OpenSSL SHA Hashing Example in C++

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

1. Here are the openssl SHA sample source code.
   
   Example #1: sha_sample1.cpp
   C++

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

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

   
   Example #2: sha_sample2.cpp

   C++

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

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   #include <stdio.h> #include <string.h> #include <openssl/sha.h>   int main() {     unsigned char digest[SHA_DIGEST_LENGTH];     const char* string = "hello world";       SHA_CTX ctx;     SHA_Init(&ctx);     SHA_Update(&ctx, string, strlen(string));     SHA_Final(digest, &ctx);       char mdString[SHA_DIGEST_LENGTH*2+1];     for (int i = 0; i < SHA_DIGEST_LENGTH; i++)         sprintf(&mdString[i*2], "%02x", (unsigned int)digest[i]);       printf("SHA 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 sha_sample1.cpp -o sample1 -lcrypto
   ~$ ./sample1
   SHA digest: 9fce82c34887c1953b40b3a2883e18850c4fa8a6
   ~$ gcc sha_sample2.cpp -o sample2 -lcrypto
   ~$ ./sample2
   SHA digest: 9fce82c34887c1953b40b3a2883e18850c4fa8a6
   Note: -lcrypto will include the crypto library from openssl