Hi,
I'm implementing a new block cipher algorithm which is GOST 28147-89. This is a
256-bit key and 64-bit block algorithm. This algorithm works well with ECB, CBC
and CTR modes. But, when I try to use the XTS mode, the encryption fails. So I
tried to find the problem and it seems to come from the file crypto/xts.c,
function init_tfm :
if (crypto_cipher_blocksize(cipher) != XTS_BLOCK_SIZE) {
*flags |= CRYPTO_TFM_RES_BAD_BLOCK_LEN;
crypto_free_cipher(cipher);
return -EINVAL;
}
So, I checked the value of XTS_BLOCK_SIZE which is 0x10. The snag is that the
block size of GOST is 0x8. So I changed the block value of my algorithm to 0x10,
and then I tried again with the XTS mode, and it works!
Because of what just happened, I've two questions:
Q1: Why does the GOST algorithm still work? Despite I changed the block size.
Q2: Why in the code, was the block size of XTS fixed? As far as I know,
operations modes should adapt to the size of the block cipher.
Regards,
Thanks in advance
--
Jonathan "Coldshell" Thieuleux
Mail : [email protected]
IRC : coldshell [Freenode, OFTC]
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"If you write interfaces with more than 4 or 5 function arguments, it's possible that you and I cannot be friends." -- David Miller