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#264485 - 05/12/18 01:50 AM .$hmac $totp $hotp 65-128 keylength sha384/sha512
maroon Offline
Hoopy frood

Registered: 12/01/04
Posts: 966
$hmac returns an invalid string when using hash sha384 or sha512 when key length is 65-128 bytes (not characters). The likely cause is treating these hashes as having the same 512-bit chunk/block (not digest length) size as sha224, sha256, sha1, and md5. sha384 and sha512 actually have a 1024-bit (128 bytes) chunk/block size.

Because they use HMAC as one of the steps in calculating their output, this also has a related effect on $hotp and $totp when their key parameter has the same length and they're using either of these 2 hashes.

All other HMAC length/hash combos i've tested are good, and this does not affect the $sha384 and $sha512 identifiers when used separate from HMAC.

1. https://www.freeformatter.com/hmac-generator.html
2. change digest dropdown to sha512
3. Paste 65-byte clipboard into the 'string' and 'secret key' boxes
4. Compare computed HMAC against the identifier
5. Repeat #3-4 after changing dropdown to sha384

Code:
//clipboard $str(z,65) | echo -a sha384 $hmac($cb,$cb,sha384)
current: sha384 32066b46d8b36d0ba060a32c6798256c9e20c812b08bbc3814e1d512353cc01172cfc426d972ca233cf7793aa4d15e9f
website: sha384 02695828d419569796c74efb9e854f345106da0889c19faf31cdab86221cbbc492b480ebf30d8e4cb7f1d734f2980ed1

//clipboard $str(z,65) | echo -a sha512 $hmac($cb,$cb,sha512)
current: sha512 dbddf5022df3b5dcabc94d6dd540f27a069706c6dcd9441de73c781f8941380a2025f7514fa3fd329a354b69d885d2e3d9305ca138b8d3a86737d193f20e162b
website: sha512 c90181b3a36d1bf889954a73a29a1cc86a6ee08e8f4f80e57b066cfcc81a79bcf3c050809c88380802355fad74786c25f42330a9ebb8e275230c519c280e4efa



The issue affecting $hotp and $totp is different than the issue affecting all hashtypes i reported in the thread below, where text passphrases can be interpreted as base32, base32+spaces can be interpreted as hex, etc.

https://forums.mirc.com/ubbthreads.php/topics/263454/Re:_$hotp()_base-32_decoding#Post263454

All the test vectors I find for HOTP and TOTP used shorter keys, but I believe that fixing this HMAC chunk size should result in these changed outputs without altering the $hotp or $totp code at all:

Code:
//echo 3 -a $hotp($str(!,65),123,sha512,9)
current: 254082140
changed: 153475474

//echo 4 -a $totp($str(!,65),123,sha512,9,30)
current: 126760220
changed: 457836172

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#264488 - 05/12/18 01:27 PM Re: .$hmac $totp $hotp 65-128 keylength sha384/sha512 [Re: maroon]
Khaled Offline


Planetary brain

Registered: 04/12/02
Posts: 4295
Loc: London, UK
Thanks for your bug report and the test scripts showing the expected output. The issue was due to the initial shortening of the key if it was longer than the block size. The key was being shortened if it was larger than 64 bytes for all hashes, when it should only be shortened for sha384/512 if it is longer than 128 bytes. This has been fixed for the next version.

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