/share/doc/psd/26.rpcrfc/rpc.rfc.ms

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  13. .OH 'Remote Procedure Calls: Protocol Specification''Page %'
  14. .EH 'Page %''Remote Procedure Calls: Protocol Specification'
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  16. .SH
  17. \&Remote Procedure Calls: Protocol Specification
  18. .LP
  19. .NH 0
  20. \&Status of this Memo
  21. .LP
  22. Note: This chapter specifies a protocol that Sun Microsystems, Inc.,
  23. and others are using.
  24. It has been designated RFC1050 by the ARPA Network
  25. Information Center.
  26. .LP
  27. .NH 1
  28. \&Introduction
  29. .LP
  30. This chapter specifies a message protocol used in implementing
  31. Sun's Remote Procedure Call (RPC) package. (The message protocol is
  32. specified with the External Data Representation (XDR) language.
  33. See the
  34. .I "External Data Representation Standard: Protocol Specification"
  35. for the details. Here, we assume that the reader is familiar
  36. with XDR and do not attempt to justify it or its uses). The paper
  37. by Birrell and Nelson [1] is recommended as an excellent background
  38. to and justification of RPC.
  39. .NH 2
  40. \&Terminology
  41. .LP
  42. This chapter discusses servers, services, programs, procedures,
  43. clients, and versions. A server is a piece of software where network
  44. services are implemented. A network service is a collection of one
  45. or more remote programs. A remote program implements one or more
  46. remote procedures; the procedures, their parameters, and results are
  47. documented in the specific program's protocol specification (see the
  48. \fIPort Mapper Program Protocol\fP\, below, for an example). Network
  49. clients are pieces of software that initiate remote procedure calls
  50. to services. A server may support more than one version of a remote
  51. program in order to be forward compatible with changing protocols.
  52. .LP
  53. For example, a network file service may be composed of two programs.
  54. One program may deal with high-level applications such as file system
  55. access control and locking. The other may deal with low-level file
  56. IO and have procedures like "read" and "write". A client machine of
  57. the network file service would call the procedures associated with
  58. the two programs of the service on behalf of some user on the client
  59. machine.
  60. .NH 2
  61. \&The RPC Model
  62. .LP
  63. The remote procedure call model is similar to the local procedure
  64. call model. In the local case, the caller places arguments to a
  65. procedure in some well-specified location (such as a result
  66. register). It then transfers control to the procedure, and
  67. eventually gains back control. At that point, the results of the
  68. procedure are extracted from the well-specified location, and the
  69. caller continues execution.
  70. .LP
  71. The remote procedure call is similar, in that one thread of control
  72. logically winds through two processes\(emone is the caller's process,
  73. the other is a server's process. That is, the caller process sends a
  74. call message to the server process and waits (blocks) for a reply
  75. message. The call message contains the procedure's parameters, among
  76. other things. The reply message contains the procedure's results,
  77. among other things. Once the reply message is received, the results
  78. of the procedure are extracted, and caller's execution is resumed.
  79. .LP
  80. On the server side, a process is dormant awaiting the arrival of a
  81. call message. When one arrives, the server process extracts the
  82. procedure's parameters, computes the results, sends a reply message,
  83. and then awaits the next call message.
  84. .LP
  85. Note that in this model, only one of the two processes is active at
  86. any given time. However, this model is only given as an example.
  87. The RPC protocol makes no restrictions on the concurrency model
  88. implemented, and others are possible. For example, an implementation
  89. may choose to have RPC calls be asynchronous, so that the client may
  90. do useful work while waiting for the reply from the server. Another
  91. possibility is to have the server create a task to process an
  92. incoming request, so that the server can be free to receive other
  93. requests.
  94. .NH 2
  95. \&Transports and Semantics
  96. .LP
  97. The RPC protocol is independent of transport protocols. That is, RPC
  98. does not care how a message is passed from one process to another.
  99. The protocol deals only with specification and interpretation of
  100. messages.
  101. .LP
  102. It is important to point out that RPC does not try to implement any
  103. kind of reliability and that the application must be aware of the
  104. type of transport protocol underneath RPC. If it knows it is running
  105. on top of a reliable transport such as TCP/IP[6], then most of the
  106. work is already done for it. On the other hand, if it is running on
  107. top of an unreliable transport such as UDP/IP[7], it must implement
  108. is own retransmission and time-out policy as the RPC layer does not
  109. provide this service.
  110. .LP
  111. Because of transport independence, the RPC protocol does not attach
  112. specific semantics to the remote procedures or their execution.
  113. Semantics can be inferred from (but should be explicitly specified
  114. by) the underlying transport protocol. For example, consider RPC
  115. running on top of an unreliable transport such as UDP/IP. If an
  116. application retransmits RPC messages after short time-outs, the only
  117. thing it can infer if it receives no reply is that the procedure was
  118. executed zero or more times. If it does receive a reply, then it can
  119. infer that the procedure was executed at least once.
  120. .LP
  121. A server may wish to remember previously granted requests from a
  122. client and not regrant them in order to insure some degree of
  123. execute-at-most-once semantics. A server can do this by taking
  124. advantage of the transaction ID that is packaged with every RPC
  125. request. The main use of this transaction is by the client RPC layer
  126. in matching replies to requests. However, a client application may
  127. choose to reuse its previous transaction ID when retransmitting a
  128. request. The server application, knowing this fact, may choose to
  129. remember this ID after granting a request and not regrant requests
  130. with the same ID in order to achieve some degree of
  131. execute-at-most-once semantics. The server is not allowed to examine
  132. this ID in any other way except as a test for equality.
  133. .LP
  134. On the other hand, if using a reliable transport such as TCP/IP, the
  135. application can infer from a reply message that the procedure was
  136. executed exactly once, but if it receives no reply message, it cannot
  137. assume the remote procedure was not executed. Note that even if a
  138. connection-oriented protocol like TCP is used, an application still
  139. needs time-outs and reconnection to handle server crashes.
  140. .LP
  141. There are other possibilities for transports besides datagram- or
  142. connection-oriented protocols. For example, a request-reply protocol
  143. such as VMTP[2] is perhaps the most natural transport for RPC.
  144. .SH
  145. .I
  146. NOTE: At Sun, RPC is currently implemented on top of both TCP/IP
  147. and UDP/IP transports.
  148. .LP
  149. .NH 2
  150. \&Binding and Rendezvous Independence
  151. .LP
  152. The act of binding a client to a service is NOT part of the remote
  153. procedure call specification. This important and necessary function
  154. is left up to some higher-level software. (The software may use RPC
  155. itself\(emsee the \fIPort Mapper Program Protocol\fP\, below).
  156. .LP
  157. Implementors should think of the RPC protocol as the jump-subroutine
  158. instruction ("JSR") of a network; the loader (binder) makes JSR
  159. useful, and the loader itself uses JSR to accomplish its task.
  160. Likewise, the network makes RPC useful, using RPC to accomplish this
  161. task.
  162. .NH 2
  163. \&Authentication
  164. .LP
  165. The RPC protocol provides the fields necessary for a client to
  166. identify itself to a service and vice-versa. Security and access
  167. control mechanisms can be built on top of the message authentication.
  168. Several different authentication protocols can be supported. A field
  169. in the RPC header indicates which protocol is being used. More
  170. information on specific authentication protocols can be found in the
  171. \fIAuthentication Protocols\fP\,
  172. below.
  173. .KS
  174. .NH 1
  175. \&RPC Protocol Requirements
  176. .LP
  177. The RPC protocol must provide for the following:
  178. .IP 1.
  179. Unique specification of a procedure to be called.
  180. .IP 2.
  181. Provisions for matching response messages to request messages.
  182. .KE
  183. .IP 3.
  184. Provisions for authenticating the caller to service and vice-versa.
  185. .LP
  186. Besides these requirements, features that detect the following are
  187. worth supporting because of protocol roll-over errors, implementation
  188. bugs, user error, and network administration:
  189. .IP 1.
  190. RPC protocol mismatches.
  191. .IP 2.
  192. Remote program protocol version mismatches.
  193. .IP 3.
  194. Protocol errors (such as misspecification of a procedure's parameters).
  195. .IP 4.
  196. Reasons why remote authentication failed.
  197. .IP 5.
  198. Any other reasons why the desired procedure was not called.
  199. .NH 2
  200. \&Programs and Procedures
  201. .LP
  202. The RPC call message has three unsigned fields: remote program
  203. number, remote program version number, and remote procedure number.
  204. The three fields uniquely identify the procedure to be called.
  205. Program numbers are administered by some central authority (like
  206. Sun). Once an implementor has a program number, he can implement his
  207. remote program; the first implementation would most likely have the
  208. version number of 1. Because most new protocols evolve into better,
  209. stable, and mature protocols, a version field of the call message
  210. identifies which version of the protocol the caller is using.
  211. Version numbers make speaking old and new protocols through the same
  212. server process possible.
  213. .LP
  214. The procedure number identifies the procedure to be called. These
  215. numbers are documented in the specific program's protocol
  216. specification. For example, a file service's protocol specification
  217. may state that its procedure number 5 is "read" and procedure number
  218. 12 is "write".
  219. .LP
  220. Just as remote program protocols may change over several versions,
  221. the actual RPC message protocol could also change. Therefore, the
  222. call message also has in it the RPC version number, which is always
  223. equal to two for the version of RPC described here.
  224. .LP
  225. The reply message to a request message has enough information to
  226. distinguish the following error conditions:
  227. .IP 1.
  228. The remote implementation of RPC does speak protocol version 2.
  229. The lowest and highest supported RPC version numbers are returned.
  230. .IP 2.
  231. The remote program is not available on the remote system.
  232. .IP 3.
  233. The remote program does not support the requested version number.
  234. The lowest and highest supported remote program version numbers are
  235. returned.
  236. .IP 4.
  237. The requested procedure number does not exist. (This is usually a
  238. caller side protocol or programming error.)
  239. .IP 5.
  240. The parameters to the remote procedure appear to be garbage from the
  241. server's point of view. (Again, this is usually caused by a
  242. disagreement about the protocol between client and service.)
  243. .NH 2
  244. \&Authentication
  245. .LP
  246. Provisions for authentication of caller to service and vice-versa are
  247. provided as a part of the RPC protocol. The call message has two
  248. authentication fields, the credentials and verifier. The reply
  249. message has one authentication field, the response verifier. The RPC
  250. protocol specification defines all three fields to be the following
  251. opaque type:
  252. .DS
  253. .ft CW
  254. .vs 11
  255. enum auth_flavor {
  256. AUTH_NULL = 0,
  257. AUTH_UNIX = 1,
  258. AUTH_SHORT = 2,
  259. AUTH_DES = 3
  260. /* \fIand more to be defined\fP */
  261. };
  262. struct opaque_auth {
  263. auth_flavor flavor;
  264. opaque body<400>;
  265. };
  266. .DE
  267. .LP
  268. In simple English, any
  269. .I opaque_auth
  270. structure is an
  271. .I auth_flavor
  272. enumeration followed by bytes which are opaque to the RPC protocol
  273. implementation.
  274. .LP
  275. The interpretation and semantics of the data contained within the
  276. authentication fields is specified by individual, independent
  277. authentication protocol specifications. (See
  278. \fIAuthentication Protocols\fP\,
  279. below, for definitions of the various authentication protocols.)
  280. .LP
  281. If authentication parameters were rejected, the response message
  282. contains information stating why they were rejected.
  283. .NH 2
  284. \&Program Number Assignment
  285. .LP
  286. Program numbers are given out in groups of
  287. .I 0x20000000
  288. (decimal 536870912) according to the following chart:
  289. .TS
  290. box tab (&) ;
  291. lfI lfI
  292. rfL cfI .
  293. Program Numbers&Description
  294. _
  295. .sp .5
  296. 0 - 1fffffff&Defined by Sun
  297. 20000000 - 3fffffff&Defined by user
  298. 40000000 - 5fffffff&Transient
  299. 60000000 - 7fffffff&Reserved
  300. 80000000 - 9fffffff&Reserved
  301. a0000000 - bfffffff&Reserved
  302. c0000000 - dfffffff&Reserved
  303. e0000000 - ffffffff&Reserved
  304. .TE
  305. .LP
  306. The first group is a range of numbers administered by Sun
  307. Microsystems and should be identical for all sites. The second range
  308. is for applications peculiar to a particular site. This range is
  309. intended primarily for debugging new programs. When a site develops
  310. an application that might be of general interest, that application
  311. should be given an assigned number in the first range. The third
  312. group is for applications that generate program numbers dynamically.
