C++ sha1 function


The SHA-1 is a widely used hashing algorithm. It was thought to provide 80 bits of security, but recent attacks have shown weaknesses and have reduced it to 69 bits. Though not considered "broken" like MD5, SHA-1 is considered deprecated since 2010 for digital signatures and other secure applications, and SHA-2 should be considered instead. For instance, SSL certificates will soon all have SHA-2 hashes, and be signed by SHA-2 intermediates.

If used for password hashing, any hash algorithm should include a unique random salt for each password hash for protection, as it reduces the value of a dictionary attack against your password list. It is also good to include a work factor. For instance, a work factor of 8, means you should apply 2^8 (256) rounds of SHA-1 to the password and salt, then store the work factor next to the salt along with the hashed password.

The following code outputs the sha1 hash as a hex string, and I checked it against the php sha1 function.

main.cpp
#include <iostream>
#include "sha1.h"
 
using namespace std;
 
int main(int argc, char *argv[])
{
    cout << "sha1('grape'):" << sha1("grape") << endl;
    return 0;
}

compile and run (linux):
g++ main.cpp sha1.cpp -o sha1_sample && ./sha1_sample
output:
sha1('grape'):bc8a2f8cdedb005b5c787692853709b060db75ff

sha1.h
/*
    sha1.h - header of
 
    ============
    SHA-1 in C++
    ============
 
    100% Public Domain.
 
    Original C Code
        -- Steve Reid <steve@edmweb.com>
    Small changes to fit into bglibs
        -- Bruce Guenter <bruce@untroubled.org>
    Translation to simpler C++ Code
        -- Volker Grabsch <vog@notjusthosting.com>
*/
 
#ifndef SHA1_HPP
#define SHA1_HPP
 
 
#include <iostream>
#include <string>
 
class SHA1
{
public:
    SHA1();
    void update(const std::string &s);
    void update(std::istream &is);
    std::string final();
    static std::string from_file(const std::string &filename);
 
private:
    typedef unsigned long int uint32;   /* just needs to be at least 32bit */
    typedef unsigned long long uint64;  /* just needs to be at least 64bit */
 
    static const unsigned int DIGEST_INTS = 5;  /* number of 32bit integers per SHA1 digest */
    static const unsigned int BLOCK_INTS = 16;  /* number of 32bit integers per SHA1 block */
    static const unsigned int BLOCK_BYTES = BLOCK_INTS * 4;
 
    uint32 digest[DIGEST_INTS];
    std::string buffer;
    uint64 transforms;
 
    void reset();
    void transform(uint32 block[BLOCK_BYTES]);
 
    static void buffer_to_block(const std::string &buffer, uint32 block[BLOCK_BYTES]);
    static void read(std::istream &is, std::string &s, int max);
};
 
std::string sha1(const std::string &string);
 
 
 
#endif /* SHA1_HPP */

sha1.cpp
/*
    sha1.cpp - source code of
 
    ============
    SHA-1 in C++
    ============
 
    100% Public Domain.
 
    Original C Code
        -- Steve Reid <steve@edmweb.com>
    Small changes to fit into bglibs
        -- Bruce Guenter <bruce@untroubled.org>
    Translation to simpler C++ Code
        -- Volker Grabsch <vog@notjusthosting.com>
*/
 
#include "sha1.h"
#include <sstream>
#include <iomanip>
#include <fstream>
 
/* Help macros */
#define SHA1_ROL(value, bits) (((value) << (bits)) | (((value) & 0xffffffff) >> (32 - (bits))))
#define SHA1_BLK(i) (block[i&15] = SHA1_ROL(block[(i+13)&15] ^ block[(i+8)&15] ^ block[(i+2)&15] ^ block[i&15],1))
 
/* (R0+R1), R2, R3, R4 are the different operations used in SHA1 */
#define SHA1_R0(v,w,x,y,z,i) z += ((w&(x^y))^y)     + block[i]    + 0x5a827999 + SHA1_ROL(v,5); w=SHA1_ROL(w,30);
#define SHA1_R1(v,w,x,y,z,i) z += ((w&(x^y))^y)     + SHA1_BLK(i) + 0x5a827999 + SHA1_ROL(v,5); w=SHA1_ROL(w,30);
#define SHA1_R2(v,w,x,y,z,i) z += (w^x^y)           + SHA1_BLK(i) + 0x6ed9eba1 + SHA1_ROL(v,5); w=SHA1_ROL(w,30);
#define SHA1_R3(v,w,x,y,z,i) z += (((w|x)&y)|(w&x)) + SHA1_BLK(i) + 0x8f1bbcdc + SHA1_ROL(v,5); w=SHA1_ROL(w,30);
#define SHA1_R4(v,w,x,y,z,i) z += (w^x^y)           + SHA1_BLK(i) + 0xca62c1d6 + SHA1_ROL(v,5); w=SHA1_ROL(w,30);
 
