naming method rather than an operating
   system name.  It just 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 what the
   real time is, 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
   notifies the server of 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 128-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.  If network time synchronization
   cannot be guaranteed, then client can synchronize with the server
   before beginning the conversation, perhaps by consulting the Internet
   Time Server (TIME [4]).

   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

   This explains everything but the first transaction.  In the first

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   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
   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 (in XDR language)

     * 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 {

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       ADN_FULLNAME = 0,
       ADN_NICKNAME = 1

     * 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 */
       unsigned int window;         /* 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:
       unsigned int adc_nickname;

     * A timestamp encodes the time since midnight, January 1, 1970.
    struct timestamp {
         unsigned int seconds;    /* seconds          */
         unsigned int useconds;   /* and microseconds */

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     * 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:
     * 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 {
       timestamp adv_timestamp;    /* encrypted timestamp       */
       unsigned int adv_winverf;   /* 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 {
       timestamp adv_timeverf;     /* encrypted verifier      */
       unsigned int adv_nickname;  /* new nickname for client */

9.3.5 Diffie-Hellman Encryption

   In this scheme, there are two constants "PROOT" and "MODULUS".  The
   particular values Sun has chosen for these for the DES authentication
   protocol are:

        const PROOT = 2;
        const MODULUS = "b520985fb31fcaf75036701e37d8b857"; /* in hex */

   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:

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            PK(A) = ( PROOT ** SK(A) ) mod MODULUS
            PK(B) = ( PROOT ** 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.

         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

            ((PROOT ** SK(B)) ** SK(A) = (PROOT ** SK(A)) ** SK(B)

         which leads to:

            PROOT ** (SK(A) * SK(B)) = PROOT ** (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 128 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.

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RFC 1050                 Remote Procedure Call                April 1988


   When RPC messages are passed on top of a byte stream protocol (like
   TCP/IP), it is necessary, or at least desirable, to delimit one
   message from another in order to detect and possibly recover from
   user 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
   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!)


   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.  We use the RPC
   Language for this purpose.  It is an extension to the XDR language.
   The following example is used to describe the essence of the

11.1 An Example Service Described in the RPC Language

   Here is an example of the specification of a simple ping program:

          * Simple ping program
         program PING_PROG {
             * Latest and greatest version
            version PING_VERS_PINGBACK {
               PINGPROC_NULL(void) = 0;

                * Ping the caller, return the round-trip time
                * (in microseconds).  Returns -1 if the operation
                * timed out.

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               PINGPROC_PINGBACK(void) = 1;
            } = 2;

             * Original version
            version PING_VERS_ORIG {
               PINGPROC_NULL(void) = 0;
            } = 1;
         } = 1;

         const PING_VERS = 2;      /* latest version */

   The first version described is PING_VERS_PINGBACK with two
   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.

11.1 The RPC Language Specification

   The RPC language is identical to the XDR language, except for the
   added definition of a "program-def" described below.

         "program" identifier "{"
             version-def *
         "}" "=" constant ";"

         "version" identifier "{"
             procedure-def *
         "}" "=" constant ";"


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         type-specifier identifier "(" type-specifier ")"
         "=" constant ";"

11.2 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.


   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 */

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       * 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;
       * 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 {
            PMAPPROC_NULL(void)         = 0;

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            PMAPPROC_SET(mapping)       = 1;

            PMAPPROC_UNSET(mapping)     = 2;

            unsigned int
            PMAPPROC_GETPORT(mapping)   = 3;

            PMAPPROC_DUMP(void)         = 4;

            PMAPPROC_CALLIT(call_args)  = 5;
         } = 2;
      } = 100000;

A.2 Port Mapper Operation

   The portmapper program currently supports two protocols (UDP/IP and
   TCP/IP).  The portmapper is contacted by talking to it on assigned
   port number 111 (SUNRPC [8]) on either of these protocols.  The
   following is a description of each of the portmapper procedures:


         This procedure does no work.  By convention, procedure zero of
         any protocol takes no parameters and returns no results.


         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 response 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)".


         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.

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RFC 1050                 Remote Procedure Call                April 1988


         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.


         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.


         This procedure allows a caller 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:

            (1) This procedure only sends a response if the procedure
                 was successfully executed and is silent (no response)

            (2) The port mapper communicates with the remote program
                using UDP/IP only.

         The procedure returns the remote program's port number, and the
         bytes of results are the results of the remote procedure.


   [1]  Birrel, A. D., and Nelson, B. J., "Implementing Remote
        Procedure Calls", XEROX CSL-83-7, October 1983.

   [2]  Cheriton, D., "VMTP: Versatile Message Transaction Protocol",
        Version 0.7, RFC-1045, Stanford University, February 1988.

   [3]  Diffie & Hellman, "Net Directions in Cryptography", IEEE
        Transactions on Information Theory IT-22, November 1976.

   [4]  Postel, J., and Harrenstien, K., "Time Protocol", RFC-868,
        Network Information Center, SRI, May 1983.

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RFC 1050                 Remote Procedure Call                April 1988

   [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; Network Information
        Center, SRI, September 1981.

   [7]  Postel, J., "User Datagram Protocol", RFC-768, Network
        Information Center, SRI, August 1980.

   [8]  Reynolds, J. and Postel, J.; "Assigned Numbers", RFC-1010,
        Network Information Center, SRI, May 1987.

   [9]  Sun Microsystems; "XDR:  External Data Representation
        Standard", RFC-1014; Sun Microsystems, June 1987.

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