  313. The final groups are reserved for future use, and should not be used.
  314. .NH 2
  315. \&Other Uses of the RPC Protocol
  316. .LP
  317. The intended use of this protocol is for calling remote procedures.
  318. That is, each call message is matched with a response message.
  319. However, the protocol itself is a message-passing protocol with which
  320. other (non-RPC) protocols can be implemented. Sun currently uses, or
  321. perhaps abuses, the RPC message protocol for the following two
  322. (non-RPC) protocols: batching (or pipelining) and broadcast RPC.
  323. These two protocols are discussed but not defined below.
  324. .NH 3
  325. \&Batching
  326. .LP
  327. Batching allows a client to send an arbitrarily large sequence of
  328. call messages to a server; batching typically uses reliable byte
  329. stream protocols (like TCP/IP) for its transport. In the case of
  330. batching, the client never waits for a reply from the server, and the
  331. server does not send replies to batch requests. A sequence of batch
  332. calls is usually terminated by a legitimate RPC in order to flush the
  333. pipeline (with positive acknowledgement).
  334. .NH 3
  335. \&Broadcast RPC
  336. .LP
  337. In broadcast RPC-based protocols, the client sends a broadcast packet
  338. to the network and waits for numerous replies. Broadcast RPC uses
  339. unreliable, packet-based protocols (like UDP/IP) as its transports.
  340. Servers that support broadcast protocols only respond when the
  341. request is successfully processed, and are silent in the face of
  342. errors. Broadcast RPC uses the Port Mapper RPC service to achieve
  343. its semantics. See the \fIPort Mapper Program Protocol\fP\, below,
  344. for more information.
  345. .KS
  346. .NH 1
  347. \&The RPC Message Protocol
  348. .LP
  349. This section defines the RPC message protocol in the XDR data
  350. description language. The message is defined in a top-down style.
  351. .ie t .DS
  352. .el .DS L
  353. .ft CW
  354. enum msg_type {
  355. CALL = 0,
  356. REPLY = 1
  357. };
  358. .ft I
  359. /*
  360. * A reply to a call message can take on two forms:
  361. * The message was either accepted or rejected.
  362. */
  363. .ft CW
  364. enum reply_stat {
  365. MSG_ACCEPTED = 0,
  366. MSG_DENIED = 1
  367. };
  368. .ft I
  369. /*
  370. * Given that a call message was accepted, the following is the
  371. * status of an attempt to call a remote procedure.
  372. */
  373. .ft CW
  374. enum accept_stat {
  375. SUCCESS = 0, /* \fIRPC executed successfully \fP*/
  376. PROG_UNAVAIL = 1, /* \fIremote hasn't exported program \fP*/
  377. PROG_MISMATCH = 2, /* \fIremote can't support version # \fP*/
  378. PROC_UNAVAIL = 3, /* \fIprogram can't support procedure \fP*/
  379. GARBAGE_ARGS = 4 /* \fIprocedure can't decode params \fP*/
  380. };
  381. .DE
  382. .ie t .DS
  383. .el .DS L
  384. .ft I
  385. /*
  386. * Reasons why a call message was rejected:
  387. */
  388. .ft CW
  389. enum reject_stat {
  390. RPC_MISMATCH = 0, /* \fIRPC version number != 2 \fP*/
  391. AUTH_ERROR = 1 /* \fIremote can't authenticate caller \fP*/
  392. };
  393. .ft I
  394. /*
  395. * Why authentication failed:
  396. */
  397. .ft CW
  398. enum auth_stat {
  399. AUTH_BADCRED = 1, /* \fIbad credentials \fP*/
  400. AUTH_REJECTEDCRED = 2, /* \fIclient must begin new session \fP*/
  401. AUTH_BADVERF = 3, /* \fIbad verifier \fP*/
  402. AUTH_REJECTEDVERF = 4, /* \fIverifier expired or replayed \fP*/
  403. AUTH_TOOWEAK = 5 /* \fIrejected for security reasons \fP*/
  404. };
  405. .DE
  406. .KE
  407. .ie t .DS
  408. .el .DS L
  409. .ft I
  410. /*
  411. * The RPC message:
  412. * All messages start with a transaction identifier, xid,
  413. * followed by a two-armed discriminated union. The union's
  414. * discriminant is a msg_type which switches to one of the two
  415. * types of the message. The xid of a \fIREPLY\fP message always
  416. * matches that of the initiating \fICALL\fP message. NB: The xid
  417. * field is only used for clients matching reply messages with
  418. * call messages or for servers detecting retransmissions; the
  419. * service side cannot treat this id as any type of sequence
  420. * number.
  421. */
  422. .ft CW
  423. struct rpc_msg {
  424. unsigned int xid;
  425. union switch (msg_type mtype) {
  426. case CALL:
  427. call_body cbody;
  428. case REPLY:
  429. reply_body rbody;
  430. } body;
  431. };
  432. .DE
  433. .ie t .DS
  434. .el .DS L
  435. .ft I
  436. /*
  437. * Body of an RPC request call:
  438. * In version 2 of the RPC protocol specification, rpcvers must
  439. * be equal to 2. The fields prog, vers, and proc specify the
  440. * remote program, its version number, and the procedure within
  441. * the remote program to be called. After these fields are two
  442. * authentication parameters: cred (authentication credentials)
  443. * and verf (authentication verifier). The two authentication
  444. * parameters are followed by the parameters to the remote
  445. * procedure, which are specified by the specific program
  446. * protocol.
  447. */
  448. .ft CW
  449. struct call_body {
  450. unsigned int rpcvers; /* \fImust be equal to two (2) \fP*/
  451. unsigned int prog;
  452. unsigned int vers;
  453. unsigned int proc;
  454. opaque_auth cred;
  455. opaque_auth verf;
  456. /* \fIprocedure specific parameters start here \fP*/
  457. };
  458. .DE
  459. .ie t .DS
  460. .el .DS L
  461. .ft I
  462. /*
  463. * Body of a reply to an RPC request:
  464. * The call message was either accepted or rejected.
  465. */
  466. .ft CW
  467. union reply_body switch (reply_stat stat) {
  468. case MSG_ACCEPTED:
  469. accepted_reply areply;
  470. case MSG_DENIED:
  471. rejected_reply rreply;
  472. } reply;
  473. .DE
  474. .ie t .DS
  475. .el .DS L
  476. .ft I
  477. /*
  478. * Reply to an RPC request that was accepted by the server:
  479. * there could be an error even though the request was accepted.
