4adc605edc
The supplied script takes a signed module file and extracts the tailmost
signature (there could theoretically be more than one) and dumps all or
part of it or the unsigned file to stdout.
Call as:
scripts/extract-module-sig.pl -[0adnks] module-file >out
where the initial flag indicates which bit of the signed file you want dumping
to stdout:
(*) "-0". Dumps the unsigned data with the signature stripped.
(*) "-a". Dumps all of the signature data, including the magic number.
(*) "-d". Dumps the signature information block as a sequence of decimal
numbers in text form with spaces between (crypto algorithm type,
hash type, identifier type, signer's name length, key identifier
length and signature length).
(*) "-n". Dumps the signer's name contents.
(*) "-k". Dumps the key identifier contents.
(*) "-s". Dumps the cryptographic signature contents.
In the case that the signature is a PKCS#7 (or CMS) message, -n and -k will
print a warning to stderr and dump nothing to stdout, but will otherwise
complete okay; the entire PKCS#7/CMS message will be dumped by "-s"; and "-d"
will show "0 0 2 0 0 <pkcs#7-msg-len>".
Signed-off-by: David Howells <dhowells@redhat.com>
136 lines
3.6 KiB
Perl
Executable file
136 lines
3.6 KiB
Perl
Executable file
#!/usr/bin/perl -w
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#
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# extract-mod-sig <part> <module-file>
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#
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# Reads the module file and writes out some or all of the signature
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# section to stdout. Part is the bit to be written and is one of:
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#
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# -0: The unsigned module, no signature data at all
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# -a: All of the signature data, including magic number
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# -d: Just the descriptor values as a sequence of numbers
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# -n: Just the signer's name
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# -k: Just the key ID
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# -s: Just the crypto signature or PKCS#7 message
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#
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use strict;
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die "Format: $0 -[0adnks] module-file >out\n"
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if ($#ARGV != 1);
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my $part = $ARGV[0];
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my $modfile = $ARGV[1];
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my $magic_number = "~Module signature appended~\n";
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#
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# Read the module contents
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#
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open FD, "<$modfile" || die $modfile;
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binmode(FD);
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my @st = stat(FD);
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die "$modfile" unless (@st);
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my $buf = "";
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my $len = sysread(FD, $buf, $st[7]);
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die "$modfile" unless (defined($len));
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die "Short read on $modfile\n" unless ($len == $st[7]);
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close(FD) || die $modfile;
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print STDERR "Read ", $len, " bytes from module file\n";
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die "The file is too short to have a sig magic number and descriptor\n"
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if ($len < 12 + length($magic_number));
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#
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# Check for the magic number and extract the information block
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#
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my $p = $len - length($magic_number);
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my $raw_magic = substr($buf, $p);
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die "Magic number not found at $len\n"
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if ($raw_magic ne $magic_number);
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print STDERR "Found magic number at $len\n";
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$p -= 12;
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my $raw_info = substr($buf, $p, 12);
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my @info = unpack("CCCCCxxxN", $raw_info);
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my ($algo, $hash, $id_type, $name_len, $kid_len, $sig_len) = @info;
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if ($id_type == 0) {
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print STDERR "Found PGP key identifier\n";
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} elsif ($id_type == 1) {
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print STDERR "Found X.509 cert identifier\n";
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} elsif ($id_type == 2) {
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print STDERR "Found PKCS#7/CMS encapsulation\n";
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} else {
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print STDERR "Found unsupported identifier type $id_type\n";
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}
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#
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# Extract the three pieces of info data
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#
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die "Insufficient name+kid+sig data in file\n"
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unless ($p >= $name_len + $kid_len + $sig_len);
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$p -= $sig_len;
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my $raw_sig = substr($buf, $p, $sig_len);
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$p -= $kid_len;
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my $raw_kid = substr($buf, $p, $kid_len);
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$p -= $name_len;
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my $raw_name = substr($buf, $p, $name_len);
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my $module_len = $p;
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if ($sig_len > 0) {
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print STDERR "Found $sig_len bytes of signature [";
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my $n = $sig_len > 16 ? 16 : $sig_len;
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foreach my $i (unpack("C" x $n, substr($raw_sig, 0, $n))) {
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printf STDERR "%02x", $i;
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}
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print STDERR "]\n";
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}
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if ($kid_len > 0) {
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print STDERR "Found $kid_len bytes of key identifier [";
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my $n = $kid_len > 16 ? 16 : $kid_len;
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foreach my $i (unpack("C" x $n, substr($raw_kid, 0, $n))) {
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printf STDERR "%02x", $i;
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}
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print STDERR "]\n";
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}
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if ($name_len > 0) {
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print STDERR "Found $name_len bytes of signer's name [$raw_name]\n";
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}
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#
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# Produce the requested output
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#
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if ($part eq "-0") {
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# The unsigned module, no signature data at all
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binmode(STDOUT);
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print substr($buf, 0, $module_len);
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} elsif ($part eq "-a") {
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# All of the signature data, including magic number
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binmode(STDOUT);
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print substr($buf, $module_len);
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} elsif ($part eq "-d") {
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# Just the descriptor values as a sequence of numbers
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print join(" ", @info), "\n";
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} elsif ($part eq "-n") {
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# Just the signer's name
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print STDERR "No signer's name for PKCS#7 message type sig\n"
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if ($id_type == 2);
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binmode(STDOUT);
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print $raw_name;
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} elsif ($part eq "-k") {
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# Just the key identifier
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print STDERR "No key ID for PKCS#7 message type sig\n"
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if ($id_type == 2);
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binmode(STDOUT);
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print $raw_kid;
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} elsif ($part eq "-s") {
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# Just the crypto signature or PKCS#7 message
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binmode(STDOUT);
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print $raw_sig;
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}
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