Commit 85ecac79 authored by David Howells's avatar David Howells Committed by Rusty Russell
Browse files

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: default avatarDavid Howells <dhowells@redhat.com>
Signed-off-by: default avatarRusty Russell <rusty@rustcorp.com.au>
parent 48ba2462

scripts/x509keyid

0 → 100755
+268 −0
Original line number Diff line number Diff line 
#!/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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