Question

I want to write a program to hash some data and preferably i would like it to use sha1 or MD5 any of those. I don’t know the main logic behind it. I also wanted to know what ways i can take to do it in C.

Answer 1

Use a libray like this (SHA1, SHA256, SHA384, SHA512, MD5, Base64) or, just for MD5, this code

MD5

MD5.H

/* $Id: md5.h,v 1.3 2006-01-02 18:16:26 quentin Exp $ */

/*
  * Implementation of the md5 algorithm described in RFC1321
  * Copyright (C) 2005 Quentin Carbonneaux <[e-mail]>
  * 
 * This file is part of md5sum.
  *
  * md5sum is a free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
  * the Free Softawre Foundation; either version 2 of the License, or
  * (at your option) any later version.
  *
  * md5sum is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  * GNU General Public License for more details.
  *
  * You should hav received a copy of the GNU General Public License
  * along with md5sum; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
  */

#ifndef MD5_H
 #define MD5_H

#include <assert.h>
 #include <stdlib.h>

/* WARNING :
  * This implementation is using 32 bits long values for sizes
  */
 typedef unsigned int md5_size;

/* MD5 context */
 struct md5_ctx {
         struct {
                 unsigned int A, B, C, D; /* registers */
         } regs;
         unsigned char *buf;
         md5_size size;
         md5_size bits;
 };

/* Size of the MD5 buffer */
 #define MD5_BUFFER 1024

/* Basic md5 functions */
 #define F(x,y,z) ((x & y) | (~x & z))
 #define G(x,y,z) ((x & z) | (~z & y))
 #define H(x,y,z) (x ^ y ^ z)
 #define I(x,y,z) (y ^ (x | ~z))

/* Rotate left 32 bits values (words) */
 #define ROTATE_LEFT(w,s) ((w << s) | ((w & 0xFFFFFFFF) >> (32 - s)))

#define FF(a,b,c,d,x,s,t) (a = b + ROTATE_LEFT((a + F(b,c,d) + x + t), s))
 #define GG(a,b,c,d,x,s,t) (a = b + ROTATE_LEFT((a + G(b,c,d) + x + t), s))
 #define HH(a,b,c,d,x,s,t) (a = b + ROTATE_LEFT((a + H(b,c,d) + x + t), s))
 #define II(a,b,c,d,x,s,t) (a = b + ROTATE_LEFT((a + I(b,c,d) + x + t), s))

unsigned char *md5 (unsigned char *, md5_size, unsigned char *);
 void md5_init (struct md5_ctx *);
 void md5_update (struct md5_ctx *context);
 void md5_final (unsigned char *digest, struct md5_ctx *context);

#endif /* MD5_H */ 

MD5.c

/* $Id: md5.c,v 1.3 2006-05-01 16:57:31 quentin Exp $ */

/*
  * Implementation of the md5 algorithm as described in RFC1321
  * Copyright (C) 2005 Quentin Carbonneaux <[e-mail]>
  * 
 * This file is part of md5sum.
  *
  * md5sum is a free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
  * the Free Softawre Foundation; either version 2 of the License, or
  * (at your option) any later version.
  *
  * md5sum is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  * GNU General Public License for more details.
  *
  * You should hav received a copy of the GNU General Public License
  * along with md5sum; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
  */

#include "md5.h"

#define S11 7
 #define S12 12
 #define S13 17
 #define S14 22
 #define S21 5
 #define S22 9
 #define S23 14
 #define S24 20
 #define S31 4
 #define S32 11
 #define S33 16
 #define S34 23
 #define S41 6
 #define S42 10
 #define S43 15
 #define S44 21


#define memcopy(a,b,c) md5_memcopy ((a), (b), (c))
 #define memset(a,b,c) md5_memset ((a), (b), (c))

#define GET_UINT32(a,b,i)                            \
 {                                                 \
         (a) = ( (unsigned int) (b)[(i)  ]      )  \
             | ( (unsigned int) (b)[(i)+1] << 8 )        \
             | ( (unsigned int) (b)[(i)+2] << 16)        \
             | ( (unsigned int) (b)[(i)+3] << 24);       \
 }

