scripts/extract-module-sig.pl

   1 #!/usr/bin/perl -w
   2 #
   3 # extract-mod-sig <part> <module-file>
   4 #
   5 # Reads the module file and writes out some or all of the signature
   6 # section to stdout.  Part is the bit to be written and is one of:
   7 #
   8 #  -0: The unsigned module, no signature data at all
   9 #  -a: All of the signature data, including magic number
  10 #  -d: Just the descriptor values as a sequence of numbers
  11 #  -n: Just the signer's name
  12 #  -k: Just the key ID
  13 #  -s: Just the crypto signature or PKCS#7 message
  14 #
  15 use strict;
  16
  17 die "Format: $0 -[0adnks] module-file >out\n"
  18     if ($#ARGV != 1);
  19
  20 my $part = $ARGV[0];
  21 my $modfile = $ARGV[1];
  22
  23 my $magic_number = "~Module signature appended~\n";
  24
  25 #
  26 # Read the module contents
  27 #
  28 open FD, "<$modfile" || die $modfile;
  29 binmode(FD);
  30 my @st = stat(FD);
  31 die "$modfile" unless (@st);
  32 my $buf = "";
  33 my $len = sysread(FD, $buf, $st[7]);
  34 die "$modfile" unless (defined($len));
  35 die "Short read on $modfile\n" unless ($len == $st[7]);
  36 close(FD) || die $modfile;
  37
  38 print STDERR "Read ", $len, " bytes from module file\n";
  39
  40 die "The file is too short to have a sig magic number and descriptor\n"
  41     if ($len < 12 + length($magic_number));
  42
  43 #
  44 # Check for the magic number and extract the information block
  45 #
  46 my $p = $len - length($magic_number);
  47 my $raw_magic = substr($buf, $p);
  48
  49 die "Magic number not found at $len\n"
  50     if ($raw_magic ne $magic_number);
  51 print STDERR "Found magic number at $len\n";
  52
  53 $p -= 12;
  54 my $raw_info = substr($buf, $p, 12);
  55
  56 my @info = unpack("CCCCCxxxN", $raw_info);
  57 my ($algo, $hash, $id_type, $name_len, $kid_len, $sig_len) = @info;
  58
  59 if ($id_type == 0) {
  60     print STDERR "Found PGP key identifier\n";
  61 } elsif ($id_type == 1) {
  62     print STDERR "Found X.509 cert identifier\n";
  63 } elsif ($id_type == 2) {
  64     print STDERR "Found PKCS#7/CMS encapsulation\n";
  65 } else {
  66     print STDERR "Found unsupported identifier type $id_type\n";
  67 }
  68
  69 #
  70 # Extract the three pieces of info data
  71 #
  72 die "Insufficient name+kid+sig data in file\n"
  73     unless ($p >= $name_len + $kid_len + $sig_len);
  74
  75 $p -= $sig_len;
  76 my $raw_sig = substr($buf, $p, $sig_len);
  77 $p -= $kid_len;
  78 my $raw_kid = substr($buf, $p, $kid_len);
  79 $p -= $name_len;
  80 my $raw_name = substr($buf, $p, $name_len);
  81
  82 my $module_len = $p;
  83
  84 if ($sig_len > 0) {
  85     print STDERR "Found $sig_len bytes of signature [";
  86     my $n = $sig_len > 16 ? 16 : $sig_len;
  87     foreach my $i (unpack("C" x $n, substr($raw_sig, 0, $n))) {
  88         printf STDERR "%02x", $i;
  89     }
  90     print STDERR "]\n";
  91 }
  92
  93 if ($kid_len > 0) {
  94     print STDERR "Found $kid_len bytes of key identifier [";
  95     my $n = $kid_len > 16 ? 16 : $kid_len;
  96     foreach my $i (unpack("C" x $n, substr($raw_kid, 0, $n))) {
  97         printf STDERR "%02x", $i;
  98     }
  99     print STDERR "]\n";
 100 }
 101
 102 if ($name_len > 0) {
 103     print STDERR "Found $name_len bytes of signer's name [$raw_name]\n";
 104 }
 105
 106 #
 107 # Produce the requested output
 108 #
 109 if ($part eq "-0") {
 110     # The unsigned module, no signature data at all
 111     binmode(STDOUT);
 112     print substr($buf, 0, $module_len);
 113 } elsif ($part eq "-a") {
 114     # All of the signature data, including magic number
 115     binmode(STDOUT);
 116     print substr($buf, $module_len);
 117 } elsif ($part eq "-d") {
 118     # Just the descriptor values as a sequence of numbers
 119     print join(" ", @info), "\n";
 120 } elsif ($part eq "-n") {
 121     # Just the signer's name
 122     print STDERR "No signer's name for PKCS#7 message type sig\n"
 123         if ($id_type == 2);
 124     binmode(STDOUT);
 125     print $raw_name;
 126 } elsif ($part eq "-k") {
 127     # Just the key identifier
 128     print STDERR "No key ID for PKCS#7 message type sig\n"
 129         if ($id_type == 2);
 130     binmode(STDOUT);
 131     print $raw_kid;
 132 } elsif ($part eq "-s") {
 133     # Just the crypto signature or PKCS#7 message
 134     binmode(STDOUT);
 135     print $raw_sig;
 136 }