4 use Bytes::Random::Secure;
9 our @ISA = qw(Exporter);
10 our @EXPORT_OK = qw(generate_csrf_token check_csrf_token);
11 our $VERSION = '1.00';
13 sub generate_csrf_token {
14 my ($id, $secret, $options) = @_;
16 my $time = $options->{'Time'} // time;
17 my $random = $options->{'Random'};
19 my $digest = Digest::HMAC_SHA1::hmac_sha1($time . "/" . $id, $secret);
20 my @digest_bytes = _to_byte_array($digest);
22 # Mask the token to avoid the BREACH attack.
23 if (!defined($random) || length($random) != length($digest)) {
24 $random = Bytes::Random::Secure::random_bytes(scalar @digest_bytes);
26 my @random_bytes = _to_byte_array($random);
28 my $masked_token = "";
30 for my $i (0..$#digest_bytes) {
31 $masked_token .= sprintf "%02x", ($digest_bytes[$i] ^ $random_bytes[$i]);
32 $mask .= sprintf "%02x", $random_bytes[$i];
35 return sprintf("%s,%s,%d", $masked_token, $mask, $time);
38 sub check_csrf_token {
39 my ($id, $secret, $csrf_token, $options) = @_;
41 if ($csrf_token !~ /^([0-9a-f]+),([0-9a-f]+),([0-9]+)$/) {
46 my $ref_time = $options->{'Time'} // time;
48 my ($masked_token, $mask, $time) = ($1, $2, $3);
49 my $max_age = $options->{'MaxAge'};
50 if (defined($max_age) && $ref_time - $time > $max_age) {
55 my @masked_bytes = _to_byte_array(pack('H*', $masked_token));
56 my @mask_bytes = _to_byte_array(pack('H*', $mask));
58 my $correct_token = Digest::HMAC_SHA1::hmac_sha1($time . '/' . $id, $secret);
59 my @correct_bytes = _to_byte_array($correct_token);
61 if ($#masked_bytes != $#mask_bytes || $#masked_bytes != $#correct_bytes) {
62 # Malformed token (wrong number of characters).
66 # Compare in a way that should make timing attacks hard.
68 for my $i (0..$#masked_bytes) {
69 $mismatches += $masked_bytes[$i] ^ $mask_bytes[$i] ^ $correct_bytes[$i];
71 return ($mismatches == 0);
74 # Converts each byte in the given string to its numeric value,
75 # e.g., "ABCabc" becomes (65, 66, 67, 97, 98, 99).
77 return unpack("C*", $_[0]);