/* local functions */
 static void md5_memcopy (unsigned char *, unsigned char *, const unsigned int);
 static void md5_memset (unsigned char *, const unsigned char, const unsigned int);
 static void md5_addsize (unsigned char *, md5_size , md5_size);
 static void md5_encode (unsigned char *, struct md5_ctx *);

static unsigned char MD5_PADDING [64] = { /* 512 Bits */
         0x80, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
            0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
            0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
            0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
 };

/*
  * An easy way to do the md5 sum of a short memory space
  */
 unsigned char *md5 (unsigned char *M, md5_size len, unsigned char *_digest)
 {
         int buflen = (len > MD5_BUFFER) ? MD5_BUFFER: len;
         struct md5_ctx *context;

        context = malloc (sizeof (struct md5_ctx));
         context->buf = malloc (buflen);
         context->size = 0;
         context->bits = 0;

        /* Init registries */
         context->regs.A = 0x67452301;
         context->regs.B = 0xefcdab89;
         context->regs.C = 0x98badcfe;
         context->regs.D = 0x10325476;

        do {
                 memcopy (context->buf + context->size, M + context->bits, buflen - context->size);
                 context->size += buflen - context->size;
                 md5_update (context);
         } while (len - context->bits > 64);

        md5_final (_digest, context);

        free (context->buf);
         free (context);

        return _digest;
 }

void md5_init (struct md5_ctx *context)
 {
         context->buf = malloc (MD5_BUFFER);
         memset (context->buf, '\0', MD5_BUFFER);
         context->size = 0;
         context->bits = 0;

        /* Init registries */
         context->regs.A = 0x67452301;
         context->regs.B = 0xefcdab89;
         context->regs.C = 0x98badcfe;
         context->regs.D = 0x10325476;
 }

/* md5_size is bytes while the size at the end of the message is in bits ... */
 static void md5_addsize (unsigned char *M, md5_size index, md5_size oldlen)
 {
         assert (((index * 8) % 512) == 448); /* If padding is not done then exit */

        M[index++] = (unsigned char) ((oldlen << 3) & 0xFF);
         M[index++] = (unsigned char) ((oldlen >> 5) & 0xFF);
         M[index++] = (unsigned char) ((oldlen >> 13) & 0xFF);
         M[index++] = (unsigned char) ((oldlen >> 21) & 0xFF);
         /* Fill with 0 because md5_size is 32 bits long */
         M[index++] = 0; M[index++] = 0;
         M[index++] = 0; M[index++] = 0;
 }

/*
  * Update a context by concatenating a new block
  */
 void md5_update (struct md5_ctx *context)
 {
         unsigned char buffer [64]; /* 512 bits */
         int i;

        for (i = 0; context->size - i > 63; i += 64) {
                 memcopy (buffer, context->buf + i, 64);
                 md5_encode (buffer, context);
                 context->bits += 64;
         }
         memcopy (buffer, context->buf + i, context->size - i);
         memcopy (context->buf, buffer, context->size - i);
         context->size -= i;
 }

void md5_final (unsigned char *digest, struct md5_ctx *context)
 {
         unsigned char buffer [64]; /* 512 bits */
         int i;

        assert (context->size < 64);

        if (context->size + 1 > 56) { /* We have to create another block */
                 memcopy (buffer, context->buf, context->size);
                 memcopy (buffer + context->size, MD5_PADDING, 64 - context->size);
                 md5_encode (buffer, context);
                 context->bits += context->size;
                 context->size = 0;
                 /* Proceed final block */
                 memset (buffer, '\0', 56);
                 /*memcopy (buffer, MD5_PADDING + 1, 56);*/
                 md5_addsize (buffer, 56, context->bits);
                 md5_encode (buffer, context);
         } else {
                 memcopy (buffer, context->buf, context->size);
                 context->bits += context->size;

                memcopy (buffer + context->size, MD5_PADDING, 56 - context->size);
                 md5_addsize (buffer, 56, context->bits);
                 md5_encode (buffer, context);
         }
         /* update digest */
         for (i = 0; i < 4; i++)
                 digest [i] = (unsigned char) ((context->regs.A >> (i*8)) & 0xFF);
         for (; i < 8; i++)
                 digest [i] = (unsigned char) ((context->regs.B >> ((i-4)*8)) & 0xFF);
         for (; i < 12; i++)
                 digest [i] = (unsigned char) ((context->regs.C >> ((i-8)*8)) & 0xFF);
         for (; i < 16; i++)
                 digest [i] = (unsigned char) ((context->regs.D >> ((i-12)*8)) & 0xFF);
 }

static void md5_encode (unsigned char *buffer, struct md5_ctx *context)
 {
         unsigned int a = context->regs.A, b = context->regs.B, c = context->regs.C, d = context->regs.D;
         unsigned int x[16];

