Secure Shell Working Group                                  J. Galbraith
Internet-Draft                                          VanDyke Software
Expires: October 4, 2004                                       R. Thayer
                                                     The Tillerman Group
                                                           April 5, 2004


                       SSH Public Key File Format
                 draft-ietf-secsh-publickeyfile-05.txt

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on October 4, 2004.

Copyright Notice

   Copyright (C) The Internet Society (2004). All Rights Reserved.

Abstract

   This document formally documents the existing public key file format
   in use for exchanging public keys between different SSH
   implementations.











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Table of Contents

   1.  Conventions used in this document  . . . . . . . . . . . . . .  3
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Key File Format  . . . . . . . . . . . . . . . . . . . . . . .  5
     3.1   Line termination Characters  . . . . . . . . . . . . . . .  5
     3.2   Begin and end markers  . . . . . . . . . . . . . . . . . .  5
     3.3   Key File Header  . . . . . . . . . . . . . . . . . . . . .  5
       3.3.1   Subject Header . . . . . . . . . . . . . . . . . . . .  6
       3.3.2   Comment Header . . . . . . . . . . . . . . . . . . . .  6
     3.4   Public Key File Body . . . . . . . . . . . . . . . . . . .  6
     3.5   Examples . . . . . . . . . . . . . . . . . . . . . . . . .  7
   4.  Security Considerations  . . . . . . . . . . . . . . . . . . .  8
   5.  Normative References . . . . . . . . . . . . . . . . . . . . .  8
       Authors' Addresses . . . . . . . . . . . . . . . . . . . . . .  9
       Intellectual Property and Copyright Statements . . . . . . . . 10



































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1.  Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [4].














































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2.  Introduction

   In order to use public key authentication, public keys must be
   exchanged between client and server.  This document formally
   describes the existing public key file format, with few exceptions.

   Where this document departs from current practice, it also suggests a
   mechanism for backwards compatibility.











































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3.  Key File Format

   SSH implementations must share public key files between the client
   and the server in order to interoperate.

   A key file is a text file, containing a sequence of lines. Each line
   in the file MUST NOT be longer than 72 bytes.

3.1  Line termination Characters

   In order to achieve the goal of being able to exchange public key
   files between servers, implementations are REQUIRED to read files
   using any of the common line termination sequence, <CR>, <LF> or
   <CR><LF>.

   Implementations may generate files using which ever line termination
   convention is most convenient

3.2  Begin and end markers

   The first line of a conforming key file MUST be a begin marker, which
   is the literal text:

   ---- BEGIN SSH2 PUBLIC KEY ----

   The last line of a conforming key file MUST be a end marker, which is
   the literal text:

   ---- END SSH2 PUBLIC KEY ----

3.3  Key File Header

   The key file header section consists of multiple RFC822 - style
   header fields.  Each field is a line of the following format:

   Header-tag ':' ' ' Header-value

   The Header-tag MUST NOT be more than 64 bytes.  The Header-value MUST
   NOT be more than 1024 bytes.  Each line in the header MUST NOT be
   more than 72 bytes.

   A line is continued if the last character in the line is a '\'.  If
   the last character of a line is a '\', then the logical contents of
   the line is formed by removing the '\' and appending the contents of
   the next line.

   The Header-tag MUST be US-ASCII.  The Header-value MUST be encoded in
   UTF-8. [2]



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   A line that is not a continuation line that has no ':' in it is
   assumed to be the first line of the base 64 encoded body (Section 8)

   Compliant implementations MUST ignore unrecognized header fields.
   Implementations SHOULD preserve unrecognized header fields when
   manipulating the key file.

   Existing implementations may not correctly handle unrecognized
   fields. During a transition period, implementations SHOULD generate
   key file headers that contain only a Subject field followed by a
   Comment field.

3.3.1  Subject Header

   This field currently is used to store the login-name that the key was
   generated under.  For example:

   Subject: user

3.3.2  Comment Header

   Contain a user specified comment which will be displayed when using
   the key.

   It is suggested that this field default to user@hostname for the user
   and machine used to generate the key.  For example:

   Comment: user@mycompany.com

   Currently, common practice is to quote the Header-value of the
   Comment, and some existing implementations fail if these quotes are
   omitted.

   Compliant implementations MUST function correctly if the quotes are
   omitted.

   During an interim period implementations MAY include the quotes. If
   the first and last characters of the Header-value are matching
   quotes, implementations SHOULD remove them before using the value.

3.4  Public Key File Body

   The body of a public key file consists of the public key blob as
   described in the SSH transport draft [1], section 4.6, "Public Key
   Algorithms", encoded in base 64 as specified in RFC-2045, section 
   6.8, "Base64 Content-Transfer-Encoding". [5]

   As with all other lines, each line in the body MUST NOT be longer



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   than 72 characters.

