📄 draft-ietf-secsh-architecture-15.2.ps
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5 129 M(Ylonen & Moffat Expires March 31, 2004 [Page 4]) s_RSPStoPSsaved restore%%Page: (4,5) 3userdict/PStoPSsaved save putPStoPSmatrix setmatrix595.000000 0.271378 translate90 rotate0.706651 dup scaleuserdict/PStoPSmatrix matrix currentmatrix putuserdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip/showpage{}def/copypage{}def/erasepage{}defPStoPSxform concat%%BeginPageSetup_S75 0 translate/pagenum 5 def/fname () def/fdir () def/ftail () def/user_header_p false def%%EndPageSetup5 723 M(Internet-Draft SSH Protocol Architecture Oct 2003) s5 690 M( connections to that host.) s5 668 M( Implementations MAY provide additional methods for verifying the) s5 657 M( correctness of host keys, e.g. a hexadecimal fingerprint derived from) s5 646 M( the SHA-1 hash of the public key. Such fingerprints can easily be) s5 635 M( verified by using telephone or other external communication channels.) s5 613 M( All implementations SHOULD provide an option to not accept host keys) s5 602 M( that cannot be verified.) s5 580 M( We believe that ease of use is critical to end-user acceptance of) s5 569 M( security solutions, and no improvement in security is gained if the) s5 558 M( new solutions are not used. Thus, providing the option not to check) s5 547 M( the server host key is believed to improve the overall security of) s5 536 M( the Internet, even though it reduces the security of the protocol in) s5 525 M( configurations where it is allowed.) s5 503 M(4.2 Extensibility) s5 481 M( We believe that the protocol will evolve over time, and some) s5 470 M( organizations will want to use their own encryption, authentication) s5 459 M( and/or key exchange methods. Central registration of all extensions) s5 448 M( is cumbersome, especially for experimental or classified features.) s5 437 M( On the other hand, having no central registration leads to conflicts) s5 426 M( in method identifiers, making interoperability difficult.) s5 404 M( We have chosen to identify algorithms, methods, formats, and) s5 393 M( extension protocols with textual names that are of a specific format.) s5 382 M( DNS names are used to create local namespaces where experimental or) s5 371 M( classified extensions can be defined without fear of conflicts with) s5 360 M( other implementations.) s5 338 M( One design goal has been to keep the base protocol as simple as) s5 327 M( possible, and to require as few algorithms as possible. However, all) s5 316 M( implementations MUST support a minimal set of algorithms to ensure) s5 305 M( interoperability \(this does not imply that the local policy on all) s5 294 M( hosts would necessary allow these algorithms\). The mandatory) s5 283 M( algorithms are specified in the relevant protocol documents.) s5 261 M( Additional algorithms, methods, formats, and extension protocols can) s5 250 M( be defined in separate drafts. See Section Algorithm Naming \(Section) s5 239 M( 6\) for more information.) s5 217 M(4.3 Policy Issues) s5 195 M( The protocol allows full negotiation of encryption, integrity, key) s5 184 M( exchange, compression, and public key algorithms and formats.) s5 173 M( Encryption, integrity, public key, and compression algorithms can be) s5 129 M(Ylonen & Moffat Expires March 31, 2004 [Page 5]) s_RSPStoPSsaved restoreuserdict/PStoPSsaved save putPStoPSmatrix setmatrix595.000000 421.271378 translate90 rotate0.706651 dup scaleuserdict/PStoPSmatrix matrix currentmatrix putuserdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclipPStoPSxform concat%%BeginPageSetup_S75 0 translate/pagenum 6 def/fname () def/fdir () def/ftail () def/user_header_p false def%%EndPageSetup5 723 M(Internet-Draft SSH Protocol Architecture Oct 2003) s5 690 M( different for each direction.) s5 668 M( The following policy issues SHOULD be addressed in the configuration) s5 657 M( mechanisms of each implementation:) s5 646 M( o Encryption, integrity, and compression algorithms, separately for) s5 635 M( each direction. The policy MUST specify which is the preferred) s5 624 M( algorithm \(e.g. the first algorithm listed in each category\).) s5 613 M( o Public key algorithms and key exchange