Dakshina`s Blog

Sunday Dec 10, 2006

Aaj ki seekh: MD5 api

The MD5 algo takes as input a messge of arbitrary length and
produces a 128-bit message digest or fingerprint of the input.

For more info on MD5 refer to the RFC page

http://www.ietf.org/rfc/rfc1321.txt

Just a simple program to show usage of MD5 API to calculate a message digest.

#include <stdio.h>
#include <md5.h>

/* Link with the -lmd5 library */
/* gcc -lmd5 <program_name> */

/* this program generates a 128 bit MD5 digest of a given string */

main(){

int i=0;
unsigned char *buffer="We shall generate a message digest of this string";
unsigned char *output=(unsigned char *)malloc(16*sizeof(char)) ; /* store the 128 bit digest in this string */

printf("\n-Using the md5_calc functions ----\n");
md5_calc(output, buffer,strlen(buffer));
for(i=0;i<16;i++)
printf("%d:",(int)(output[i]));

printf("\n-Using the MD5 functions ----\n");
MD5_CTX context;
MD5Init(&context);
MD5Update(&context,buffer,strlen(buffer));
MD5Final(output,&context);
for(i=0;i<16;i++){
printf("%d:",(int)(output[i]));
}
free(output);
}

The output: (the digest is displayed as colon seperated )

--Using the md5_calc functions ----
208:123:118:146:90:32:215:98:10:11:23:26:78:229:127:76:
-Using the MD5 functions ----
208:123:118:146:90:32:215:98:10:11:23:26:78:229:127:76:

Posted at 04:37PM Dec 10, 2006 by dakshina in Sun | Comments[0]

Tuesday Dec 05, 2006

what i learnt today :encrypt

Today :

I came across a utilty ,encrypt for encrypting files.

encrypt: usage: encrypt -l | -a <algorithm> [-k <keyfile>] [-i <infile>]
[-o <outfile>]
This comes with the Solaris package SUNWcsu .

These are the algorithms it supports :

#encrypt -l
Algorithm       Keysize: Min   Max (bits)
------------------------------------------
aes                       128   128
arcfour                   8    128
des                        64     64
3des                     192 192

Posted at 06:11PM Dec 05, 2006 by dakshina in Sun | Comments[0]

Friday Dec 01, 2006

Getting the output of a shell command from a C program using popen

Sometimes its necessary to access the output of a shell command(more than just the return value) in a C program. One way could be to redirect it to a file and then access it .The other would be by using the popen function.

#include<stdio.h>

main(){
char cmd[80];
FILE *fptr;
char out[256];
int ret;
strcpy(cmd,"ls -l");
fptr = popen(cmd, "r");
while(1){
        fgets(out, 256, fptr);
        if(feof(fptr)) break;
        puts(out);
}
ret = pclose(fptr);
}

/* Noted tested with S10 gcc only ..*/

Posted at 10:52AM Dec 01, 2006 by dakshina in Sun | Comments[0]