How to Calculate the MD5 Hash of a File in C using OpenSSL?

Calculating MD5 Hash from a File in C

In scenarios where safeguarding data integrity is critical, the MD5 hash algorithm plays a vital role. To compute the MD5 hash of a file in C , here's a robust implementation utilizing OpenSSL:

Implementation:

#include <fstream>
#include <openssl/md5.h>

int main() {
  // Open the file
  std::ifstream file("input_file.txt");

  // Create a buffer to store the file contents
  std::vector<char> buffer(std::istreambuf_iterator<char>(file), {});

  // Calculate the MD5 hash
  unsigned char hash[MD5_DIGEST_LENGTH];
  MD5((unsigned char*) buffer.data(), buffer.size(), hash);

  // Convert the hash to a string
  std::stringstream ss;
  for (int i = 0; i < MD5_DIGEST_LENGTH; i++) {
    ss << std::hex << std::setfill('0') << std::setw(2) << (int) hash[i];
  }
  std::string md5_hash = ss.str();

  // Print the MD5 hash
  std::cout << "MD5 hash: " << md5_hash << std::endl;

  return 0;
}

This implementation opens the file, reads its contents into a buffer, and calculates the MD5 hash using the OpenSSL library. The hash is then converted to a hexadecimal string and displayed.

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