method to be used for host) s5 602 M( authentication. The existence of trusted host keys for different) s5 591 M( public key algorithms also affects this choice.) s5 580 M( o The authentication methods that are to be required by the server) s5 569 M( for each user. The server's policy MAY require multiple) s5 558 M( authentication for some or all users. The required algorithms MAY) s5 547 M( depend on the location where the user is trying to log in from.) s5 536 M( o The operations that the user is allowed to perform using the) s5 525 M( connection protocol. Some issues are related to security; for) s5 514 M( example, the policy SHOULD NOT allow the server to start sessions) s5 503 M( or run commands on the client machine, and MUST NOT allow) s5 492 M( connections to the authentication agent unless forwarding such) s5 481 M( connections has been requested. Other issues, such as which TCP/) s5 470 M( IP ports can be forwarded and by whom, are clearly issues of local) s5 459 M( policy. Many of these issues may involve traversing or bypassing) s5 448 M( firewalls, and are interrelated with the local security policy.) s5 426 M(4.4 Security Properties) s5 404 M( The primary goal of the SSH protocol is improved security on the) s5 393 M( Internet. It attempts to do this in a way that is easy to deploy,) s5 382 M( even at the cost of absolute security.) s5 371 M( o All encryption, integrity, and public key algorithms used are) s5 360 M( well-known, well-established algorithms.) s5 349 M( o All algorithms are used with cryptographically sound key sizes) s5 338 M( that are believed to provide protection against even the strongest) s5 327 M( cryptanalytic attacks for decades.) s5 316 M( o All algorithms are negotiated, and in case some algorithm is) s5 305 M( broken, it is easy to switch to some other algorithm without) s5 294 M( modifying the base protocol.) s5 272 M( Specific concessions were made to make wide-spread fast deployment) s5 261 M( easier. The particular case where this comes up is verifying that) s5 250 M( the server host key really belongs to the desired host; the protocol) s5 239 M( allows the verification to be left out \(but this is NOT RECOMMENDED\).) s5 228 M( This is believed to significantly improve usability in the short) s5 217 M( term, until widespread Internet public key infrastructures emerge.) s5 195 M(4.5 Packet Size and Overhead) s5 173 M( Some readers will worry about the increase in packet size due to new) s5 129 M(Ylonen & Moffat Expires March 31, 2004 [Page 6]) s_RSPStoPSsaved restore%%Page: (6,7) 4userdict/PStoPSsaved save putPStoPSmatrix setmatrix595.000000 0.271378 translate90 rotate0.706651 dup scaleuserdict/PStoPSmatrix matrix currentmatrix putuserdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclip/showpage{}def/copypage{}def/erasepage{}defPStoPSxform concat%%BeginPageSetup_S75 0 translate/pagenum 7 def/fname () def/fdir () def/ftail () def/user_header_p false def%%EndPageSetup5 723 M(Internet-Draft SSH Protocol Architecture Oct 2003) s5 690 M( headers, padding, and MAC. The minimum packet size is in the order) s5 679 M( of 28 bytes \(depending on negotiated algorithms\). The increase is) s5 668 M( negligible for large packets, but very significant for one-byte) s5 657 M( packets \(telnet-type sessions\). There are, however, several factors) s5 646 M( that make this a non-issue in almost all cases:) s5 635 M( o The minimum size of a TCP/IP header is 32 bytes. Thus, the) s5 624 M( increase is actually from 33 to 51 bytes \(roughly\).) s5 613 M( o The minimum size of the data field of an Ethernet packet is 46) s5 602 M( bytes [RFC-894]. Thus, the increase is no more than 5 bytes. When) s5 591 M( Ethernet headers are considered, the increase is less than 10) s5 580 M( percent.) s5 569 M( o The total fraction of telnet-type data in the Internet is) s5 558 M( negligible, even with increased packet sizes.) s5 536 M( The only environment where the packet size increase is likely to have) s5 525 M( a significant effect is PPP [RFC-1134] over slow modem lines \(PPP) s5 514 M( compresses the TCP/IP headers, emphasizing the increase in packet) s5 503 M( size\). However, with modern modems, the time needed to transfer is in) s5 492 M( the