3.5  Examples

   The following are some example public key files that are compliant:

        ---- BEGIN SSH2 PUBLIC KEY ----
        Comment: "1024-bit RSA, converted from OpenSSH by galb@test1"
        AAAAB3NzaC1yc2EAAAABIwAAAIEA1on8gxCGJJWSRT4uOrR13mUaUk0hRf4RzxSZ1zRbYY
        Fw8pfGesIFoEuVth4HKyF8k1y4mRUnYHP1XNMNMJl1JcEArC2asV8sHf6zSPVffozZ5TT4
        SfsUu/iKy9lUcCfXzwre4WWZSXXcPff+EHtWshahu3WzBdnGxm5Xoi89zcE=
        ---- END SSH2 PUBLIC KEY ----


        ---- BEGIN SSH2 PUBLIC KEY ----
        Comment: DSA Public Key for use with MyIsp
        AAAAB3NzaC1kc3MAAACBAPY8ZOHY2yFSJA6XYC9HRwNHxaehvx5wOJ0rzZdzoSOXxbETW6
        ToHv8D1UJ/z+zHo9Fiko5XybZnDIaBDHtblQ+Yp7StxyltHnXF1YLfKD1G4T6JYrdHYI14
        Om1eg9e4NnCRleaqoZPF3UGfZia6bXrGTQf3gJq2e7Yisk/gF+1VAAAAFQDb8D5cvwHWTZ
        DPfX0D2s9Rd7NBvQAAAIEAlN92+Bb7D4KLYk3IwRbXblwXdkPggA4pfdtW9vGfJ0/RHd+N
        jB4eo1D+0dix6tXwYGN7PKS5R/FXPNwxHPapcj9uL1Jn2AWQ2dsknf+i/FAAvioUPkmdMc
        0zuWoSOEsSNhVDtX3WdvVcGcBq9cetzrtOKWOocJmJ80qadxTRHtUAAACBAN7CY+KKv1gH
        pRzFwdQm7HK9bb1LAo2KwaoXnadFgeptNBQeSXG1vO+JsvphVMBJc9HSn24VYtYtsMu74q
        XviYjziVucWKjjKEb11juqnF0GDlB3VVmxHLmxnAz643WK42Z7dLM5sY29ouezv4Xz2PuM
        ch5VGPP+CDqzCM4loWgV
        ---- END SSH2 PUBLIC KEY ----


        ---- BEGIN SSH2 PUBLIC KEY ----
        Subject: galb
        Comment: 1024-bit rsa, created by galb@shimi Mon Jan 15 08:31:24 2001
        AAAAB3NzaC1yc2EAAAABJQAAAIEAiPWx6WM4lhHNedGfBpPJNPpZ7yKu+dnn1SJejgt459
        6k6YjzGGphH2TUxwKzxcKDKKezwkpfnxPkSMkuEspGRt/aZZ9wa++Oi7Qkr8prgHc4soW6
        NUlfDzpvZK2H5E7eQaSeP3SAwGmQKUFHCddNaP0L+hM7zhFNzjFvpaMgJw0=
        ---- END SSH2 PUBLIC KEY ----
















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4.  Security Considerations

   The file format described by this document provides no mechanism to
   verify the integrity or otherwise detect tampering with the data
   stored in such files. Given the potential of an adversarial tampering
   with this data, system-specific measures (e.g. Access Control Lists,
   UNIX permissions, other Discretionary and/or Mandatory Access
   Controls) SHOULD be used to protect these files. Also, if the
   contents of these files are transferred it SHOULD be done over a
   trusted channel.

   The header data allowed by this file format could contain an
   unlimited range of information. While in many environments the
   information conveyed by this header data may be considered innocuous
   public information, it may constitute a channel through which
   information about a user, a key or its use may be disclosed
   intentionally or otherwise (e.g "Comment: Mary E. Jones, 123 Main St,
   Home Phone:..."). The presence and use of this header data SHOULD be
   reviewed by sites that deploy this file format.

5  Normative References

   [1]  Rinne, T., Ylonen, T., Kivinen, T., Saarinen, M. and S.
        Lehtinen, "SSH Protocol Transport Protocol", September 2002.

   [2]  Yergeau, F., "UTF-8, a Transformation Format of Unicode and ISO
        10646", October 1996.

   [3]  Bradner, S., "The Internet Standards Process -- Revision 3",
        October 1996.

   [4]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", March 1997.

   [5]  Freed and Borenstein, "Multipurpose Internet Mail Extensions
        (MIME) Part One: Format of Internet Message Bodies", November
        1996.














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Authors' Addresses

   Joseph Galbraith
   VanDyke Software
   4848 Tramway Ridge Blvd
   Suite 101
   Albuquerque, NM  87111
   US

   Phone: +1 505 332 5700
   EMail: galb-list@vandyke.com


   Rodney Thayer
   The Tillerman Group
   370 Altair Way, PMB 321
   Sunnyvale, CA  94086

   Phone: +1 408 757 9693
   EMail: rodney@tillerman.to































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Intellectual Property Statement

   The IETF takes no position regarding the validity or scope of any
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   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
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Acknowledgment

   Funding for the RFC Editor function is currently provided by the
   Internet Society.











































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