// Copyright (c) 2013 NovaCoin Developers

#include <string.h>
#include "pbkdf2.h"

static inline uint32_t
be32dec(const void *pp)
{
    const uint8_t *p = (uint8_t const *)pp;

    return ((uint32_t)(p[3]) + ((uint32_t)(p[2]) << 8) +
        ((uint32_t)(p[1]) << 16) + ((uint32_t)(p[0]) << 24));
}

static inline void
be32enc(void *pp, uint32_t x)
{
    uint8_t * p = (uint8_t *)pp;

    p[3] = x & 0xff;
    p[2] = (x >> 8) & 0xff;
    p[1] = (x >> 16) & 0xff;
    p[0] = (x >> 24) & 0xff;
}



/* Initialize an HMAC-SHA256 operation with the given key. */
void
HMAC_SHA256_Init(HMAC_SHA256_CTX * ctx, const void * _K, size_t Klen)
{
    unsigned char pad[64];
    unsigned char khash[32];
    const unsigned char * K = (const unsigned char *)_K;
    size_t i;

    /* If Klen > 64, the key is really SHA256(K). */
    if (Klen > 64) {
        SHA256_Init(&ctx->ictx);
        SHA256_Update(&ctx->ictx, K, Klen);
        SHA256_Final(khash, &ctx->ictx);
        K = khash;
        Klen = 32;
    }

    /* Inner SHA256 operation is SHA256(K xor [block of 0x36] || data). */
    SHA256_Init(&ctx->ictx);
    memset(pad, 0x36, 64);
    for (i = 0; i < Klen; i++)
        pad[i] ^= K[i];
    SHA256_Update(&ctx->ictx, pad, 64);

    /* Outer SHA256 operation is SHA256(K xor [block of 0x5c] || hash). */
    SHA256_Init(&ctx->octx);
    memset(pad, 0x5c, 64);
    for (i = 0; i < Klen; i++)
        pad[i] ^= K[i];
    SHA256_Update(&ctx->octx, pad, 64);

    /* Clean the stack. */
    memset(khash, 0, 32);
}

/* Add bytes to the HMAC-SHA256 operation. */
void
HMAC_SHA256_Update(HMAC_SHA256_CTX * ctx, const void *in, size_t len)
{

    /* Feed data to the inner SHA256 operation. */
    SHA256_Update(&ctx->ictx, in, len);
}

/* Finish an HMAC-SHA256 operation. */
void
HMAC_SHA256_Final(unsigned char digest[32], HMAC_SHA256_CTX * ctx)
{
    unsigned char ihash[32];

    /* Finish the inner SHA256 operation. */
    SHA256_Final(ihash, &ctx->ictx);

    /* Feed the inner hash to the outer SHA256 operation. */
    SHA256_Update(&ctx->octx, ihash, 32);

    /* Finish the outer SHA256 operation. */
    SHA256_Final(digest, &ctx->octx);

    /* Clean the stack. */
    memset(ihash, 0, 32);
}

/**
 * PBKDF2_SHA256(passwd, passwdlen, salt, saltlen, c, buf, dkLen):
 * Compute PBKDF2(passwd, salt, c, dkLen) using HMAC-SHA256 as the PRF, and
 * write the output to buf.  The value dkLen must be at most 32 * (2^32 - 1).
 */
void
PBKDF2_SHA256(const uint8_t * passwd, size_t passwdlen, const uint8_t * salt,
    size_t saltlen, uint64_t c, uint8_t * buf, size_t dkLen)
{
    HMAC_SHA256_CTX PShctx, hctx;
    size_t i;
    uint8_t ivec[4];
    uint8_t U[32];
    uint8_t T[32];
    uint64_t j;
    int k;
    size_t clen;

    /* Compute HMAC state after processing P and S. */
    HMAC_SHA256_Init(&PShctx, passwd, passwdlen);
    HMAC_SHA256_Update(&PShctx, salt, saltlen);

    /* Iterate through the blocks. */
    for (i = 0; i * 32 < dkLen; i++) {
        /* Generate INT(i + 1). */
        be32enc(ivec, (uint32_t)(i + 1));

        /* Compute U_1 = PRF(P, S || INT(i)). */
        memcpy(&hctx, &PShctx, sizeof(HMAC_SHA256_CTX));
        HMAC_SHA256_Update(&hctx, ivec, 4);
        HMAC_SHA256_Final(U, &hctx);

        /* T_i = U_1 ... */
        memcpy(T, U, 32);

        for (j = 2; j <= c; j++) {
            /* Compute U_j. */
            HMAC_SHA256_Init(&hctx, passwd, passwdlen);
            HMAC_SHA256_Update(&hctx, U, 32);
            HMAC_SHA256_Final(U, &hctx);

            /* ... xor U_j ... */
            for (k = 0; k < 32; k++)
                T[k] ^= U[k];
        }

        /* Copy as many bytes as necessary into buf. */
        clen = dkLen - i * 32;
        if (clen > 32)
            clen = 32;
        memcpy(&buf[i * 32], T, clen);
    }

    /* Clean PShctx, since we never called _Final on it. */
    memset(&PShctx, 0, sizeof(HMAC_SHA256_CTX));
}