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linux/scripts/x509keyid
David Howells 85ecac7945 MODSIGN: Provide a script for generating a key ID from an X.509 cert 
Provide a script to parse an X.509 certificate and certain pieces of
information from it in order to generate a key identifier to be included within
a module signature.

The script takes the Subject Name and extracts (if present) the
organizationName (O), the commonName (CN) and the emailAddress and fabricates
the signer's name from them:

 (1) If both O and CN exist, then the name will be "O: CN", unless:

     (a) CN is prefixed by O, in which case only CN is used.

     (b) CN and O share at least the first 7 characters, in which case only CN
     	 is used.

 (2) Otherwise, CN is used if present.

 (3) Otherwise, O is used if present.

 (4) Otherwise the emailAddress is used, if present.

 (5) Otherwise a blank name is used.

The script emits a binary encoded identifier in the following form:

 - 2 BE bytes indicating the length of the signer's name.

 - 2 BE bytes indicating the length of the subject key identifier.

 - The characters of the signer's name.

 - The bytes of the subject key identifier.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
2012-10-10 20:06:33 +10:30

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8.0 KiB
Perl
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#!/usr/bin/perl -w
#
# Generate an identifier from an X.509 certificate that can be placed in a
# module signature to indentify the key to use.
#
# Format:
#
# ./scripts/x509keyid <x509-cert> <signer's-name> <key-id>
#
# We read the DER-encoded X509 certificate and parse it to extract the Subject
# name and Subject Key Identifier. The provide the data we need to build the
# certificate identifier.
#
# The signer's name part of the identifier is fabricated from the commonName,
# the organizationName or the emailAddress components of the X.509 subject
# name and written to the second named file.
#
# The subject key ID to select which of that signer's certificates we're
# intending to use to sign the module is written to the third named file.
#
use strict;
my $raw_data;
die "Need three filenames\n" if ($#ARGV != 2);
my $src = $ARGV[0];
open(FD, "<$src") || die $src;
binmode FD;
my @st = stat(FD);
die $src if (!@st);
read(FD, $raw_data, $st[7]) || die $src;
close(FD);
my $UNIV = 0 << 6;
my $APPL = 1 << 6;
my $CONT = 2 << 6;
my $PRIV = 3 << 6;
my $CONS = 0x20;
my $BOOLEAN = 0x01;
my $INTEGER = 0x02;
my $BIT_STRING = 0x03;
my $OCTET_STRING = 0x04;
my $NULL = 0x05;
my $OBJ_ID = 0x06;
my $UTF8String = 0x0c;
my $SEQUENCE = 0x10;
my $SET = 0x11;
my $UTCTime = 0x17;
my $GeneralizedTime = 0x18;
my %OIDs = (
pack("CCC", 85, 4, 3) => "commonName",
pack("CCC", 85, 4, 6) => "countryName",
pack("CCC", 85, 4, 10) => "organizationName",
pack("CCC", 85, 4, 11) => "organizationUnitName",
pack("CCCCCCCCC", 42, 134, 72, 134, 247, 13, 1, 1, 1) => "rsaEncryption",
pack("CCCCCCCCC", 42, 134, 72, 134, 247, 13, 1, 1, 5) => "sha1WithRSAEncryption",
pack("CCCCCCCCC", 42, 134, 72, 134, 247, 13, 1, 9, 1) => "emailAddress",
pack("CCC", 85, 29, 35) => "authorityKeyIdentifier",
pack("CCC", 85, 29, 14) => "subjectKeyIdentifier",
pack("CCC", 85, 29, 19) => "basicConstraints"
);
###############################################################################
#
# Extract an ASN.1 element from a string and return information about it.
#
###############################################################################
sub asn1_extract($$@)
{
my ($cursor, $expected_tag, $optional) = @_;
return [ -1 ]
if ($cursor->[1] == 0 && $optional);
die $src, ": ", $cursor->[0], ": ASN.1 data underrun (elem ", $cursor->[1], ")\n"
if ($cursor->[1] < 2);
my ($tag, $len) = unpack("CC", substr(${$cursor->[2]}, $cursor->[0], 2));
if ($expected_tag != -1 && $tag != $expected_tag) {
return [ -1 ]
if ($optional);
die $src, ": ", $cursor->[0], ": ASN.1 unexpected tag (", $tag,
" not ", $expected_tag, ")\n";
}
$cursor->[0] += 2;
$cursor->[1] -= 2;
die $src, ": ", $cursor->[0], ": ASN.1 long tag\n"
if (($tag & 0x1f) == 0x1f);
die $src, ": ", $cursor->[0], ": ASN.1 indefinite length\n"
if ($len == 0x80);
if ($len > 0x80) {
my $l = $len - 0x80;
die $src, ": ", $cursor->[0], ": ASN.1 data underrun (len len $l)\n"
if ($cursor->[1] < $l);
if ($l == 0x1) {
$len = unpack("C", substr(${$cursor->[2]}, $cursor->[0], 1));
} elsif ($l = 0x2) {
$len = unpack("n", substr(${$cursor->[2]}, $cursor->[0], 2));
} elsif ($l = 0x3) {
$len = unpack("C", substr(${$cursor->[2]}, $cursor->[0], 1)) << 16;
$len = unpack("n", substr(${$cursor->[2]}, $cursor->[0] + 1, 2));
