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+--- Thread: SHA512_HMAC (/thread-9690.html)
SHA512_HMAC - ruro - 12-05-2020
Good day !
I am attempting to write a module where I derive a key from 2048 SHA512_HMAC iterations, however I cannot seem to get the hash correct after the initial hash.
This is what I am trying
Code:
sha512_hmac_ctx_t ctx0;
sha512_hmac_init_swap(&ctx0, &pw, pwl);
sha512_hmac_update_swap(&ctx0, &salt, 12);
sha512_hmac_final(&ctx0);
print_u64_array_hex(&ctx0.opad.h, 8);
memcpy(&seed, &ctx0.opad.h, 64);
//xor_seed_with_round(&seed, &ctx0.opad.h);
u64 U[16] = {0};
memcpy(&U, &ctx0.opad.h, 64);
for(int x=1;x<2048;x++){
sha512_hmac_ctx_t ctx;
sha512_hmac_init_swap(&ctx, &pw, pwl);
sha512_hmac_update_swap(&ctx, U, 64);
sha512_hmac_final(&ctx);
if (x == 1) { print_u64_array_hex(&ctx.opad.h, 8); }
memcpy(&U, &ctx.opad.h, 64);
xor_seed_with_round(&seed, &U);
}As I mentioned, the initial hash at ctx0 is correct, however just after one iteration in the loop, the hash is wrong. I know the hash is wrong because I have a working implementation in Golang.
The same issue I have with normal sha512 as well, where I can get the first hash as expected, but then it just works unexpectedly.
Would appreciate any help
Thanks !
RE: SHA512_HMAC - ruro - 12-06-2020
Found the issue
seems like byte order is different for the output
my quick'n'dirty solution was to convert to uchar array after every iteration
Code:
for (int i=0; i<8; i++) {
U[i*8] = (ctx0.opad.h[i] & 0xFF00000000000000) >> 56;
U[i*8+1] = (ctx0.opad.h[i] & 0x00FF000000000000) >> 48;
U[i*8+2] = (ctx0.opad.h[i] & 0x0000FF0000000000) >> 40;
U[i*8+3] = (ctx0.opad.h[i] & 0x000000FF00000000) >> 32;
U[i*8+4] = (ctx0.opad.h[i] & 0x00000000FF000000) >> 24;
U[i*8+5] = (ctx0.opad.h[i] & 0x0000000000FF0000) >> 16;
U[i*8+6] = (ctx0.opad.h[i] & 0x000000000000FF00) >> 8;
U[i*8+7] = ctx0.opad.h[i] & 0x00000000000000FF;
}would still be interested to know if am mis-using the API, and if there are better fixes.