OpenSSL SHA256 Hashing Example in C++

This tutorial will guide you on how to hash a string by using OpenSSL’s SHA256 hash function. This tutorial will create two C++ example files which will compile and run in Ubuntu environment.

1. Here are the openssl SHA256 sample source code.
   
   Example #1: sha256_sample1.cpp

   #include <stdio.h>
   #include <string.h>
   #include <openssl/sha.h>
   
   int main()
   {
       unsigned char digest[SHA256_DIGEST_LENGTH];
       char string[] = "hello world";
       
       SHA256((unsigned char*)&string, strlen(string), (unsigned char*)&digest);    
   
       char mdString[SHA256_DIGEST_LENGTH*2+1];
   
       for(int i = 0; i < SHA256_DIGEST_LENGTH; i++)
            sprintf(&mdString[i*2], "%02x", (unsigned int)digest[i]);
   
       printf("SHA256 digest: %s\n", mdString);
   
       return 0;
   }

   
   Example #2: sha256_sample2.cpp

   #include <stdio.h>
   #include <string.h>
   #include <openssl/sha.h>
   
   int main() {
       unsigned char digest[SHA256_DIGEST_LENGTH];
       const char* string = "hello world"; 
   
       SHA256_CTX ctx;
       SHA256_Init(&ctx);
       SHA256_Update(&ctx, string, strlen(string));
       SHA256_Final(digest, &ctx);
   
       char mdString[SHA256_DIGEST_LENGTH*2+1];
       for (int i = 0; i < SHA256_DIGEST_LENGTH; i++)
           sprintf(&mdString[i*2], "%02x", (unsigned int)digest[i]);
   
       printf("SHA256 digest: %s\n", mdString);
   
   
       return 0;
   }

2. Let’s try to compile both sample cpp files and you should observe the following output screenshot.
   ~$ gcc sha256_sample1.cpp -o sample1 -lcrypto
   ~$ ./sample1
   SHA256 digest: b94d27b9934d3e08a52e52d7da7dabfac484efe37a5380ee9088f7ace2efcde9
   ~$ gcc sha256_sample2.cpp -o sample2 -lcrypto
   ~$ ./sample2
   SHA256 digest: b94d27b9934d3e08a52e52d7da7dabfac484efe37a5380ee9088f7ace2efcde9
   Note: -lcrypto will include the crypto library from openssl