1、外文文献原文 SMTP Service Extension for Authentication This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the Internet Official Protocol Standards (STD 1) for the standard
2、ization state and status of this protocol. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (1999). All Rights Reserved. 1. Introduction This document defines an SMTP service extension ESMTP whereby an SMTP client may indicate an authentication mechanism to
3、 the server,perform an authentication protocol exchange, and optionally negotiatea security layer for subsequent protocol interactions. This extension is a profile of the Simple Authentication and Security Layer SASL. 2. Conventions Used in this Document In examples, C: and S: indicate lines sent by
4、 the client and server respectively. The key words MUST, MUST NOT, SHOULD, SHOULD NOT, and MAY in this document are to be interpreted as defined in Key words for use in RFCs to Indicate Requirement Levels KEYWORDS. 3. The Authentication service extension (1) the name of the SMTP service extension is
5、 Authentication (2) the EHLO keyword value associated with this extension is AUTH (3) The AUTH EHLO keyword contains as a parameter a space separated list of the names of supported SASL mechanisms. (4) a new SMTP verb AUTH is defined (5) an optional parameter using the keyword AUTH is added to the M
6、AIL FROM command, and extends the maximum line length of the MAIL FROM command by 500 characters. (6) this extension is appropriate for the submission protocol SUBMIT. 4. The AUTH command AUTH mechanism initial-response Arguments: a string identifying a SASL authentication mechanism. an optional bas
7、e64-encoded response Restrictions: After an AUTH command has successfully completed, no more AUTH commands may be issued in the same session. After a successful AUTH command completes, a server MUST reject any further AUTH commands with a 503 reply. The AUTH command is not permitted during a mail tr
8、ansaction. Discussion: The AUTH command indicates an authentication mechanism to the server. If the server supports the requested authentication mechanism, it performs an authentication protocol exchange to authenticate and identify the user. Optionally, it also negotiates a security layer for subse
9、quent protocol interactions. If the requested authentication mechanism is not supported, the server rejects the AUTH command with a 504 reply. The authentication protocol exchange consists of a series of server challenges and client answers that are specific to the authentication mechanism. A server
10、 challenge, otherwise known as a ready response, is a 334 reply with the text part containing a BASE64 encoded string. The client answer consists of a line containing a BASE64 encoded string. If the client wishes to cancel an authentication exchange, it issues a line with a single *. If the server r
11、eceives such an answer, it MUST reject the AUTH command by sending a 501 reply. The optional initial-response argument to the AUTH command is used to save a round trip when using authentication mechanisms that are defined to send no data in the initial challenge. When the initial-response argument i
12、s used with such a mechanism, the initial empty challenge is not sent to the client and the server uses the data in the initial-response argument as if it were sent in response to the empty challenge. Unlike a zero-length client answer to a 334 reply, a zero- length initial response is sent as a sin
13、gle equals sign (=). If the client uses an initial-response argument to the AUTH command with a mechanism that sends data in the initial challenge, the server rejects the AUTH command with a 535 reply. If the server cannot BASE64 decode the argument, it rejects the AUTH command with a 501 reply. If
14、the server rejects the authentication data, it SHOULD reject the AUTH command with a 535 reply unless a more specific error code, such as one listed in section 6, is appropriate. Should the client successfully complete the authentication exchange, the SMTP server issues a 235 reply. The service name
15、 specified by this protocols profile of SASL is smtp. If a security layer is negotiated through the SASL authentication exchange, it takes effect immediately following the CRLF that concludes the authentication exchange for the client, and the CRLF of the success reply for the server. Upon a securit
16、y layers taking effect, the SMTP protocol is reset to the initial state (the state in SMTP after a server issues a 220 service ready greeting). The server MUST discard any knowledge obtained from the client, such as the argument to the EHLO command, which was not obtained from the SASL negotiation i
17、tself. The client MUST discard any knowledge obtained from the server, such as the list of SMTP service extensions, which was not obtained from the SASL negotiation itself (with the exception that a client MAY compare the list of advertised SASL mechanisms before and after authentication in order to
18、 detect an active down-negotiation attack). The client SHOULD send an EHLO command as the first command after a successful SASL negotiation which results in the enabling of a security layer. The server is not required to support any particular authentication mechanism, nor are authentication mechani
19、sms required to support any security layers. If an AUTH command fails, the client may try another authentication mechanism by issuing another AUTH command. If an AUTH command fails, the server MUST behave the same as if the client had not issued the AUTH command. The BASE64 string may in general be arbitrarily long. Clients and servers MUST be able to support challenges and responses that are as long as are generated by the authentication mechanisms they support, independent of any line length limitations the client or server may have in other parts of its protocol implementation. Examples:
