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expand bcrypt discussion
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‎docs/bcrypt.md‎

Lines changed: 191 additions & 1 deletion
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@@ -52,6 +52,7 @@ $cdata = array_values(unpack('N*', 'OrpheanBeholderScryDoubt'));
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for ($j = 0; $j < 6; $j += 2) { // count($cdata) == 6
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#
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#-----[ FIND ]------------------------------------------
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# in 3.0.39+ this'll be V* - not L*
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#
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return pack('L*', ...$cdata);
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#
@@ -108,4 +109,193 @@ function encodeBase64($input)
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return $output;
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}
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```
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The two key takeaways from this are: (1) `Blowfish::bcrypt_hash()` expects 64 byte inputs whereas the normal bcrypt uses 8 byte salts and variable length passwords and (2) the last byte of `Blowfish::bcrypt_hash()` need to be removed.
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The two key takeaways from this are: (1) `Blowfish::bcrypt_hash()` expects 64 byte inputs whereas the normal bcrypt uses 16 byte salts and variable length passwords and (2) the last byte of `Blowfish::bcrypt_hash()` need to be removed.
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If one wanted to make `Blowfish::bcrypt_hash()` support variable length passwords and 16 byte salts the following additional changes would need to be made:
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```
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#
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#-----[ FIND ]------------------------------------------
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# in bcrypt_hash()
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#
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$sha2pass = array_values(unpack('N*', $sha2pass));
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#
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#-----[ BEFORE, ADD ]-----------------------------------
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#
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// per the $2a$ bit we append a null byte and then "treat the password as cyclic"
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$sha2pass.= "\0";
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while (strlen($sha2pass) < 72) {
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$sha2pass.= $sha2pass;
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}
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$sha2pass = substr($sha2pass, 0, 72);
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#
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#-----[ FIND ]------------------------------------------
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# in expand0state()
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#
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$p = [
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$p[0] ^ $key[0],
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$p[1] ^ $key[1],
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$p[2] ^ $key[2],
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$p[3] ^ $key[3],
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$p[4] ^ $key[4],
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$p[5] ^ $key[5],
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$p[6] ^ $key[6],
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$p[7] ^ $key[7],
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$p[8] ^ $key[8],
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$p[9] ^ $key[9],
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$p[10] ^ $key[10],
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$p[11] ^ $key[11],
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$p[12] ^ $key[12],
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$p[13] ^ $key[13],
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$p[14] ^ $key[14],
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$p[15] ^ $key[15],
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$p[16] ^ $key[0],
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$p[17] ^ $key[1]
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];
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#
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#-----[ REPLACE WITH ]----------------------------------
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# this is a documented change; we can't keep the loop unrolled version
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# unless we expand the salt out to 72 bytes as well to match the password
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# size
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#
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for ($i = 0; $i < 18; $i++) {
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$p[$i]^= $key[$i % count($key)];
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}
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#
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#-----[ FIND ]------------------------------------------
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# in expandstate()
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#
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$p[16] ^ $key[0],
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$p[17] ^ $key[1]
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#
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#-----[ REPLACE WITH ]----------------------------------
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# this is a documented change
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#
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$p[16] ^ $key[16],
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$p[17] ^ $key[17]
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#
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#-----[ FIND ]------------------------------------------
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# in expandstate()
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#
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// @codingStandardsIgnoreStart
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list( $p[0], $p[1]) = self::encryptBlockHelperFast($data[ 0] , $data[ 1] , $sbox, $p);
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list( $p[2], $p[3]) = self::encryptBlockHelperFast($data[ 2] ^ $p[ 0], $data[ 3] ^ $p[ 1], $sbox, $p);
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list( $p[4], $p[5]) = self::encryptBlockHelperFast($data[ 4] ^ $p[ 2], $data[ 5] ^ $p[ 3], $sbox, $p);
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list( $p[6], $p[7]) = self::encryptBlockHelperFast($data[ 6] ^ $p[ 4], $data[ 7] ^ $p[ 5], $sbox, $p);
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list( $p[8], $p[9]) = self::encryptBlockHelperFast($data[ 8] ^ $p[ 6], $data[ 9] ^ $p[ 7], $sbox, $p);
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list($p[10], $p[11]) = self::encryptBlockHelperFast($data[10] ^ $p[ 8], $data[11] ^ $p[ 9], $sbox, $p);
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list($p[12], $p[13]) = self::encryptBlockHelperFast($data[12] ^ $p[10], $data[13] ^ $p[11], $sbox, $p);
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list($p[14], $p[15]) = self::encryptBlockHelperFast($data[14] ^ $p[12], $data[15] ^ $p[13], $sbox, $p);
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list($p[16], $p[17]) = self::encryptBlockHelperFast($data[ 0] ^ $p[14], $data[ 1] ^ $p[15], $sbox, $p);
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// @codingStandardsIgnoreEnd
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list($sbox[0], $sbox[1]) = self::encryptBlockHelperFast($data[2] ^ $p[16], $data[3] ^ $p[17], $sbox, $p);
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for ($i = 2, $j = 4; $i < 1024; $i += 2, $j = ($j + 2) % 16) { // instead of 16 maybe count($data) would be better?
