3

In the process of trying to learn Monero's codebase and attempting to modify it, I have come across this difficulty: after having a user to enter his/her passphrase (a string), I would like to compute it's hash.

Since I know that Monero uses SHA-3 (Keccak algorithm) in its cryptography, I was hoping that there would already exist a function implemented to do just that. So that is my question: is there a simple way to compute SHA-3(passphrase), or better, as I was originally intended, SHA-256(passphrase)? I am ideally looking for functions already defined in the codebase, but if that doesn't exist then I would appreciate any suggestions on how to go about implementing that.


Note: Using Olivier Gay's solution, as suggested below by 5chdn, seems to conflict with something inside of monero/src/crypto/slow-hash.c, which further suggests to me that the codebase already has a way of dealing with SHA-256.

2

For SHA-3, you have cn_fast_hash, with this prototype:

void cn_fast_hash(const void *data, std::size_t length, crypto::hash &hash);

crypto::hash is a 256 bit value.

1

First of all a disclaimer, I have no idea about the simplewallet.cpp and the monero client source code, but since this is a general coding question, let me get you started.

First of all you need a library (or write your own class) which knows how to compute a sha256 hash. I would recommend the free Crypto++ library. Here's a sample for HMAC.

Or, you can just create your own sha256.h, link it and add it your your code:

/* add this to simplewallet.cpp */
#include "sha256.h"

And create sha256.h file like that by Olivier Gay:

#ifndef SHA256_H
#define SHA256_H
#include <string>

class SHA256
{
protected:
    typedef unsigned char uint8;
    typedef unsigned int uint32;
    typedef unsigned long long uint64;

    const static uint32 sha256_k[];
    static const unsigned int SHA224_256_BLOCK_SIZE = (512/8);
public:
    void init();
    void update(const unsigned char *message, unsigned int len);
    void final(unsigned char *digest);
    static const unsigned int DIGEST_SIZE = ( 256 / 8);

protected:
    void transform(const unsigned char *message, unsigned int block_nb);
    unsigned int m_tot_len;
    unsigned int m_len;
    unsigned char m_block[2*SHA224_256_BLOCK_SIZE];
    uint32 m_h[8];
};

std::string sha256(std::string input);

#define SHA2_SHFR(x, n)    (x >> n)
#define SHA2_ROTR(x, n)   ((x >> n) | (x << ((sizeof(x) << 3) - n)))
#define SHA2_ROTL(x, n)   ((x << n) | (x >> ((sizeof(x) << 3) - n)))
#define SHA2_CH(x, y, z)  ((x & y) ^ (~x & z))
#define SHA2_MAJ(x, y, z) ((x & y) ^ (x & z) ^ (y & z))
#define SHA256_F1(x) (SHA2_ROTR(x,  2) ^ SHA2_ROTR(x, 13) ^ SHA2_ROTR(x, 22))
#define SHA256_F2(x) (SHA2_ROTR(x,  6) ^ SHA2_ROTR(x, 11) ^ SHA2_ROTR(x, 25))
#define SHA256_F3(x) (SHA2_ROTR(x,  7) ^ SHA2_ROTR(x, 18) ^ SHA2_SHFR(x,  3))
#define SHA256_F4(x) (SHA2_ROTR(x, 17) ^ SHA2_ROTR(x, 19) ^ SHA2_SHFR(x, 10))
#define SHA2_UNPACK32(x, str)                 \
{                                             \
    *((str) + 3) = (uint8) ((x)      );       \
    *((str) + 2) = (uint8) ((x) >>  8);       \
    *((str) + 1) = (uint8) ((x) >> 16);       \
    *((str) + 0) = (uint8) ((x) >> 24);       \
}
#define SHA2_PACK32(str, x)                   \
{                                             \
    *(x) =   ((uint32) *((str) + 3)      )    \
           | ((uint32) *((str) + 2) <<  8)    \
           | ((uint32) *((str) + 1) << 16)    \
           | ((uint32) *((str) + 0) << 24);   \
}
#endif

And sha256.cpp:

#include <cstring>
#include <fstream>
#include "sha256.h"

const unsigned int SHA256::sha256_k[64] = //UL = uint32
            {0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5,
             0x3956c25b, 0x59f111f1, 0x923f82a4, 0xab1c5ed5,
             0xd807aa98, 0x12835b01, 0x243185be, 0x550c7dc3,
             0x72be5d74, 0x80deb1fe, 0x9bdc06a7, 0xc19bf174,
             0xe49b69c1, 0xefbe4786, 0x0fc19dc6, 0x240ca1cc,
             0x2de92c6f, 0x4a7484aa, 0x5cb0a9dc, 0x76f988da,
             0x983e5152, 0xa831c66d, 0xb00327c8, 0xbf597fc7,
             0xc6e00bf3, 0xd5a79147, 0x06ca6351, 0x14292967,
             0x27b70a85, 0x2e1b2138, 0x4d2c6dfc, 0x53380d13,
             0x650a7354, 0x766a0abb, 0x81c2c92e, 0x92722c85,
             0xa2bfe8a1, 0xa81a664b, 0xc24b8b70, 0xc76c51a3,
             0xd192e819, 0xd6990624, 0xf40e3585, 0x106aa070,
             0x19a4c116, 0x1e376c08, 0x2748774c, 0x34b0bcb5,
             0x391c0cb3, 0x4ed8aa4a, 0x5b9cca4f, 0x682e6ff3,
             0x748f82ee, 0x78a5636f, 0x84c87814, 0x8cc70208,
             0x90befffa, 0xa4506ceb, 0xbef9a3f7, 0xc67178f2};