SHA1::SHA1()
{
    reset();
}
 
 
void SHA1::update(const std::string &s)
{
    std::istringstream is(s);
    update(is);
}
 
 
void SHA1::update(std::istream &is)
{
    std::string rest_of_buffer;
    read(is, rest_of_buffer, BLOCK_BYTES - buffer.size());
    buffer += rest_of_buffer;
 
    while (is)
    {
        uint32 block[BLOCK_INTS];
        buffer_to_block(buffer, block);
        transform(block);
        read(is, buffer, BLOCK_BYTES);
    }
}
 
 
/*
 * Add padding and return the message digest.
 */
 
std::string SHA1::final()
{
    /* Total number of hashed bits */
    uint64 total_bits = (transforms*BLOCK_BYTES + buffer.size()) * 8;
 
    /* Padding */
    buffer += 0x80;
    unsigned int orig_size = buffer.size();
    while (buffer.size() < BLOCK_BYTES)
    {
        buffer += (char)0x00;
    }
 
    uint32 block[BLOCK_INTS];
    buffer_to_block(buffer, block);
 
    if (orig_size > BLOCK_BYTES - 8)
    {
        transform(block);
        for (unsigned int i = 0; i < BLOCK_INTS - 2; i++)
        {
            block[i] = 0;
        }
    }
 
    /* Append total_bits, split this uint64 into two uint32 */
    block[BLOCK_INTS - 1] = total_bits;
    block[BLOCK_INTS - 2] = (total_bits >> 32);
    transform(block);
 
    /* Hex std::string */
    std::ostringstream result;
    for (unsigned int i = 0; i < DIGEST_INTS; i++)
    {
        result << std::hex << std::setfill('0') << std::setw(8);
        result << (digest[i] & 0xffffffff);
    }
 
    /* Reset for next run */
    reset();
 
    return result.str();
}
 
 
std::string SHA1::from_file(const std::string &filename)
{
    std::ifstream stream(filename.c_str(), std::ios::binary);
    SHA1 checksum;
    checksum.update(stream);
    return checksum.final();
}
 
 
void SHA1::reset()
{
    /* SHA1 initialization constants */
    digest[0] = 0x67452301;
    digest[1] = 0xefcdab89;
    digest[2] = 0x98badcfe;
    digest[3] = 0x10325476;
    digest[4] = 0xc3d2e1f0;
 
    /* Reset counters */
    transforms = 0;
    buffer = "";
}
 
 
/*
 * Hash a single 512-bit block. This is the core of the algorithm.
 */
 
void SHA1::transform(uint32 block[BLOCK_BYTES])
{
    /* Copy digest[] to working vars */
    uint32 a = digest[0];
    uint32 b = digest[1];
    uint32 c = digest[2];
    uint32 d = digest[3];
    uint32 e = digest[4];
 
