Function PBKDF2_SHA256

src/crypto/scrypt.cpp:123–173

* 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). */

 * 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));
}

static inline uint32_t
le32dec_2(const void * pp)