  480. * The first field is an authentication verifier that the server
  481. * generates in order to validate itself to the caller. It is
  482. * followed by a union whose discriminant is an enum
  483. * accept_stat. The \fISUCCESS\fP arm of the union is protocol
  484. * specific. The \fIPROG_UNAVAIL\fP, \fIPROC_UNAVAIL\fP, and \fIGARBAGE_ARGP\fP
  485. * arms of the union are void. The \fIPROG_MISMATCH\fP arm specifies
  486. * the lowest and highest version numbers of the remote program
  487. * supported by the server.
  488. */
  489. .ft CW
  490. struct accepted_reply {
  491. opaque_auth verf;
  492. union switch (accept_stat stat) {
  493. case SUCCESS:
  494. opaque results[0];
  495. /* \fIprocedure-specific results start here\fP */
  496. case PROG_MISMATCH:
  497. struct {
  498. unsigned int low;
  499. unsigned int high;
  500. } mismatch_info;
  501. default:
  502. .ft I
  503. /*
  504. * Void. Cases include \fIPROG_UNAVAIL, PROC_UNAVAIL\fP,
  505. * and \fIGARBAGE_ARGS\fP.
  506. */
  507. .ft CW
  508. void;
  509. } reply_data;
  510. };
  511. .DE
  512. .ie t .DS
  513. .el .DS L
  514. .ft I
  515. /*
  516. * Reply to an RPC request that was rejected by the server:
  517. * The request can be rejected for two reasons: either the
  518. * server is not running a compatible version of the RPC
  519. * protocol (\fIRPC_MISMATCH\fP), or the server refuses to
  520. * authenticate the caller (\fIAUTH_ERROR\fP). In case of an RPC
  521. * version mismatch, the server returns the lowest and highest
  522. * supported RPC version numbers. In case of refused
  523. * authentication, failure status is returned.
  524. */
  525. .ft CW
  526. union rejected_reply switch (reject_stat stat) {
  527. case RPC_MISMATCH:
  528. struct {
  529. unsigned int low;
  530. unsigned int high;
  531. } mismatch_info;
  532. case AUTH_ERROR:
  533. auth_stat stat;
  534. };
  535. .DE
  536. .NH 1
  537. \&Authentication Protocols
  538. .LP
  539. As previously stated, authentication parameters are opaque, but
  540. open-ended to the rest of the RPC protocol. This section defines
  541. some "flavors" of authentication implemented at (and supported by)
  542. Sun. Other sites are free to invent new authentication types, with
  543. the same rules of flavor number assignment as there is for program
  544. number assignment.
  545. .NH 2
  546. \&Null Authentication
  547. .LP
  548. Often calls must be made where the caller does not know who he is or
  549. the server does not care who the caller is. In this case, the flavor
  550. value (the discriminant of the \fIopaque_auth\fP's union) of the RPC
  551. message's credentials, verifier, and response verifier is
  552. .I AUTH_NULL .
  553. The bytes of the opaque_auth's body are undefined.
  554. It is recommended that the opaque length be zero.
  555. .NH 2
  556. \&UNIX Authentication
  557. .LP
  558. The caller of a remote procedure may wish to identify himself as he
  559. is identified on a UNIX system. The value of the credential's
  560. discriminant of an RPC call message is
  561. .I AUTH_UNIX .
  562. The bytes of
  563. the credential's opaque body encode the following structure:
  564. .DS
  565. .ft CW
  566. struct auth_unix {
  567. unsigned int stamp;
  568. string machinename<255>;
  569. unsigned int uid;
  570. unsigned int gid;
  571. unsigned int gids<10>;
  572. };
  573. .DE
  574. The
  575. .I stamp
  576. is an arbitrary ID which the caller machine may
  577. generate. The
  578. .I machinename
  579. is the name of the caller's machine (like "krypton"). The
  580. .I uid
  581. is the caller's effective user ID. The
  582. .I gid
  583. is the caller's effective group ID. The
  584. .I gids
  585. is a
  586. counted array of groups which contain the caller as a member. The
  587. verifier accompanying the credentials should be of
  588. .I AUTH_NULL
  589. (defined above).
  590. .LP
  591. The value of the discriminant of the response verifier received in
  592. the reply message from the server may be
  593. .I AUTH_NULL
  594. or
  595. .I AUTH_SHORT .
  596. In the case of
  597. .I AUTH_SHORT ,
  598. the bytes of the response verifier's string encode an opaque
  599. structure. This new opaque structure may now be passed to the server
  600. instead of the original
  601. .I AUTH_UNIX
  602. flavor credentials. The server keeps a cache which maps shorthand
  603. opaque structures (passed back by way of an
  604. .I AUTH_SHORT
  605. style response verifier) to the original credentials of the caller.
  606. The caller can save network bandwidth and server cpu cycles by using
  607. the new credentials.
  608. .LP
  609. The server may flush the shorthand opaque structure at any time. If
  610. this happens, the remote procedure call message will be rejected due
  611. to an authentication error. The reason for the failure will be
  612. .I AUTH_REJECTEDCRED .
  613. At this point, the caller may wish to try the original
  614. .I AUTH_UNIX
  615. style of credentials.
  616. .KS
  617. .NH 2
  618. \&DES Authentication
  619. .LP
  620. UNIX authentication suffers from two major problems:
  621. .IP 1.
  622. The naming is too UNIX-system oriented.
  623. .IP 2.
  624. There is no verifier, so credentials can easily be faked.
  625. .LP
  626. DES authentication attempts to fix these two problems.
  627. .KE
  628. .NH 3
  629. \&Naming
  630. .LP
  631. The first problem is handled by addressing the caller by a simple
  632. string of characters instead of by an operating system specific
  633. integer. This string of characters is known as the "netname" or
  634. network name of the caller. The server is not allowed to interpret
  635. the contents of the caller's name in any other way except to
  636. identify the caller. Thus, netnames should be unique for every
  637. caller in the internet.
  638. .LP
  639. It is up to each operating system's implementation of DES
  640. authentication to generate netnames for its users that insure this
  641. uniqueness when they call upon remote servers. Operating systems
  642. already know how to distinguish users local to their systems. It is
  643. usually a simple matter to extend this mechanism to the network.