 
    /* 4 rounds of 20 operations each. Loop unrolled. */
    SHA1_R0(a,b,c,d,e, 0);
    SHA1_R0(e,a,b,c,d, 1);
    SHA1_R0(d,e,a,b,c, 2);
    SHA1_R0(c,d,e,a,b, 3);
    SHA1_R0(b,c,d,e,a, 4);
    SHA1_R0(a,b,c,d,e, 5);
    SHA1_R0(e,a,b,c,d, 6);
    SHA1_R0(d,e,a,b,c, 7);
    SHA1_R0(c,d,e,a,b, 8);
    SHA1_R0(b,c,d,e,a, 9);
    SHA1_R0(a,b,c,d,e,10);
    SHA1_R0(e,a,b,c,d,11);
    SHA1_R0(d,e,a,b,c,12);
    SHA1_R0(c,d,e,a,b,13);
    SHA1_R0(b,c,d,e,a,14);
    SHA1_R0(a,b,c,d,e,15);
    SHA1_R1(e,a,b,c,d,16);
    SHA1_R1(d,e,a,b,c,17);
    SHA1_R1(c,d,e,a,b,18);
    SHA1_R1(b,c,d,e,a,19);
    SHA1_R2(a,b,c,d,e,20);
    SHA1_R2(e,a,b,c,d,21);
    SHA1_R2(d,e,a,b,c,22);
    SHA1_R2(c,d,e,a,b,23);
    SHA1_R2(b,c,d,e,a,24);
    SHA1_R2(a,b,c,d,e,25);
    SHA1_R2(e,a,b,c,d,26);
    SHA1_R2(d,e,a,b,c,27);
    SHA1_R2(c,d,e,a,b,28);
    SHA1_R2(b,c,d,e,a,29);
    SHA1_R2(a,b,c,d,e,30);
    SHA1_R2(e,a,b,c,d,31);
    SHA1_R2(d,e,a,b,c,32);
    SHA1_R2(c,d,e,a,b,33);
    SHA1_R2(b,c,d,e,a,34);
    SHA1_R2(a,b,c,d,e,35);
    SHA1_R2(e,a,b,c,d,36);
    SHA1_R2(d,e,a,b,c,37);
    SHA1_R2(c,d,e,a,b,38);
    SHA1_R2(b,c,d,e,a,39);
    SHA1_R3(a,b,c,d,e,40);
    SHA1_R3(e,a,b,c,d,41);
    SHA1_R3(d,e,a,b,c,42);
    SHA1_R3(c,d,e,a,b,43);
    SHA1_R3(b,c,d,e,a,44);
    SHA1_R3(a,b,c,d,e,45);
    SHA1_R3(e,a,b,c,d,46);
    SHA1_R3(d,e,a,b,c,47);
    SHA1_R3(c,d,e,a,b,48);
    SHA1_R3(b,c,d,e,a,49);
    SHA1_R3(a,b,c,d,e,50);
    SHA1_R3(e,a,b,c,d,51);
    SHA1_R3(d,e,a,b,c,52);
    SHA1_R3(c,d,e,a,b,53);
    SHA1_R3(b,c,d,e,a,54);
    SHA1_R3(a,b,c,d,e,55);
    SHA1_R3(e,a,b,c,d,56);
    SHA1_R3(d,e,a,b,c,57);
    SHA1_R3(c,d,e,a,b,58);
    SHA1_R3(b,c,d,e,a,59);
    SHA1_R4(a,b,c,d,e,60);
    SHA1_R4(e,a,b,c,d,61);
    SHA1_R4(d,e,a,b,c,62);
    SHA1_R4(c,d,e,a,b,63);
    SHA1_R4(b,c,d,e,a,64);
    SHA1_R4(a,b,c,d,e,65);
    SHA1_R4(e,a,b,c,d,66);
    SHA1_R4(d,e,a,b,c,67);
    SHA1_R4(c,d,e,a,b,68);
    SHA1_R4(b,c,d,e,a,69);
    SHA1_R4(a,b,c,d,e,70);
    SHA1_R4(e,a,b,c,d,71);
    SHA1_R4(d,e,a,b,c,72);
    SHA1_R4(c,d,e,a,b,73);
    SHA1_R4(b,c,d,e,a,74);
    SHA1_R4(a,b,c,d,e,75);
    SHA1_R4(e,a,b,c,d,76);
    SHA1_R4(d,e,a,b,c,77);
    SHA1_R4(c,d,e,a,b,78);
    SHA1_R4(b,c,d,e,a,79);
 
    /* Add the working vars back into digest[] */
    digest[0] += a;
    digest[1] += b;
    digest[2] += c;
    digest[3] += d;
    digest[4] += e;
 
    /* Count the number of transformations */
    transforms++;
}
 
 
void SHA1::buffer_to_block(const std::string &buffer, uint32 block[BLOCK_BYTES])
{
    /* Convert the std::string (byte buffer) to a uint32 array (MSB) */
    for (unsigned int i = 0; i < BLOCK_INTS; i++)
    {
        block[i] = (buffer[4*i+3] & 0xff)
                   | (buffer[4*i+2] & 0xff)<<8
                   | (buffer[4*i+1] & 0xff)<<16
                   | (buffer[4*i+0] & 0xff)<<24;
    }
}
 
 
void SHA1::read(std::istream &is, std::string &s, int max)
{
    char sbuf[max];
    is.read(sbuf, max);
    s.assign(sbuf, is.gcount());
}
 
 
std::string sha1(const std::string &string)
{
    SHA1 checksum;
    checksum.update(string);
    return checksum.final();
}
code snippets are licensed under Creative Commons CC-By-SA 3.0 (unless otherwise specified)