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list($sbox[$i], $sbox[$i + 1]) = self::encryptBlockHelperFast($data[$j] ^ $sbox[$i - 2], $data[$j + 1] ^ $sbox[$i - 1], $sbox, $p);
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}
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#
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#-----[ REPLACE WITH ]----------------------------------
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# this is a documented change; instead of doing $data[0]..$data[15] we're doing $data[0]..$data[3] cyclically
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#
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// @codingStandardsIgnoreStart
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list( $p[0], $p[1]) = self::encryptBlockHelperFast($data[ 0] , $data[ 1] , $sbox, $p);
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list( $p[2], $p[3]) = self::encryptBlockHelperFast($data[ 2] ^ $p[ 0], $data[ 3] ^ $p[ 1], $sbox, $p);
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list( $p[4], $p[5]) = self::encryptBlockHelperFast($data[ 0] ^ $p[ 2], $data[ 1] ^ $p[ 3], $sbox, $p);
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list( $p[6], $p[7]) = self::encryptBlockHelperFast($data[ 2] ^ $p[ 4], $data[ 3] ^ $p[ 5], $sbox, $p);
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list( $p[8], $p[9]) = self::encryptBlockHelperFast($data[ 0] ^ $p[ 6], $data[ 1] ^ $p[ 7], $sbox, $p);
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list($p[10], $p[11]) = self::encryptBlockHelperFast($data[ 2] ^ $p[ 8], $data[ 3] ^ $p[ 9], $sbox, $p);
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list($p[12], $p[13]) = self::encryptBlockHelperFast($data[ 0] ^ $p[10], $data[ 1] ^ $p[11], $sbox, $p);
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list($p[14], $p[15]) = self::encryptBlockHelperFast($data[ 2] ^ $p[12], $data[ 3] ^ $p[13], $sbox, $p);
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list($p[16], $p[17]) = self::encryptBlockHelperFast($data[ 0] ^ $p[14], $data[ 1] ^ $p[15], $sbox, $p);
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// @codingStandardsIgnoreEnd
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list($sbox[0], $sbox[1]) = self::encryptBlockHelperFast($data[2] ^ $p[16], $data[3] ^ $p[17], $sbox, $p);
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for ($i = 2, $j = 0; $i < 1024; $i += 2, $j%= 4) { // instead of 16 maybe count($data) would be better?
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list($sbox[$i], $sbox[$i + 1]) = self::encryptBlockHelperFast($data[$j++] ^ $sbox[$i - 2], $data[$j++] ^ $sbox[$i - 1], $sbox, $p);
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}
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```
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## Making Wikipedia match OpenSSH
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The following changes (notated using the [phpBB MOD Text Template](phpbb.md#actions)) are for [revision 08:07, 14 May 2024 of wikipedia's bcrypt article](https://en.wikipedia.org/w/index.php?title=Bcrypt&oldid=1223800920#Algorithm). They may or may not work on other revision.
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```
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#
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#-----[ FIND ]------------------------------------------
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# in Function bcrypt
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#
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Input:
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password: array of Bytes (1..72 bytes) UTF-8 encoded password
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salt: array of Bytes (16 bytes) random salt
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cost: Number (4..31) log2(Iterations). e.g. 12 ==> 2**12 = 4,096 iterations
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#
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#-----[ REPLACE WITH ]----------------------------------
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# this is a documented change; well, the cost isn't, but everything else is
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#
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Input:
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password: array of Bytes (64 bytes) UTF-8 encoded password
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salt: array of Bytes (64 bytes) random salt
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cost: Number (6) 64 iterations
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#
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#-----[ FIND ]------------------------------------------
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# in Function bcrypt
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#
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ctext ← "OrpheanBeholderScryDoubt" //24 bytes ==> three 64-bit blocks
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#
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#-----[ REPLACE WITH ]----------------------------------
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# this is a documented change
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#
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ctext ← "OxychromaticBlowfishSwatDynamite" //32 bytes ==> four 64-bit blocks
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#
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#-----[ FIND ]------------------------------------------
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# in Function EksBlowfishSetup
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#
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P, S ← ExpandKey(P, S, password, 0)
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P, S ← ExpandKey(P, S, salt, 0)
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#
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#-----[ REPLACE WITH ]----------------------------------
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# this is an undocumented change; we're just swapping the order
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#
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P, S ← ExpandKey(P, S, salt, 0)
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P, S ← ExpandKey(P, S, password, 0)
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#
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#-----[ FIND ]------------------------------------------
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# in Function ExpandKey
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#
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//Treat the 128-bit salt as two 64-bit halves (the Blowfish block size).
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saltHalf[0] ← salt[0..63] //Lower 64-bits of salt
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saltHalf[1] ← salt[64..127] //Upper 64-bits of salt
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#
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#-----[ REPLACE WITH ]----------------------------------
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# this is a documented change
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#
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saltChunk[0] ← salt[0..63]
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saltChunk[1] ← salt[64..127]
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saltChunk[2] ← salt[128..191]
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saltChunk[3] ← salt[192..255]
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saltChunk[4] ← salt[256..319]
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saltChunk[5] ← salt[320..383]
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saltChunk[6] ← salt[384..447]
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saltChunk[7] ← salt[448..511]
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#
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#-----[ FIND ]------------------------------------------
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# in Function ExpandKey
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#
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block ← block xor saltHalf[(n-1) mod 2] //each iteration alternating between saltHalf[0], and saltHalf[1]
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#
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#-----[ REPLACE WITH ]----------------------------------
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# this is a documented change
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#
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block ← block xor saltChunk[n-1]
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#
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#-----[ FIND ]------------------------------------------
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# in Function ExpandKey
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#
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block ← Encrypt(state, block xor saltHalf[(n-1) mod 2]) //as above
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#
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#-----[ REPLACE WITH ]----------------------------------
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# this is a documented change
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#
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block ← Encrypt(state, block xor saltChunk[(n-1) mod 8])
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```
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Being pseudo code this doesn't quite capture everything. For example it doesn't capture the change in endianness.

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