} elsif ($l = 0x4) {
$len = unpack("N", substr(${$cursor->[2]}, $cursor->[0], 4));
} else {
die $src, ": ", $cursor->[0], ": ASN.1 element too long (", $l, ")\n";
}
$cursor->[0] += $l;
$cursor->[1] -= $l;
}
die $src, ": ", $cursor->[0], ": ASN.1 data underrun (", $len, ")\n"
if ($cursor->[1] < $len);
my $ret = [ $tag, [ $cursor->[0], $len, $cursor->[2] ] ];
$cursor->[0] += $len;
$cursor->[1] -= $len;
return $ret;
}
###############################################################################
#
# Retrieve the data referred to by a cursor
#
###############################################################################
sub asn1_retrieve($)
{
my ($cursor) = @_;
my ($offset, $len, $data) = @$cursor;
return substr($$data, $offset, $len);
}
###############################################################################
#
# Roughly parse the X.509 certificate
#
###############################################################################
my $cursor = [ 0, length($raw_data), \$raw_data ];
my $cert = asn1_extract($cursor, $UNIV | $CONS | $SEQUENCE);
my $tbs = asn1_extract($cert->[1], $UNIV | $CONS | $SEQUENCE);
my $version = asn1_extract($tbs->[1], $CONT | $CONS | 0, 1);
my $serial_number = asn1_extract($tbs->[1], $UNIV | $INTEGER);
my $sig_type = asn1_extract($tbs->[1], $UNIV | $CONS | $SEQUENCE);
my $issuer = asn1_extract($tbs->[1], $UNIV | $CONS | $SEQUENCE);
my $validity = asn1_extract($tbs->[1], $UNIV | $CONS | $SEQUENCE);
my $subject = asn1_extract($tbs->[1], $UNIV | $CONS | $SEQUENCE);
my $key = asn1_extract($tbs->[1], $UNIV | $CONS | $SEQUENCE);
my $issuer_uid = asn1_extract($tbs->[1], $CONT | $CONS | 1, 1);
my $subject_uid = asn1_extract($tbs->[1], $CONT | $CONS | 2, 1);
my $extension_list = asn1_extract($tbs->[1], $CONT | $CONS | 3, 1);
my $subject_key_id = ();
my $authority_key_id = ();
#
# Parse the extension list
#
if ($extension_list->[0] != -1) {
my $extensions = asn1_extract($extension_list->[1], $UNIV | $CONS | $SEQUENCE);
while ($extensions->[1]->[1] > 0) {
my $ext = asn1_extract($extensions->[1], $UNIV | $CONS | $SEQUENCE);
my $x_oid = asn1_extract($ext->[1], $UNIV | $OBJ_ID);
my $x_crit = asn1_extract($ext->[1], $UNIV | $BOOLEAN, 1);
my $x_val = asn1_extract($ext->[1], $UNIV | $OCTET_STRING);
my $raw_oid = asn1_retrieve($x_oid->[1]);
next if (!exists($OIDs{$raw_oid}));
my $x_type = $OIDs{$raw_oid};
my $raw_value = asn1_retrieve($x_val->[1]);
if ($x_type eq "subjectKeyIdentifier") {
my $vcursor = [ 0, length($raw_value), \$raw_value ];
$subject_key_id = asn1_extract($vcursor, $UNIV | $OCTET_STRING);
}
}
}
###############################################################################
#
# Determine what we're going to use as the signer's name. In order of
# preference, take one of: commonName, organizationName or emailAddress.
#
###############################################################################
my $org = "";
my $cn = "";
my $email = "";
while ($subject->[1]->[1] > 0) {
my $rdn = asn1_extract($subject->[1], $UNIV | $CONS | $SET);
my $attr = asn1_extract($rdn->[1], $UNIV | $CONS | $SEQUENCE);
my $n_oid = asn1_extract($attr->[1], $UNIV | $OBJ_ID);
my $n_val = asn1_extract($attr->[1], -1);
my $raw_oid = asn1_retrieve($n_oid->[1]);
next if (!exists($OIDs{$raw_oid}));
my $n_type = $OIDs{$raw_oid};
my $raw_value = asn1_retrieve($n_val->[1]);
if ($n_type eq "organizationName") {
$org = $raw_value;
} elsif ($n_type eq "commonName") {
$cn = $raw_value;
} elsif ($n_type eq "emailAddress") {
$email = $raw_value;
}
}
my $id_name = $email;
if ($org && $cn) {
# Don't use the organizationName if the commonName repeats it
if (length($org) <= length($cn) &&
substr($cn, 0, length($org)) eq $org) {
$id_name = $cn;
goto got_id_name;
}
# Or a signifcant chunk of it
if (length($org) >= 7 &&
length($cn) >= 7 &&
substr($cn, 0, 7) eq substr($org, 0, 7)) {
$id_name = $cn;
goto got_id_name;
}
$id_name = $org . ": " . $cn;
} elsif ($org) {
$id_name = $org;
} elsif ($cn) {
$id_name = $cn;
}
got_id_name:
###############################################################################
#
# Output the signer's name and the key identifier that we're going to include
# in module signatures.
#
###############################################################################
die $src, ": ", "X.509: Couldn't find the Subject Key Identifier extension\n"
if (!$subject_key_id);
my $id_key_id = asn1_retrieve($subject_key_id->[1]);
open(OUTFD, ">$ARGV[1]") || die $ARGV[1];
print OUTFD $id_name;
close OUTFD || die $ARGV[1];
open(OUTFD, ">$ARGV[2]") || die $ARGV[2];
print OUTFD $id_key_id;
close OUTFD || die $ARGV[2];
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