bool hashlib_PBKDF2(const uint8_t* password, size_t plen, uint8_t* out, const uint8_t* salt, size_t salt_len, size_t iter_count, size_t keylen){

    uint8_t sha_buffer[SHA256_OUTSIZE];
    uint8_t sha_comp[SHA256_OUTSIZE];
    size_t outlen;
    SHA256_CTX ctx;
    uint32_t mbuffer[64];
    uint32_t counter = 1;

    if(password==NULL || out==NULL) return false;
    if(plen==0) return false;
    if(iter_count<1) return false;
    if(keylen==0) return false;
    //HASH = sha256
    // DK = T(i) for i in 0 => (keylen/HASH), concat

    for(outlen = 0; outlen < keylen; outlen+=SHA256_OUTSIZE, counter++){
        //T(i) = F(password, salt, c, i) = U1 xor U2 xor ... xor Uc
            //U1 = PRF1(Password, Salt + INT_32_BE(i))
            //U2 = PRF(Password, U1)
            //⋮
            //Uc = PRF(Password, Uc)
        size_t copylen = ((keylen-outlen) > SHA256_OUTSIZE) ? SHA256_OUTSIZE : keylen-outlen;
        uint8_t c[4];
        c[0] = (counter >> 24) & 0xff;
		c[1] = (counter >> 16) & 0xff;
		c[2] = (counter >> 8) & 0xff;
		c[3] = (counter >> 0) & 0xff;
        hashlib_Sha256Init(&ctx, mbuffer);
        hashlib_Sha256Update(&ctx, password, plen);
        hashlib_Sha256Update(&ctx, salt, salt_len);
        hashlib_Sha256Update(&ctx, c, sizeof c);
        hashlib_Sha256Final(&ctx, sha_comp);
        for(size_t ic=1; ic<iter_count; ic++){
            hashlib_Sha256Init(&ctx, NULL);
            hashlib_Sha256Update(&ctx, password, plen);
            hashlib_Sha256Update(&ctx, sha_comp, SHA256_OUTSIZE);
            hashlib_Sha256Final(&ctx, sha_buffer);
            for(uint8_t j=0; j<SHA256_OUTSIZE; j++)
                sha_comp[j] ^= sha_buffer[j];
        }
        memcpy(&out[outlen], sha_comp, copylen);
    }
    return true;
}