  644. For example, a UNIX user at Sun with a user ID of 515 might be
  645. assigned the following netname: "unix.515@sun.com". This netname
  646. contains three items that serve to insure it is unique. Going
  647. backwards, there is only one naming domain called "sun.com" in the
  648. internet. Within this domain, there is only one UNIX user with
  649. user ID 515. However, there may be another user on another
  650. operating system, for example VMS, within the same naming domain
  651. that, by coincidence, happens to have the same user ID. To insure
  652. that these two users can be distinguished we add the operating
  653. system name. So one user is "unix.515@sun.com" and the other is
  654. "vms.515@sun.com".
  655. .LP
  656. The first field is actually a naming method rather than an
  657. operating system name. It just happens that today there is almost
  658. a one-to-one correspondence between naming methods and operating
  659. systems. If the world could agree on a naming standard, the first
  660. field could be the name of that standard, instead of an operating
  661. system name.
  662. .LP
  663. .NH 3
  664. \&DES Authentication Verifiers
  665. .LP
  666. Unlike UNIX authentication, DES authentication does have a verifier
  667. so the server can validate the client's credential (and
  668. vice-versa). The contents of this verifier is primarily an
  669. encrypted timestamp. The server can decrypt this timestamp, and if
  670. it is close to what the real time is, then the client must have
  671. encrypted it correctly. The only way the client could encrypt it
  672. correctly is to know the "conversation key" of the RPC session. And
  673. if the client knows the conversation key, then it must be the real
  674. client.
  675. .LP
  676. The conversation key is a DES [5] key which the client generates
  677. and notifies the server of in its first RPC call. The conversation
  678. key is encrypted using a public key scheme in this first
  679. transaction. The particular public key scheme used in DES
  680. authentication is Diffie-Hellman [3] with 192-bit keys. The
  681. details of this encryption method are described later.
  682. .LP
  683. The client and the server need the same notion of the current time
  684. in order for all of this to work. If network time synchronization
  685. cannot be guaranteed, then client can synchronize with the server
  686. before beginning the conversation, perhaps by consulting the
  687. Internet Time Server (TIME[4]).
  688. .LP
  689. The way a server determines if a client timestamp is valid is
  690. somewhat complicated. For any other transaction but the first, the
  691. server just checks for two things:
  692. .IP 1.
  693. the timestamp is greater than the one previously seen from the
  694. same client.
  695. .IP 2.
  696. the timestamp has not expired.
  697. .LP
  698. A timestamp is expired if the server's time is later than the sum
  699. of the client's timestamp plus what is known as the client's
  700. "window". The "window" is a number the client passes (encrypted)
  701. to the server in its first transaction. You can think of it as a
  702. lifetime for the credential.
  703. .LP
  704. This explains everything but the first transaction. In the first
  705. transaction, the server checks only that the timestamp has not
  706. expired. If this was all that was done though, then it would be
  707. quite easy for the client to send random data in place of the
  708. timestamp with a fairly good chance of succeeding. As an added
  709. check, the client sends an encrypted item in the first transaction
  710. known as the "window verifier" which must be equal to the window
  711. minus 1, or the server will reject the credential.
  712. .LP
  713. The client too must check the verifier returned from the server to
  714. be sure it is legitimate. The server sends back to the client the
  715. encrypted timestamp it received from the client, minus one second.
  716. If the client gets anything different than this, it will reject it.
  717. .LP
  718. .NH 3
  719. \&Nicknames and Clock Synchronization
  720. .LP
  721. After the first transaction, the server's DES authentication
  722. subsystem returns in its verifier to the client an integer
  723. "nickname" which the client may use in its further transactions
  724. instead of passing its netname, encrypted DES key and window every
  725. time. The nickname is most likely an index into a table on the
  726. server which stores for each client its netname, decrypted DES key
  727. and window.
  728. .LP
  729. Though they originally were synchronized, the client's and server's
  730. clocks can get out of sync again. When this happens the client RPC
  731. subsystem most likely will get back
  732. .I RPC_AUTHERROR
  733. at which point it should resynchronize.
  734. .LP
  735. A client may still get the
  736. .I RPC_AUTHERROR
  737. error even though it is
  738. synchronized with the server. The reason is that the server's
  739. nickname table is a limited size, and it may flush entries whenever
  740. it wants. A client should resend its original credential in this
  741. case and the server will give it a new nickname. If a server
  742. crashes, the entire nickname table gets flushed, and all clients
  743. will have to resend their original credentials.
  744. .KS
  745. .NH 3
  746. \&DES Authentication Protocol (in XDR language)
  747. .ie t .DS
  748. .el .DS L
  749. .ft I
  750. /*
  751. * There are two kinds of credentials: one in which the client uses
  752. * its full network name, and one in which it uses its "nickname"
  753. * (just an unsigned integer) given to it by the server. The
  754. * client must use its fullname in its first transaction with the
  755. * server, in which the server will return to the client its
  756. * nickname. The client may use its nickname in all further
  757. * transactions with the server. There is no requirement to use the
  758. * nickname, but it is wise to use it for performance reasons.
  759. */
  760. .ft CW
  761. enum authdes_namekind {
  762. ADN_FULLNAME = 0,
  763. ADN_NICKNAME = 1
  764. };
  765. .ft I
  766. /*
  767. * A 64-bit block of encrypted DES data
  768. */
  769. .ft CW
  770. typedef opaque des_block[8];
  771. .ft I
  772. /*
  773. * Maximum length of a network user's name
  774. */
  775. .ft CW
  776. const MAXNETNAMELEN = 255;
  777. .ft I
  778. /*
  779. * A fullname contains the network name of the client, an encrypted
  780. * conversation key and the window. The window is actually a
  781. * lifetime for the credential. If the time indicated in the
  782. * verifier timestamp plus the window has past, then the server
  783. * should expire the request and not grant it. To insure that
  784. * requests are not replayed, the server should insist that
  785. * timestamps are greater than the previous one seen, unless it is
  786. * the first transaction. In the first transaction, the server
  787. * checks instead that the window verifier is one less than the
  788. * window.