void SHA256::transform(const unsigned char *message, unsigned int block_nb)
{
    uint32 w[64];
    uint32 wv[8];
    uint32 t1, t2;
    const unsigned char *sub_block;
    int i;
    int j;
    for (i = 0; i < (int) block_nb; i++) {
        sub_block = message + (i << 6);
        for (j = 0; j < 16; j++) {
            SHA2_PACK32(&sub_block[j << 2], &w[j]);
        }
        for (j = 16; j < 64; j++) {
            w[j] =  SHA256_F4(w[j -  2]) + w[j -  7] + SHA256_F3(w[j - 15]) + w[j - 16];
        }
        for (j = 0; j < 8; j++) {
            wv[j] = m_h[j];
        }
        for (j = 0; j < 64; j++) {
            t1 = wv[7] + SHA256_F2(wv[4]) + SHA2_CH(wv[4], wv[5], wv[6])
                + sha256_k[j] + w[j];
            t2 = SHA256_F1(wv[0]) + SHA2_MAJ(wv[0], wv[1], wv[2]);
            wv[7] = wv[6];
            wv[6] = wv[5];
            wv[5] = wv[4];
            wv[4] = wv[3] + t1;
            wv[3] = wv[2];
            wv[2] = wv[1];
            wv[1] = wv[0];
            wv[0] = t1 + t2;
        }
        for (j = 0; j < 8; j++) {
            m_h[j] += wv[j];
        }
    }
}

void SHA256::init()
{
    m_h[0] = 0x6a09e667;
    m_h[1] = 0xbb67ae85;
    m_h[2] = 0x3c6ef372;
    m_h[3] = 0xa54ff53a;
    m_h[4] = 0x510e527f;
    m_h[5] = 0x9b05688c;
    m_h[6] = 0x1f83d9ab;
    m_h[7] = 0x5be0cd19;
    m_len = 0;
    m_tot_len = 0;
}

void SHA256::update(const unsigned char *message, unsigned int len)
{
    unsigned int block_nb;
    unsigned int new_len, rem_len, tmp_len;
    const unsigned char *shifted_message;
    tmp_len = SHA224_256_BLOCK_SIZE - m_len;
    rem_len = len < tmp_len ? len : tmp_len;
    memcpy(&m_block[m_len], message, rem_len);
    if (m_len + len < SHA224_256_BLOCK_SIZE) {
        m_len += len;
        return;
    }
    new_len = len - rem_len;
    block_nb = new_len / SHA224_256_BLOCK_SIZE;
    shifted_message = message + rem_len;
    transform(m_block, 1);
    transform(shifted_message, block_nb);
    rem_len = new_len % SHA224_256_BLOCK_SIZE;
    memcpy(m_block, &shifted_message[block_nb << 6], rem_len);
    m_len = rem_len;
    m_tot_len += (block_nb + 1) << 6;
}

void SHA256::final(unsigned char *digest)
{
    unsigned int block_nb;
    unsigned int pm_len;
    unsigned int len_b;
    int i;
    block_nb = (1 + ((SHA224_256_BLOCK_SIZE - 9)
                     < (m_len % SHA224_256_BLOCK_SIZE)));
    len_b = (m_tot_len + m_len) << 3;
    pm_len = block_nb << 6;
    memset(m_block + m_len, 0, pm_len - m_len);
    m_block[m_len] = 0x80;
    SHA2_UNPACK32(len_b, m_block + pm_len - 4);
    transform(m_block, block_nb);
    for (i = 0 ; i < 8; i++) {
        SHA2_UNPACK32(m_h[i], &digest[i << 2]);
    }
}

std::string sha256(std::string input)
{
    unsigned char digest[SHA256::DIGEST_SIZE];
    memset(digest,0,SHA256::DIGEST_SIZE);

    SHA256 ctx = SHA256();
    ctx.init();
    ctx.update( (unsigned char*)input.c_str(), input.length());
    ctx.final(digest);

    char buf[2*SHA256::DIGEST_SIZE+1];
    buf[2*SHA256::DIGEST_SIZE] = 0;
    for (int i = 0; i < SHA256::DIGEST_SIZE; i++)
        sprintf(buf+i*2, "%02x", digest[i]);
    return std::string(buf);
}

If you link the file correctly, you should be able to do a sha256(string) as initially asked.

  • This did help me get past the make without an error, thank you.// On the other hand, when I do try to use the function, there seems to be a conflict with some predefined notion of SHA-256 in the crypto codebase, so maybe there is more to it in Monero's codebase already. – user141 Oct 28 '16 at 12:27

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