        GET_UINT32 (x[ 0],buffer, 0);
         GET_UINT32 (x[ 1],buffer, 4);
         GET_UINT32 (x[ 2],buffer, 8);
         GET_UINT32 (x[ 3],buffer,12);
         GET_UINT32 (x[ 4],buffer,16);
         GET_UINT32 (x[ 5],buffer,20);
         GET_UINT32 (x[ 6],buffer,24);
         GET_UINT32 (x[ 7],buffer,28);
         GET_UINT32 (x[ 8],buffer,32);
         GET_UINT32 (x[ 9],buffer,36);
         GET_UINT32 (x[10],buffer,40);
         GET_UINT32 (x[11],buffer,44);
         GET_UINT32 (x[12],buffer,48);
         GET_UINT32 (x[13],buffer,52);
         GET_UINT32 (x[14],buffer,56);
         GET_UINT32 (x[15],buffer,60);

        /* Round 1 */
         FF (a, b, c, d, x[ 0], S11, 0xd76aa478); /* 1 */
         FF (d, a, b, c, x[ 1], S12, 0xe8c7b756); /* 2 */
         FF (c, d, a, b, x[ 2], S13, 0x242070db); /* 3 */
         FF (b, c, d, a, x[ 3], S14, 0xc1bdceee); /* 4 */
         FF (a, b, c, d, x[ 4], S11, 0xf57c0faf); /* 5 */
         FF (d, a, b, c, x[ 5], S12, 0x4787c62a); /* 6 */
         FF (c, d, a, b, x[ 6], S13, 0xa8304613); /* 7 */
         FF (b, c, d, a, x[ 7], S14, 0xfd469501); /* 8 */
         FF (a, b, c, d, x[ 8], S11, 0x698098d8); /* 9 */
         FF (d, a, b, c, x[ 9], S12, 0x8b44f7af); /* 10 */
         FF (c, d, a, b, x[10], S13, 0xffff5bb1); /* 11 */
         FF (b, c, d, a, x[11], S14, 0x895cd7be); /* 12 */
         FF (a, b, c, d, x[12], S11, 0x6b901122); /* 13 */
         FF (d, a, b, c, x[13], S12, 0xfd987193); /* 14 */
         FF (c, d, a, b, x[14], S13, 0xa679438e); /* 15 */
         FF (b, c, d, a, x[15], S14, 0x49b40821); /* 16 */

        /* Round 2 */
         GG (a, b, c, d, x[ 1], S21, 0xf61e2562); /* 17 */
         GG (d, a, b, c, x[ 6], S22, 0xc040b340); /* 18 */
         GG (c, d, a, b, x[11], S23, 0x265e5a51); /* 19 */
         GG (b, c, d, a, x[ 0], S24, 0xe9b6c7aa); /* 20 */
         GG (a, b, c, d, x[ 5], S21, 0xd62f105d); /* 21 */
         GG (d, a, b, c, x[10], S22,  0x2441453); /* 22 */
         GG (c, d, a, b, x[15], S23, 0xd8a1e681); /* 23 */
         GG (b, c, d, a, x[ 4], S24, 0xe7d3fbc8); /* 24 */
         GG (a, b, c, d, x[ 9], S21, 0x21e1cde6); /* 25 */
         GG (d, a, b, c, x[14], S22, 0xc33707d6); /* 26 */
         GG (c, d, a, b, x[ 3], S23, 0xf4d50d87); /* 27 */