  789. */
  790. .ft CW
  791. struct authdes_fullname {
  792. string name<MAXNETNAMELEN>; /* \fIname of client \f(CW*/
  793. des_block key; /* \fIPK encrypted conversation key \f(CW*/
  794. unsigned int window; /* \fIencrypted window \f(CW*/
  795. };
  796. .ft I
  797. /*
  798. * A credential is either a fullname or a nickname
  799. */
  800. .ft CW
  801. union authdes_cred switch (authdes_namekind adc_namekind) {
  802. case ADN_FULLNAME:
  803. authdes_fullname adc_fullname;
  804. case ADN_NICKNAME:
  805. unsigned int adc_nickname;
  806. };
  807. .ft I
  808. /*
  809. * A timestamp encodes the time since midnight, January 1, 1970.
  810. */
  811. .ft CW
  812. struct timestamp {
  813. unsigned int seconds; /* \fIseconds \fP*/
  814. unsigned int useconds; /* \fIand microseconds \fP*/
  815. };
  816. .ft I
  817. /*
  818. * Verifier: client variety
  819. * The window verifier is only used in the first transaction. In
  820. * conjunction with a fullname credential, these items are packed
  821. * into the following structure before being encrypted:
  822. *
  823. * \f(CWstruct {\fP
  824. * \f(CWadv_timestamp; \fP-- one DES block
  825. * \f(CWadc_fullname.window; \fP-- one half DES block
  826. * \f(CWadv_winverf; \fP-- one half DES block
  827. * \f(CW}\fP
  828. * This structure is encrypted using CBC mode encryption with an
  829. * input vector of zero. All other encryptions of timestamps use
  830. * ECB mode encryption.
  831. */
  832. .ft CW
  833. struct authdes_verf_clnt {
  834. timestamp adv_timestamp; /* \fIencrypted timestamp \fP*/
  835. unsigned int adv_winverf; /* \fIencrypted window verifier \fP*/
  836. };
  837. .ft I
  838. /*
  839. * Verifier: server variety
  840. * The server returns (encrypted) the same timestamp the client
  841. * gave it minus one second. It also tells the client its nickname
  842. * to be used in future transactions (unencrypted).
  843. */
  844. .ft CW
  845. struct authdes_verf_svr {
  846. timestamp adv_timeverf; /* \fIencrypted verifier \fP*/
  847. unsigned int adv_nickname; /* \fInew nickname for client \fP*/
  848. };
  849. .DE
  850. .KE
  851. .NH 3
  852. \&Diffie-Hellman Encryption
  853. .LP
  854. In this scheme, there are two constants,
  855. .I BASE
  856. and
  857. .I MODULUS .
  858. The
  859. particular values Sun has chosen for these for the DES
  860. authentication protocol are:
  861. .ie t .DS
  862. .el .DS L
  863. .ft CW
  864. const BASE = 3;
  865. const MODULUS =
  866. "d4a0ba0250b6fd2ec626e7efd637df76c716e22d0944b88b"; /* \fIhex \fP*/
  867. .DE
  868. .ft R
  869. The way this scheme works is best explained by an example. Suppose
  870. there are two people "A" and "B" who want to send encrypted
  871. messages to each other. So, A and B both generate "secret" keys at
  872. random which they do not reveal to anyone. Let these keys be
  873. represented as SK(A) and SK(B). They also publish in a public
  874. directory their "public" keys. These keys are computed as follows:
  875. .ie t .DS
  876. .el .DS L
  877. .ft CW
  878. PK(A) = ( BASE ** SK(A) ) mod MODULUS
  879. PK(B) = ( BASE ** SK(B) ) mod MODULUS
  880. .DE
  881. .ft R
  882. The "**" notation is used here to represent exponentiation. Now,
  883. both A and B can arrive at the "common" key between them,
  884. represented here as CK(A, B), without revealing their secret keys.
  885. .LP
  886. A computes:
  887. .ie t .DS
  888. .el .DS L
  889. .ft CW
  890. CK(A, B) = ( PK(B) ** SK(A)) mod MODULUS
  891. .DE
  892. .ft R
  893. while B computes:
  894. .ie t .DS
  895. .el .DS L
  896. .ft CW
  897. CK(A, B) = ( PK(A) ** SK(B)) mod MODULUS
  898. .DE
  899. .ft R
  900. These two can be shown to be equivalent:
  901. .ie t .DS
  902. .el .DS L
  903. .ft CW
  904. (PK(B) ** SK(A)) mod MODULUS = (PK(A) ** SK(B)) mod MODULUS
  905. .DE
  906. .ft R
  907. We drop the "mod MODULUS" parts and assume modulo arithmetic to
  908. simplify things:
  909. .ie t .DS
  910. .el .DS L
  911. .ft CW
  912. PK(B) ** SK(A) = PK(A) ** SK(B)
  913. .DE
  914. .ft R
  915. Then, replace PK(B) by what B computed earlier and likewise for
  916. PK(A).
  917. .ie t .DS
  918. .el .DS L
  919. .ft CW
  920. ((BASE ** SK(B)) ** SK(A) = (BASE ** SK(A)) ** SK(B)
  921. .DE
  922. .ft R
  923. which leads to:
  924. .ie t .DS
  925. .el .DS L
  926. .ft CW
  927. BASE ** (SK(A) * SK(B)) = BASE ** (SK(A) * SK(B))
  928. .DE
  929. .ft R
  930. This common key CK(A, B) is not used to encrypt the timestamps used
  931. in the protocol. Rather, it is used only to encrypt a conversation
  932. key which is then used to encrypt the timestamps. The reason for
  933. doing this is to use the common key as little as possible, for fear
  934. that it could be broken. Breaking the conversation key is a far
  935. less serious offense, since conversations are relatively
  936. short-lived.
  937. .LP
  938. The conversation key is encrypted using 56-bit DES keys, yet the
  939. common key is 192 bits. To reduce the number of bits, 56 bits are
  940. selected from the common key as follows. The middle-most 8-bytes
  941. are selected from the common key, and then parity is added to the
  942. lower order bit of each byte, producing a 56-bit key with 8 bits of
  943. parity.
  944. .KS
  945. .NH 1
  946. \&Record Marking Standard
  947. .LP
  948. When RPC messages are passed on top of a byte stream protocol (like
  949. TCP/IP), it is necessary, or at least desirable, to delimit one
  950. message from another in order to detect and possibly recover from
  951. user protocol errors. This is called record marking (RM). Sun uses
  952. this RM/TCP/IP transport for passing RPC messages on TCP streams.
