SHA512_HMAC

[ruro]

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 !