        GG (b, c, d, a, x[ 8], S24, 0x455a14ed); /* 28 */
         GG (a, b, c, d, x[13], S21, 0xa9e3e905); /* 29 */
         GG (d, a, b, c, x[ 2], S22, 0xfcefa3f8); /* 30 */
         GG (c, d, a, b, x[ 7], S23, 0x676f02d9); /* 31 */
         GG (b, c, d, a, x[12], S24, 0x8d2a4c8a); /* 32 */

        /* Round 3 */
         HH (a, b, c, d, x[ 5], S31, 0xfffa3942); /* 33 */
         HH (d, a, b, c, x[ 8], S32, 0x8771f681); /* 34 */
         HH (c, d, a, b, x[11], S33, 0x6d9d6122); /* 35 */
         HH (b, c, d, a, x[14], S34, 0xfde5380c); /* 36 */
         HH (a, b, c, d, x[ 1], S31, 0xa4beea44); /* 37 */
         HH (d, a, b, c, x[ 4], S32, 0x4bdecfa9); /* 38 */
         HH (c, d, a, b, x[ 7], S33, 0xf6bb4b60); /* 39 */
         HH (b, c, d, a, x[10], S34, 0xbebfbc70); /* 40 */
         HH (a, b, c, d, x[13], S31, 0x289b7ec6); /* 41 */
         HH (d, a, b, c, x[ 0], S32, 0xeaa127fa); /* 42 */
         HH (c, d, a, b, x[ 3], S33, 0xd4ef3085); /* 43 */
         HH (b, c, d, a, x[ 6], S34,  0x4881d05); /* 44 */
         HH (a, b, c, d, x[ 9], S31, 0xd9d4d039); /* 45 */
         HH (d, a, b, c, x[12], S32, 0xe6db99e5); /* 46 */
         HH (c, d, a, b, x[15], S33, 0x1fa27cf8); /* 47 */
         HH (b, c, d, a, x[ 2], S34, 0xc4ac5665); /* 48 */

        /* Round 4 */
         II (a, b, c, d, x[ 0], S41, 0xf4292244); /* 49 */
         II (d, a, b, c, x[ 7], S42, 0x432aff97); /* 50 */
         II (c, d, a, b, x[14], S43, 0xab9423a7); /* 51 */
         II (b, c, d, a, x[ 5], S44, 0xfc93a039); /* 52 */
         II (a, b, c, d, x[12], S41, 0x655b59c3); /* 53 */
         II (d, a, b, c, x[ 3], S42, 0x8f0ccc92); /* 54 */
         II (c, d, a, b, x[10], S43, 0xffeff47d); /* 55 */
         II (b, c, d, a, x[ 1], S44, 0x85845dd1); /* 56 */
         II (a, b, c, d, x[ 8], S41, 0x6fa87e4f); /* 57 */
         II (d, a, b, c, x[15], S42, 0xfe2ce6e0); /* 58 */
         II (c, d, a, b, x[ 6], S43, 0xa3014314); /* 59 */
         II (b, c, d, a, x[13], S44, 0x4e0811a1); /* 60 */
         II (a, b, c, d, x[ 4], S41, 0xf7537e82); /* 61 */
         II (d, a, b, c, x[11], S42, 0xbd3af235); /* 62 */
         II (c, d, a, b, x[ 2], S43, 0x2ad7d2bb); /* 63 */
         II (b, c, d, a, x[ 9], S44, 0xeb86d391); /* 64 */

        context->regs.A += a;
         context->regs.B += b;
         context->regs.C += c;
         context->regs.D += d;
 }

/* OBSOLETE */
 static void md5_memcopy (unsigned char *dest, unsigned char *src, unsigned int count)
 {
         unsigned int i;

        for (i = 0; i < count; i++) {
                 dest [i] = src [i];
         }
 }

static void md5_memset (unsigned char *p, const unsigned char c, const unsigned int count)
 {
         unsigned int i;

        for (i = 0; i < count; i++) {
                 p [i] = c;
         }
 }

Example

const char *md5sum(const char *chaine, size_t len = 0)
 {
     struct md5_ctx ctx;
     unsigned char digest(16);
     md5_init(&ctx);
     ctx.size = len?len:strlen(chaine);
     strcpy(ctx.buf, chaine);
     md5_update(&ctx);
     md5_final(digest, &ctx);
     return digest;
 }