OpenSSL MD5 Hashing Example in C++

This tutorial will guide you on how to hash a string by using OpenSSL’s MD5 hash function. This tutorial will create two C++ example files which will compile and run in Ubuntu environment.

1. Make sure that we have both OpenSSL & libssl-dev installed in the system.
   ~$ dpkg --get-selections | grep openssl
   openssl     install
   ~$ dpkg --get-selections | grep libssl
   libssl-dev    install
   libssl-doc    install
   libssl1.0.0   install
2. Install the modules in case there are not available in your system:
   ~$ sudo apt-get install openssl
   ~$ sudo apt-get install libssl-dev
3. Here are the openssl md5 sample source code.
   
   Example #1: md5_sample1.cpp
   C++

   #include <stdio.h> #include <string.h> #include <openssl/md5.h> int main() { unsigned char digest[MD5_DIGEST_LENGTH]; char string[] = "happy"; MD5((unsigned char*)&string, strlen(string), (unsigned char*)&digest); char mdString[33]; for(int i = 0; i < 16; i++) sprintf(&mdString[i*2], "%02x", (unsigned int)digest[i]); printf("md5 digest: %s\n", mdString); return 0; }

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   #include <stdio.h> #include <string.h> #include <openssl/md5.h>   int main() {     unsigned char digest[MD5_DIGEST_LENGTH];     char string[] = "happy";          MD5((unsigned char*)&string, strlen(string), (unsigned char*)&digest);           char mdString[33];       for(int i = 0; i < 16; i++)          sprintf(&mdString[i*2], "%02x", (unsigned int)digest[i]);       printf("md5 digest: %s\n", mdString);       return 0; }

   
   Example #2: md5_sample2.cpp

   C++

   #include <stdio.h> #include <string.h> #include <openssl/md5.h> int main() { unsigned char digest[16]; const char* string = "happy"; printf("string length: %d\n", strlen(string)); MD5_CTX ctx; MD5_Init(&ctx); MD5_Update(&ctx, string, strlen(string)); MD5_Final(digest, &ctx); char mdString[33]; for (int i = 0; i < 16; i++) sprintf(&mdString[i*2], "%02x", (unsigned int)digest[i]); printf("md5 digest: %s\n", mdString); return 0; }

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   #include <stdio.h> #include <string.h> #include <openssl/md5.h>   int main() {     unsigned char digest[16];     const char* string = "happy";       printf("string length: %d\n", strlen(string));       MD5_CTX ctx;     MD5_Init(&ctx);     MD5_Update(&ctx, string, strlen(string));     MD5_Final(digest, &ctx);       char mdString[33];     for (int i = 0; i < 16; i++)         sprintf(&mdString[i*2], "%02x", (unsigned int)digest[i]);       printf("md5 digest: %s\n", mdString);       return 0; }

4. Let’s try to compile both sample cpp files and you should observe the following output screenshot.
   ~$ gcc md5_sample1.cpp -o sample1 -lcrypto
   ~$ ./sample1
   md5 digest: 5eb53bbbe01eeed093cb22bb8f5acdc3
   ~$ gcc md5_sample2.cpp -o sample2 -lcrypto
   ~$ ./sample2
   md5 digest: 5eb53bbbe01eeed093cb22bb8f5acdc3
   Note: -lcrypto will include the crypto library from openssl