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Linux/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 }

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