How to Generate SHA256 Hashes with OpenSSL and C : A Solution for Missing Functions?

Generating SHA256 Hashes with OpenSSL and C

When tasked with creating a hash using SHA256 with OpenSSL and C , understanding the library's capabilities becomes crucial. One such instance encountered an issue with missing OpenSSL functions despite including the necessary header files and build paths. The following code snippet illustrates the solution:

<code class="cpp">void sha256_hash_string(unsigned char hash[SHA256_DIGEST_LENGTH], char outputBuffer[65]) {
  int i = 0;
  for (i = 0; i < SHA256_DIGEST_LENGTH; i++) {
    sprintf(outputBuffer + (i * 2), "%02x", hash[i]);
  }
  outputBuffer[64] = 0;
}

void sha256_string(char *string, char outputBuffer[65]) {
  unsigned char hash[SHA256_DIGEST_LENGTH];
  SHA256_CTX sha256;
  SHA256_Init(&sha256);
  SHA256_Update(&sha256, string, strlen(string));
  SHA256_Final(hash, &sha256);
  int i = 0;
  for (i = 0; i < SHA256_DIGEST_LENGTH; i++) {
    sprintf(outputBuffer + (i * 2), "%02x", hash[i]);
  }
  outputBuffer[64] = 0;
}

int sha256_file(char *path, char outputBuffer[65]) {
  FILE *file = fopen(path, "rb");
  if (!file) return -534;
  unsigned char hash[SHA256_DIGEST_LENGTH];
  SHA256_CTX sha256;
  SHA256_Init(&sha256);
  const int bufSize = 32768;
  unsigned char *buffer = malloc(bufSize);
  int bytesRead = 0;
  if (!buffer) return ENOMEM;
  while ((bytesRead = fread(buffer, 1, bufSize, file))) {
    SHA256_Update(&sha256, buffer, bytesRead);
  }
  SHA256_Final(hash, &sha256);
  sha256_hash_string(hash, outputBuffer);
  fclose(file);
  free(buffer);
  return 0;
}</code>

To utilize this code, follow these steps:

<code class="cpp">static unsigned char buffer[65];
sha256("string", buffer);
printf("%s\n", buffer);</code>

This approach effectively generates SHA256 hashes using OpenSSL and C , resolving the include path issue encountered earlier.

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