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) = @_;
18 my $digest = Digest::HMAC_SHA1::hmac_sha1($time . "/" . $id, $secret);
19 my @digest_bytes = _to_byte_array($digest);
21 # Mask the token to avoid the BREACH attack.
22 my $random = Bytes::Random::Secure::random_bytes(scalar @digest_bytes);
23 my @random_bytes = _to_byte_array($random);
25 my $masked_token = "";
27 for my $i (0..$#digest_bytes) {
28 $masked_token .= sprintf "%02x", ($digest_bytes[$i] ^ $random_bytes[$i]);
29 $mask .= sprintf "%02x", $random_bytes[$i];
32 return sprintf("%s,%s,%d", $masked_token, $mask, $time);
35 sub check_csrf_token {
36 my ($id, $secret, $csrf_token, $max_age) = @_;
38 if ($csrf_token !~ /^([0-9a-f]+),([0-9a-f]+),([0-9]+)$/) {
43 my ($masked_token, $mask, $time) = ($1, $2, $3);
44 if (defined($max_age) && time - $time > $max_age) {
49 my @masked_bytes = _to_byte_array(pack('H*', $masked_token));
50 my @mask_bytes = _to_byte_array(pack('H*', $mask));
52 my $correct_token = Digest::HMAC_SHA1::hmac_sha1($time . '/' . $id, $secret);
53 my @correct_bytes = _to_byte_array($correct_token);
55 if ($#masked_bytes != $#mask_bytes || $#masked_bytes != $#correct_bytes) {
56 # Malformed token (wrong number of characters).
60 # Compare in a way that should make timing attacks hard.
62 for my $i (0..$#masked_bytes) {
63 $mismatches += $masked_bytes[$i] ^ $mask_bytes[$i] ^ $correct_bytes[$i];
65 return ($mismatches == 0);
68 # Converts each byte in the given string to its numeric value,
69 # e.g., "ABCabc" becomes (65, 66, 67, 97, 98, 99).
71 return unpack("C*", $_[0]);