  953. One RPC message fits into one RM record.
  954. .LP
  955. A record is composed of one or more record fragments. A record
  956. fragment is a four-byte header followed by 0 to (2**31) - 1 bytes of
  957. fragment data. The bytes encode an unsigned binary number; as with
  958. XDR integers, the byte order is from highest to lowest. The number
  959. encodes two values\(ema boolean which indicates whether the fragment
  960. is the last fragment of the record (bit value 1 implies the fragment
  961. is the last fragment) and a 31-bit unsigned binary value which is the
  962. length in bytes of the fragment's data. The boolean value is the
  963. highest-order bit of the header; the length is the 31 low-order bits.
  964. (Note that this record specification is NOT in XDR standard form!)
  965. .KE
  966. .KS
  967. .NH 1
  968. \&The RPC Language
  969. .LP
  970. Just as there was a need to describe the XDR data-types in a formal
  971. language, there is also need to describe the procedures that operate
  972. on these XDR data-types in a formal language as well. We use the RPC
  973. Language for this purpose. It is an extension to the XDR language.
  974. The following example is used to describe the essence of the
  975. language.
  976. .NH 2
  977. \&An Example Service Described in the RPC Language
  978. .LP
  979. Here is an example of the specification of a simple ping program.
  980. .ie t .DS
  981. .el .DS L
  982. .vs 11
  983. .ft I
  984. /*
  985. * Simple ping program
  986. */
  987. .ft CW
  988. program PING_PROG {
  989. /* \fILatest and greatest version\fP */
  990. version PING_VERS_PINGBACK {
  991. void
  992. PINGPROC_NULL(void) = 0;
  993. .ft I
  994. /*
  995. * Ping the caller, return the round-trip time
  996. * (in microseconds). Returns -1 if the operation
  997. * timed out.
  998. */
  999. .ft CW
  1000. int
  1001. PINGPROC_PINGBACK(void) = 1;
  1002. } = 2;
  1003. .ft I
  1004. /*
  1005. * Original version
  1006. */
  1007. .ft CW
  1008. version PING_VERS_ORIG {
  1009. void
  1010. PINGPROC_NULL(void) = 0;
  1011. } = 1;
  1012. } = 1;
  1013. const PING_VERS = 2; /* \fIlatest version \fP*/
  1014. .vs
  1015. .DE
  1016. .KE
  1017. .LP
  1018. The first version described is
  1019. .I PING_VERS_PINGBACK
  1020. with two procedures,
  1021. .I PINGPROC_NULL
  1022. and
  1023. .I PINGPROC_PINGBACK .
  1024. .I PINGPROC_NULL
  1025. takes no arguments and returns no results, but it is useful for
  1026. computing round-trip times from the client to the server and back
  1027. again. By convention, procedure 0 of any RPC protocol should have
  1028. the same semantics, and never require any kind of authentication.
  1029. The second procedure is used for the client to have the server do a
  1030. reverse ping operation back to the client, and it returns the amount
  1031. of time (in microseconds) that the operation used. The next version,
  1032. .I PING_VERS_ORIG ,
  1033. is the original version of the protocol
  1034. and it does not contain
  1035. .I PINGPROC_PINGBACK
  1036. procedure. It is useful
  1037. for compatibility with old client programs, and as this program
  1038. matures it may be dropped from the protocol entirely.
  1039. .KS
  1040. .NH 2
  1041. \&The RPC Language Specification
  1042. .LP
  1043. The RPC language is identical to the XDR language, except for the
  1044. added definition of a
  1045. .I program-def
  1046. described below.
  1047. .DS
  1048. .ft CW
  1049. program-def:
  1050. "program" identifier "{"
  1051. version-def
  1052. version-def *
  1053. "}" "=" constant ";"
  1054. version-def:
  1055. "version" identifier "{"
  1056. procedure-def
  1057. procedure-def *
  1058. "}" "=" constant ";"
  1059. procedure-def:
  1060. type-specifier identifier "(" type-specifier ")"
  1061. "=" constant ";"
  1062. .DE
  1063. .KE
  1064. .NH 2
  1065. \&Syntax Notes
  1066. .IP 1.
  1067. The following keywords are added and cannot be used as
  1068. identifiers: "program" and "version";
  1069. .IP 2.
  1070. A version name cannot occur more than once within the scope of
  1071. a program definition. Nor can a version number occur more than once
  1072. within the scope of a program definition.
  1073. .IP 3.
  1074. A procedure name cannot occur more than once within the scope
  1075. of a version definition. Nor can a procedure number occur more than
  1076. once within the scope of version definition.
  1077. .IP 4.
  1078. Program identifiers are in the same name space as constant and
  1079. type identifiers.
  1080. .IP 5.
  1081. Only unsigned constants can be assigned to programs, versions
  1082. and procedures.
  1083. .NH 1
  1084. \&Port Mapper Program Protocol
  1085. .LP
  1086. The port mapper program maps RPC program and version numbers to
  1087. transport-specific port numbers. This program makes dynamic binding
  1088. of remote programs possible.
  1089. .LP
  1090. This is desirable because the range of reserved port numbers is very
  1091. small and the number of potential remote programs is very large. By
  1092. running only the port mapper on a reserved port, the port numbers of
  1093. other remote programs can be ascertained by querying the port mapper.
  1094. .LP
  1095. The port mapper also aids in broadcast RPC. A given RPC program will
  1096. usually have different port number bindings on different machines, so
  1097. there is no way to directly broadcast to all of these programs. The
  1098. port mapper, however, does have a fixed port number. So, to
  1099. broadcast to a given program, the client actually sends its message
  1100. to the port mapper located at the broadcast address. Each port
  1101. mapper that picks up the broadcast then calls the local service
  1102. specified by the client. When the port mapper gets the reply from
  1103. the local service, it sends the reply on back to the client.
