KEYS: Provide a script to extract a module signature
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>
diff --git a/scripts/extract-module-sig.pl b/scripts/extract-module-sig.pl
new file mode 100755
index 0000000..faac6f2
--- /dev/null
+++ b/scripts/extract-module-sig.pl
@@ -0,0 +1,136 @@
+#!/usr/bin/perl -w
+#
+# extract-mod-sig <part> <module-file>
+#
+# Reads the module file and writes out some or all of the signature
+# section to stdout. Part is the bit to be written and is one of:
+#
+# -0: The unsigned module, no signature data at all
+# -a: All of the signature data, including magic number
+# -d: Just the descriptor values as a sequence of numbers
+# -n: Just the signer's name
+# -k: Just the key ID
+# -s: Just the crypto signature or PKCS#7 message
+#
+use strict;
+
+die "Format: $0 -[0adnks] module-file >out\n"
+ if ($#ARGV != 1);
+
+my $part = $ARGV[0];
+my $modfile = $ARGV[1];
+
+my $magic_number = "~Module signature appended~\n";
+
+#
+# Read the module contents
+#
+open FD, "<$modfile" || die $modfile;
+binmode(FD);
+my @st = stat(FD);
+die "$modfile" unless (@st);
+my $buf = "";
+my $len = sysread(FD, $buf, $st[7]);
+die "$modfile" unless (defined($len));
+die "Short read on $modfile\n" unless ($len == $st[7]);
+close(FD) || die $modfile;
+
+print STDERR "Read ", $len, " bytes from module file\n";
+
+die "The file is too short to have a sig magic number and descriptor\n"
+ if ($len < 12 + length($magic_number));
+
+#
+# Check for the magic number and extract the information block
+#
+my $p = $len - length($magic_number);
+my $raw_magic = substr($buf, $p);
+
+die "Magic number not found at $len\n"
+ if ($raw_magic ne $magic_number);
+print STDERR "Found magic number at $len\n";
+
+$p -= 12;
+my $raw_info = substr($buf, $p, 12);
+
+my @info = unpack("CCCCCxxxN", $raw_info);
+my ($algo, $hash, $id_type, $name_len, $kid_len, $sig_len) = @info;
+
+if ($id_type == 0) {
+ print STDERR "Found PGP key identifier\n";
+} elsif ($id_type == 1) {
+ print STDERR "Found X.509 cert identifier\n";
+} elsif ($id_type == 2) {
+ print STDERR "Found PKCS#7/CMS encapsulation\n";
+} else {
+ print STDERR "Found unsupported identifier type $id_type\n";
+}
+
+#
+# Extract the three pieces of info data
+#
+die "Insufficient name+kid+sig data in file\n"
+ unless ($p >= $name_len + $kid_len + $sig_len);
+
+$p -= $sig_len;
+my $raw_sig = substr($buf, $p, $sig_len);
+$p -= $kid_len;
+my $raw_kid = substr($buf, $p, $kid_len);
+$p -= $name_len;
+my $raw_name = substr($buf, $p, $name_len);
+
+my $module_len = $p;
+
+if ($sig_len > 0) {
+ print STDERR "Found $sig_len bytes of signature [";
+ my $n = $sig_len > 16 ? 16 : $sig_len;
+ foreach my $i (unpack("C" x $n, substr($raw_sig, 0, $n))) {
+ printf STDERR "%02x", $i;
+ }
+ print STDERR "]\n";
+}
+
+if ($kid_len > 0) {
+ print STDERR "Found $kid_len bytes of key identifier [";
+ my $n = $kid_len > 16 ? 16 : $kid_len;
+ foreach my $i (unpack("C" x $n, substr($raw_kid, 0, $n))) {
+ printf STDERR "%02x", $i;
+ }
+ print STDERR "]\n";
+}
+
+if ($name_len > 0) {
+ print STDERR "Found $name_len bytes of signer's name [$raw_name]\n";
+}
+
+#
+# Produce the requested output
+#
+if ($part eq "-0") {
+ # The unsigned module, no signature data at all
+ binmode(STDOUT);
+ print substr($buf, 0, $module_len);
+} elsif ($part eq "-a") {
+ # All of the signature data, including magic number
+ binmode(STDOUT);
+ print substr($buf, $module_len);
+} elsif ($part eq "-d") {
+ # Just the descriptor values as a sequence of numbers
+ print join(" ", @info), "\n";
+} elsif ($part eq "-n") {
+ # Just the signer's name
+ print STDERR "No signer's name for PKCS#7 message type sig\n"
+ if ($id_type == 2);
+ binmode(STDOUT);
+ print $raw_name;
+} elsif ($part eq "-k") {
+ # Just the key identifier
+ print STDERR "No key ID for PKCS#7 message type sig\n"
+ if ($id_type == 2);
+ binmode(STDOUT);
+ print $raw_kid;
+} elsif ($part eq "-s") {
+ # Just the crypto signature or PKCS#7 message
+ binmode(STDOUT);
+ print $raw_sig;
+}