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206 lines
5.5 KiB
Perl
206 lines
5.5 KiB
Perl
#!/usr/bin/env perl
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##
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## Author......: See docs/credits.txt
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## License.....: MIT
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##
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use strict;
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use warnings;
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use Digest::SHA qw (hmac_sha1);
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use Crypt::Mode::CBC;
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use Crypt::PBKDF2;
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use Encode;
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use POSIX qw (strftime);
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sub byte2hex
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{
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my $input = shift;
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return unpack ("H*", $input);
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}
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sub hex2byte
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{
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my $input = shift;
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return pack ("H*", $input);
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}
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sub pad
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{
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my $n = shift;
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my $size = shift;
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return (~$n + 1) & ($size - 1);
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}
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sub module_constraints { [[0, 256], [16, 16], [-1, -1], [-1, -1], [-1, -1]] }
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sub module_generate_hash
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{
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my $word = shift;
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my $salt = shift;
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my $user = shift // "user";
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my $realm = shift // "realm";
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my $checksum = shift;
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my $enc_timestamp = shift;
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my $mysalt = uc $realm;
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$mysalt = $mysalt . $user;
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# first we generate the 'seed'
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my $iter = 4096;
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my $pbkdf2 = Crypt::PBKDF2->new
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(
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hash_class => 'HMACSHA1',
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iterations => $iter,
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output_len => 16
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);
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my $b_seed = $pbkdf2->PBKDF2 ($mysalt, $word);
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# we can precompute this
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my $b_kerberos_nfolded = hex2byte('6b65726265726f737b9b5b2b93132b93');
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my $b_iv = hex2byte('0' x 32);
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# 'key_bytes' will be the AES key used to generate 'ki' (for final hmac-sha1)
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# and 'ke' (AES key to decrypt/encrypt the ticket)
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my $cbc = Crypt::Mode::CBC->new ('AES', 0);
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my $b_key_bytes = $cbc->encrypt ($b_kerberos_nfolded, $b_seed, $b_iv);
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# precomputed stuff
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# nfold 0x0000000155 to 16 bytes
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my $b_nfolded1 = hex2byte('5b582c160a5aa80556ab55aad5402ab5');
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# nfold 0x00000001aa to 16 bytes
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my $b_nfolded2 = hex2byte('ae2c160b04ad5006ab55aad56a80355a');
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my $b_ki = $cbc->encrypt ($b_nfolded1, $b_key_bytes, $b_iv);
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my $b_ke = $cbc->encrypt ($b_nfolded2, $b_key_bytes, $b_iv);
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my $cleartext_ticket = '';
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my $check_correct = 0;
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if (defined $enc_timestamp)
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{
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# Do CTS Decryption https://en.wikipedia.org/wiki/Ciphertext_stealing
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# Decrypt n-1 block
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my $len_last_block = length($enc_timestamp) % 32;
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my $len_last_2_blocks = $len_last_block + 32;
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my $b_n_1_block = hex2byte (substr($enc_timestamp, -$len_last_2_blocks, 32));
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my $b_n_1_decrypted = $cbc->decrypt ($b_n_1_block, $b_ke, $b_iv);
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# Pad the last block with last bytes from the decrypted n-1
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my $b_padded_enc_ticket = hex2byte($enc_timestamp).(substr $b_n_1_decrypted, -(16 - $len_last_block/2));
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# Swap the last two blocks
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my $b_cbc_enc_ticket = (substr $b_padded_enc_ticket, 0, -32).(substr $b_padded_enc_ticket, -16, 16).
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(substr $b_padded_enc_ticket, -32, 16);
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# Decrypt and truncate
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my $b_dec_ticket_padded = $cbc->decrypt ($b_cbc_enc_ticket, $b_ke, $b_iv);
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my $b_cleartext_ticket = substr $b_dec_ticket_padded, 0, length($enc_timestamp)/2;
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$cleartext_ticket = byte2hex($b_cleartext_ticket);
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my $check_correct = ((substr ($b_cleartext_ticket, 22, 2) eq "20") &&
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(substr ($b_cleartext_ticket, 36, 1) eq "Z"));
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if ($check_correct == 1 && defined $checksum)
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{
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my $b_checksum = hmac_sha1 (hex2byte($cleartext_ticket), $b_ki);
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$check_correct = ($checksum eq byte2hex(substr $b_checksum, 0, 12));
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}
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}
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if ($check_correct != 1)
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{
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# fake/wrong ticket (otherwise if we just decrypt/encrypt we end
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#up with false positives all the time)
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$cleartext_ticket = '68c8459f3f10c851b8827118bb459c6e301aa011180f323031'.
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'32313131363134323835355aa10502030c28a2';
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# we have what is required to compute checksum
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$checksum = hmac_sha1 (hex2byte($cleartext_ticket), $b_ki);
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$checksum = byte2hex(substr $checksum, 0, 12);
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}
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# CTS Encrypt our new block
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my $len_cleartext_last_block = length($cleartext_ticket)%32;
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my $cleartext_last_block = substr $cleartext_ticket, -$len_cleartext_last_block;
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my $padding = pad(length($cleartext_ticket), 32);
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my $b_cleartext_last_block_padded = hex2byte($cleartext_last_block . '0' x $padding);
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# we will encrypt until n-1 block (included)
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my $truncated_cleartext_ticket = substr $cleartext_ticket, 0, -$len_cleartext_last_block;
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my $b_truncated_enc_ticket = $cbc->encrypt (hex2byte($truncated_cleartext_ticket), $b_ke, $b_iv);
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my $b_enc_ticket_n_1_block= substr $b_truncated_enc_ticket, -16;
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my $b_enc_last_block = substr $b_enc_ticket_n_1_block, 0, $len_cleartext_last_block/2;
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# we now craft the new n-1 block
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my $tmp = $b_enc_ticket_n_1_block ^ $b_cleartext_last_block_padded;
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$b_enc_ticket_n_1_block = $cbc->encrypt ($tmp, $b_ke, $b_iv);
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$tmp = substr $b_truncated_enc_ticket, 0, -16;
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$enc_timestamp = $tmp . $b_enc_ticket_n_1_block . $b_enc_last_block;
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my $tmp_hash = sprintf ('$krb5pa$17$%s$%s$%s%s', $user, $realm, unpack ("H*", $enc_timestamp), $checksum);
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return $tmp_hash;
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}
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sub module_verify_hash
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{
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my $line = shift;
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my ($hash, $word) = split (':', $line);
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return unless defined $hash;
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return unless defined $word;
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my @data = split ('\$', $hash);
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return unless scalar @data == 6;
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shift @data;
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my $signature = shift @data;
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my $algorithm = shift @data;
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my $user = shift @data;
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my $realm = shift @data;
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my $edata = shift @data;
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return unless ($signature eq "krb5pa");
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return unless ($algorithm eq "17");
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return unless (length ($edata) >= 88);
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return unless (length ($edata) <= 112);
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my $checksum = substr $edata, -24;
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my $enc_timestamp = substr $edata, 0, -24;
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my $word_packed = pack_if_HEX_notation ($word);
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my $new_hash = module_generate_hash ($word_packed, undef, $user, $realm, $checksum, $enc_timestamp);
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return ($new_hash, $word);
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}
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1;
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