Secure Hash Algorithm (SHA-1) Reference implementation in C/C++ with comments

The SHA-1 source code in C/C++ is given below. Comments are given in separate color.

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/*
******************************************************************
This source code is under development. Even though you can use it as
such, it is recommended you check back after a few hours for an updated
version. The current version lacks descriptive comments also.
******************************************************************
*/

#include<stdio.h>
#include<string.h>
#include<malloc.h>
#include<math.h>
#include<stdlib.h>

#define rotateleft(x,n) ((x<<n) | (x>>(32-n)))
#define rotateright(x,n) ((x>>n) | (x<<(32-n)))

void SHA1(unsigned char * str1)
{
unsigned long int h0,h1,h2,h3,h4,a,b,c,d,e,f,k,temp;

h0 = 0x67452301;
h1 = 0xEFCDAB89;
h2 = 0x98BADCFE;
h3 = 0x10325476;
h4 = 0xC3D2E1F0;

unsigned char * str;
str = (unsigned char *)malloc(strlen((const char *)str1)+100);
strcpy((char *)str,(const char *)str1);

int current_length = strlen((const char *)str);
int original_length = current_length;
str[current_length] = 0x80;
str[current_length + 1] = '\0';

char ic = str[current_length];
current_length++;

int ib = current_length % 64;
if(ib<56)
ib = 56-ib;
else
ib = 120 - ib;

for(int i=0;i < ib;i++)
{
str[current_length]=0x00;
current_length++;
}
str[current_length + 1]='\0';

for(i=0;i<6;i++)
{
str[current_length]=0x0;
current_length++;
}
str[current_length] = (original_length * 8) / 0x100 ;
current_length++;
str[current_length] = (original_length * 8) % 0x100;
current_length++;
str[current_length+i]='\0';
int number_of_chunks = current_length/64;
unsigned long int word[80];
for(i=0;i<number_of_chunks;i++)
{
for(int j=0;j<16;j++)
{
word[j] = str[i*64 + j*4 + 0] * 0x1000000 + str[i*64 + j*4 + 1] * 0x10000 + str[i*64 + j*4 + 2] * 0x100 + str[i*64 + j*4 + 3];
}
for(j=16;j<80;j++)
{
word[j] = rotateleft((word[j-3] ^ word[j-8] ^ word[j-14] ^ word[j-16]),1);
}

a = h0;
b = h1;
c = h2;
d = h3;
e = h4;

for(int m=0;m<80;m++)
{
if(m<=19)
{
f = (b & c) | ((~b) & d);
k = 0x5A827999;
}
else if(m<=39)
{
f = b ^ c ^ d;
k = 0x6ED9EBA1;
}

else if(m<=59)
{
f = (b & c) | (b & d) | (c & d);
k = 0x8F1BBCDC;
}

else
{
f = b ^ c ^ d;
k = 0xCA62C1D6;
}

temp = (rotateleft(a,5) + f + e + k + word[m]) & 0xFFFFFFFF;
e = d;
d = c;
c = rotateleft(b,30);
b = a;
a = temp;

}

h0 = h0 + a;
h1 = h1 + b;
h2 = h2 + c;
h3 = h3 + d;
h4 = h4 + e;

}

printf("\n\n");
printf("Hash: %x %x %x %x %x",h0, h1, h2, h3, h4);
printf("\n\n");
}

void main()
{
SHA1((unsigned char *)"The quick brown fox jumps over the lazy dog");
}

 

 

— End of Source code —

 

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Author: Niyaz PK

 

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