order of 2 milliseconds, which is a lot faster than people can) s5 481 M( type.) s5 459 M( There are also issues related to the maximum packet size. To) s5 448 M( minimize delays in screen updates, one does not want excessively) s5 437 M( large packets for interactive sessions. The maximum packet size is) s5 426 M( negotiated separately for each channel.) s5 404 M(4.6 Localization and Character Set Support) s5 382 M( For the most part, the SSH protocols do not directly pass text that) s5 371 M( would be displayed to the user. However, there are some places where) s5 360 M( such data might be passed. When applicable, the character set for the) s5 349 M( data MUST be explicitly specified. In most places, ISO 10646 with) s5 338 M( UTF-8 encoding is used [RFC-2279]. When applicable, a field is also) s5 327 M( provided for a language tag [RFC-3066].) s5 305 M( One big issue is the character set of the interactive session. There) s5 294 M( is no clear solution, as different applications may display data in) s5 283 M( different formats. Different types of terminal emulation may also be) s5 272 M( employed in the client, and the character set to be used is) s5 261 M( effectively determined by the terminal emulation. Thus, no place is) s5 250 M( provided for directly specifying the character set or encoding for) s5 239 M( terminal session data. However, the terminal emulation type \(e.g.) s5 228 M( "vt100"\) is transmitted to the remote site, and it implicitly) s5 217 M( specifies the character set and encoding. Applications typically use) s5 206 M( the terminal type to determine what character set they use, or the) s5 195 M( character set is determined using some external means. The terminal) s5 184 M( emulation may also allow configuring the default character set. In) s5 173 M( any case, the character set for the terminal session is considered) s5 129 M(Ylonen & Moffat Expires March 31, 2004 [Page 7]) s_RSPStoPSsaved restoreuserdict/PStoPSsaved save putPStoPSmatrix setmatrix595.000000 421.271378 translate90 rotate0.706651 dup scaleuserdict/PStoPSmatrix matrix currentmatrix putuserdict/PStoPSclip{0 0 moveto 595.000000 0 rlineto 0 842.000000 rlineto -595.000000 0 rlineto closepath}put initclipPStoPSxform concat%%BeginPageSetup_S75 0 translate/pagenum 8 def/fname () def/fdir () def/ftail () def/user_header_p false def%%EndPageSetup5 723 M(Internet-Draft SSH Protocol Architecture Oct 2003) s5 690 M( primarily a client local issue.) s5 668 M( Internal names used to identify algorithms or protocols are normally) s5 657 M( never displayed to users, and must be in US-ASCII.) s5 635 M( The client and server user names are inherently constrained by what) s5 624 M( the server is prepared to accept. They might, however, occasionally) s5 613 M( be displayed in logs, reports, etc. They MUST be encoded using ISO) s5 602 M( 10646 UTF-8, but other encodings may be required in some cases. It) s5 591 M( is up to the server to decide how to map user names to accepted user) s5 580 M( names. Straight bit-wise binary comparison is RECOMMENDED.) s5 558 M( For localization purposes, the protocol attempts to minimize the) s5 547 M( number of textual messages transmitted. When present, such messages) s5 536 M( typically relate to errors, debugging information, or some externally) s5 525 M( configured data. For data that is normally displayed, it SHOULD be) s5 514 M( possible to fetch a localized message instead of the transmitted) s5 503 M( message by using a numerical code. The remaining messages SHOULD be) s5 492 M( configurable.) s5 470 M(5. Data Type Representations Used in the SSH Protocols) s5 459 M( byte) s5 437 M( A byte represents an arbitrary 8-bit value \(octet\) [RFC-1700].) s5 426 M( Fixed length data is sometimes represented as an array of bytes,) s5 415 M( written byte[n], where n is the number of bytes in the array.) s5 393 M( boolean) s5 371 M( A boolean value is stored as a single byte. The value 0) s5 360 M( represents FALSE, and the value 1 represents TRUE. All non-zero) s5 349 M( values MUST be interpreted as TRUE; however, applications MUST NOT) s5 338 M( store values other than 0 and 1.) s5 316 M( uint32) s5 294 M⌨️ 快捷键说明
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