  1104. .KS
  1105. .NH 2
  1106. \&Port Mapper Protocol Specification (in RPC Language)
  1107. .ie t .DS
  1108. .el .DS L
  1109. .ft CW
  1110. .vs 11
  1111. const PMAP_PORT = 111; /* \fIportmapper port number \fP*/
  1112. .ft I
  1113. /*
  1114. * A mapping of (program, version, protocol) to port number
  1115. */
  1116. .ft CW
  1117. struct mapping {
  1118. unsigned int prog;
  1119. unsigned int vers;
  1120. unsigned int prot;
  1121. unsigned int port;
  1122. };
  1123. .ft I
  1124. /*
  1125. * Supported values for the "prot" field
  1126. */
  1127. .ft CW
  1128. const IPPROTO_TCP = 6; /* \fIprotocol number for TCP/IP \fP*/
  1129. const IPPROTO_UDP = 17; /* \fIprotocol number for UDP/IP \fP*/
  1130. .ft I
  1131. /*
  1132. * A list of mappings
  1133. */
  1134. .ft CW
  1135. struct *pmaplist {
  1136. mapping map;
  1137. pmaplist next;
  1138. };
  1139. .vs
  1140. .DE
  1141. .ie t .DS
  1142. .el .DS L
  1143. .vs 11
  1144. .ft I
  1145. /*
  1146. * Arguments to callit
  1147. */
  1148. .ft CW
  1149. struct call_args {
  1150. unsigned int prog;
  1151. unsigned int vers;
  1152. unsigned int proc;
  1153. opaque args<>;
  1154. };
  1155. .ft I
  1156. /*
  1157. * Results of callit
  1158. */
  1159. .ft CW
  1160. struct call_result {
  1161. unsigned int port;
  1162. opaque res<>;
  1163. };
  1164. .vs
  1165. .DE
  1166. .KE
  1167. .ie t .DS
  1168. .el .DS L
  1169. .vs 11
  1170. .ft I
  1171. /*
  1172. * Port mapper procedures
  1173. */
  1174. .ft CW
  1175. program PMAP_PROG {
  1176. version PMAP_VERS {
  1177. void
  1178. PMAPPROC_NULL(void) = 0;
  1179. bool
  1180. PMAPPROC_SET(mapping) = 1;
  1181. bool
  1182. PMAPPROC_UNSET(mapping) = 2;
  1183. unsigned int
  1184. PMAPPROC_GETPORT(mapping) = 3;
  1185. pmaplist
  1186. PMAPPROC_DUMP(void) = 4;
  1187. call_result
  1188. PMAPPROC_CALLIT(call_args) = 5;
  1189. } = 2;
  1190. } = 100000;
  1191. .vs
  1192. .DE
  1193. .NH 2
  1194. \&Port Mapper Operation
  1195. .LP
  1196. The portmapper program currently supports two protocols (UDP/IP and
  1197. TCP/IP). The portmapper is contacted by talking to it on assigned
  1198. port number 111 (SUNRPC [8]) on either of these protocols. The
  1199. following is a description of each of the portmapper procedures:
  1200. .IP \fBPMAPPROC_NULL:\fP
  1201. This procedure does no work. By convention, procedure zero of any
  1202. protocol takes no parameters and returns no results.
  1203. .IP \fBPMAPPROC_SET:\fP
  1204. When a program first becomes available on a machine, it registers
  1205. itself with the port mapper program on the same machine. The program
  1206. passes its program number "prog", version number "vers", transport
  1207. protocol number "prot", and the port "port" on which it awaits
  1208. service request. The procedure returns a boolean response whose
  1209. value is
  1210. .I TRUE
  1211. if the procedure successfully established the mapping and
  1212. .I FALSE
  1213. otherwise. The procedure refuses to establish
  1214. a mapping if one already exists for the tuple "(prog, vers, prot)".
  1215. .IP \fBPMAPPROC_UNSET:\fP
  1216. When a program becomes unavailable, it should unregister itself with
  1217. the port mapper program on the same machine. The parameters and
  1218. results have meanings identical to those of
  1219. .I PMAPPROC_SET .
  1220. The protocol and port number fields of the argument are ignored.
  1221. .IP \fBPMAPPROC_GETPORT:\fP
  1222. Given a program number "prog", version number "vers", and transport
  1223. protocol number "prot", this procedure returns the port number on
  1224. which the program is awaiting call requests. A port value of zeros
  1225. means the program has not been registered. The "port" field of the
  1226. argument is ignored.
  1227. .IP \fBPMAPPROC_DUMP:\fP
  1228. This procedure enumerates all entries in the port mapper's database.
  1229. The procedure takes no parameters and returns a list of program,
  1230. version, protocol, and port values.
  1231. .IP \fBPMAPPROC_CALLIT:\fP
  1232. This procedure allows a caller to call another remote procedure on
  1233. the same machine without knowing the remote procedure's port number.
  1234. It is intended for supporting broadcasts to arbitrary remote programs
  1235. via the well-known port mapper's port. The parameters "prog",
  1236. "vers", "proc", and the bytes of "args" are the program number,
  1237. version number, procedure number, and parameters of the remote
  1238. procedure.
  1239. .LP
  1240. .B Note:
  1241. .RS
  1242. .IP 1.
  1243. This procedure only sends a response if the procedure was
  1244. successfully executed and is silent (no response) otherwise.
  1245. .IP 2.
  1246. The port mapper communicates with the remote program using UDP/IP
  1247. only.
  1248. .RE
  1249. .LP
  1250. The procedure returns the remote program's port number, and the bytes
  1251. of results are the results of the remote procedure.
  1252. .bp
  1253. .NH 1
  1254. \&References
  1255. .LP
  1256. [1] Birrell, Andrew D. & Nelson, Bruce Jay; "Implementing Remote
  1257. Procedure Calls"; XEROX CSL-83-7, October 1983.
  1258. .LP
  1259. [2] Cheriton, D.; "VMTP: Versatile Message Transaction Protocol",
  1260. Preliminary Version 0.3; Stanford University, January 1987.
  1261. .LP
  1262. [3] Diffie & Hellman; "New Directions in Cryptography"; IEEE
  1263. Transactions on Information Theory IT-22, November 1976.
  1264. .LP
  1265. [4] Harrenstien, K.; "Time Server", RFC 738; Information Sciences
  1266. Institute, October 1977.
  1267. .LP
  1268. [5] National Bureau of Standards; "Data Encryption Standard"; Federal
  1269. Information Processing Standards Publication 46, January 1977.
  1270. .LP
  1271. [6] Postel, J.; "Transmission Control Protocol - DARPA Internet
  1272. Program Protocol Specification", RFC 793; Information Sciences
  1273. Institute, September 1981.
  1274. .LP
  1275. [7] Postel, J.; "User Datagram Protocol", RFC 768; Information Sciences
  1276. Institute, August 1980.
  1277. .LP
  1278. [8] Reynolds, J. & Postel, J.; "Assigned Numbers", RFC 923; Information
  1279. Sciences Institute, October 1984.