Girocco/SSHUtil.pm

   1 # Girocco::SSHUtil.pm -- OpenSSH public key utility
   2 # Copyright (c) 2013 Kyle J. McKay.  All rights reserved.
   3
   4 # This program is free software; you can redistribute it and/or
   5 # modify it under the terms of the GNU General Public License
   6 # as published by the Free Software Foundation; either version 2
   7 # of the License, or (at your option) any later version.
   8 #
   9 # This program is distributed in the hope that it will be useful,
  10 # but WITHOUT ANY WARRANTY; without even the implied warranty of
  11 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12 # GNU General Public License for more details.
  13 #
  14 # You should have received a copy of the GNU General Public License
  15 # along with this program; if not, write to the Free Software
  16 # Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  17
  18 package Girocco::SSHUtil;
  19
  20 use strict;
  21 use warnings;
  22
  23 use base qw(Exporter);
  24 our @EXPORT;
  25 our $VERSION;
  26
  27 BEGIN {
  28         @EXPORT = qw(sshpub_validate);
  29         *VERSION = \'1.0';
  30 }
  31
  32 use MIME::Base64;
  33 use Digest::MD5 qw(md5_hex);
  34
  35 # Input: binary sequence of one or more 4-byte big-endian length + contents
  36 #        sequences
  37 # Output: array of contents or () if invalid
  38 sub _splitparts($)
  39 {
  40         my $data = shift;
  41         my @parts = ();
  42         while (length($data) >= 4) {
  43                 my $len = unpack('N',substr($data,0,4));
  44                 my $value = '';
  45                 if ($len > 0) {
  46                         return () if $len + 4 > length($data);
  47                         $value = substr($data,4,$len);
  48                 }
  49                 push(@parts, $value);
  50                 substr($data, 0, 4+$len) = '';
  51         }
  52         return () unless length($data) == 0;
  53         return @parts;
  54 }
  55
  56 # Input: binary key data
  57 # Output: how many key bits are present
  58 sub _countbits($)
  59 {
  60         my $data = shift;
  61         return undef if length($data) < 1;
  62         my $bits = 8 * length($data);
  63         # but leading zero bits must be subtracted
  64         my $byte = unpack('C',substr($data,0,1));
  65         if (!$byte) {
  66                 $bits -= 8;
  67         } else {
  68                 return undef if $byte & 0x80; # negative is not valid
  69                 while (!($byte & 0x80)) {
  70                         --$bits;
  71                         $byte <<= 1;
  72                 }
  73         }
  74         return $bits;
  75 }
  76
  77 # sshpub_validate
  78 #   Input: A single-line ssh public key such as the contents of id_rsa.pub
  79 #   Output:
  80 #     () (if invalid key)
  81 #     -OR-
  82 #     array of 4 elements:
  83 #       key type (either 'ssh-dss' or 'ssh-rsa')
  84 #       key size (integer such as 1024, 2048, 3072, 4096 etc.)
  85 #       key fingerprint (string as shown by ssh-keygen -l -E md5)
  86 #       key comment (may be '' if none)
  87 sub sshpub_validate($)
  88 {
  89         my $raw = shift;
  90         return () if !$raw;
  91         my @fields = split(/[ ]/, $raw, 3);
  92         return () if @fields < 2;
  93         return () if $fields[0] ne 'ssh-dss' && $fields[0] ne 'ssh-rsa';
  94         return () if $fields[1] !~ m,^[0-9A-Za-z+/=]+$,;
  95         $fields[2] = '' if !$fields[2];
  96         $fields[2] = join(' ', split(' ', $fields[2]));
  97         my $data = decode_base64($fields[1]);
  98         return () if !$data || length($data) < 21;
  99         my @parts = _splitparts($data);
 100         return () if @parts < 3 || $parts[0] ne $fields[0];
 101         # ssh-rsa is 3 fields: type, e, n
 102         # ssh-dss is 5 fields: type, p, q, g, y
 103         my $bitlength;
 104         if ($parts[0] eq 'ssh-dss') {
 105                 return () if @parts != 5;
 106                 $bitlength = _countbits($parts[1]);
 107         } elsif ($parts[0] eq 'ssh-rsa') {
 108                 return () if @parts != 3;
 109                 $bitlength = _countbits($parts[2]);
 110         } else {
 111                 return ();
 112         }
 113         return () if !$bitlength || $bitlength < 512; # probably should be 2048
 114         my $fingerprint = md5_hex($data);
 115         $fingerprint =~ s/(..)(?=.)/$1:/g;
 116         return ($fields[0], $bitlength, $fingerprint, $fields[2]);
 117 }
 118
 119 1;