int HMAC_SHA256_final()

in src/hmac.c [82:111]

• 21 lines of code
• 8 McCabe index (conditional complexity)

int HMAC_SHA256_final(hmac_sha256 *ctx, char* out, int outlen)
{
    if (ctx == NULL || out == NULL)
        return ERR_NULLPOINTER_HMAC;
    if (outlen <= 0 || outlen > SHA256_HASH_SIZE)
        return ERR_BADARGLEN_HMAC;

    int i;
    char opad = 0x5c;
    char digest[SHA256_HASH_SIZE];

    // Compute H((k0 ^ ipad) || in)
    HASH256_hash(&(ctx->sha256_ctx), digest);

    // Compute `H((K0 ^ opad ) || H((K0 ^ ipad) || in))`
    for(i = 0; i < SHA256_BLOCK_SIZE; i++)
        HASH256_process(&(ctx->sha256_ctx), (ctx->k0)[i] ^ opad);
    for(i = 0; i < SHA256_HASH_SIZE; i++)
        HASH256_process(&(ctx->sha256_ctx), digest[i]);
    HASH256_hash(&(ctx->sha256_ctx), digest);

    // Erase the secret key as it is not needed anymore
    for(i = 0; i < SHA256_BLOCK_SIZE; i++)
        ctx->k0[i] = 0x00;

    for(i = 0; i < outlen; i++)
        out[i] = digest[i];

    return SUCCESS;
}