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6. Algorithm and Method Naming

  1. Algorithm and Method Naming

The SSH protocols refer to particular hash, encryption, integrity, compression, and key exchange algorithms or methods by name. There are some standard algorithms and methods that all implementations MUST support. There are also algorithms and methods that are defined in the protocol specification, but are OPTIONAL. Furthermore, it is expected that some organizations will want to use their own algorithms or methods.

In this protocol, all algorithm and method identifiers MUST be printable US-ASCII, non-empty strings no longer than 64 characters. Names MUST be case-sensitive.

RFC 4251 SSH Protocol Architecture January 2006

There are two formats for algorithm and method names:

o Names that do not contain an at-sign ("@") are reserved to be assigned by IETF CONSENSUS. Examples include "3des-cbc", "sha-1", "hmac-sha1", and "zlib" (the doublequotes are not part of the name). Names of this format are only valid if they are first registered with the IANA. Registered names MUST NOT contain an at-sign ("@"), comma (","), whitespace, control characters (ASCII codes 32 or less), or the ASCII code 127 (DEL). Names are case- sensitive, and MUST NOT be longer than 64 characters.

o Anyone can define additional algorithms or methods by using names in the format name@domainname, e.g., "[email protected]". The format of the part preceding the at-sign is not specified; however, these names MUST be printable US-ASCII strings, and MUST NOT contain the comma character (","), whitespace, control characters (ASCII codes 32 or less), or the ASCII code 127 (DEL). They MUST have only a single at-sign in them. The part following the at-sign MUST be a valid, fully qualified domain name [RFC1034] controlled by the person or organization defining the name. Names are case-sensitive, and MUST NOT be longer than 64 characters. It is up to each domain how it manages its local namespace. It should be noted that these names resemble STD 11 [RFC0822] email addresses. This is purely coincidental and has nothing to do with STD 11 [RFC0822].

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