How to create a md5 hash of a string in C?

Question

I\'ve found some md5 code that consists of the following prototypes...

I\'ve been trying to find out where I have to put the string I want to hash, what functions I

Answer 1

All of the existing answers use the deprecated MD5Init(), MD5Update(), and MD5Final().

Instead, use EVP_DigestInit_ex(), EVP_DigestUpdate(), and EVP_DigestFinal_ex(), e.g.

// example.c
//
// gcc example.c -lssl -lcrypto -o example

#include 
#include 
#include 

void bytes2md5(const char *data, int len, char *md5buf) {
  // Based on https://www.openssl.org/docs/manmaster/man3/EVP_DigestUpdate.html
  EVP_MD_CTX *mdctx = EVP_MD_CTX_new();
  const EVP_MD *md = EVP_md5();
  unsigned char md_value[EVP_MAX_MD_SIZE];
  unsigned int md_len, i;
  EVP_DigestInit_ex(mdctx, md, NULL);
  EVP_DigestUpdate(mdctx, data, len);
  EVP_DigestFinal_ex(mdctx, md_value, &md_len);
  EVP_MD_CTX_free(mdctx);
  for (i = 0; i < md_len; i++) {
    snprintf(&(md5buf[i * 2]), 16 * 2, "%02x", md_value[i]);
  }
}

int main(void) {
  const char *hello = "hello";
  char md5[33]; // 32 characters + null terminator
  bytes2md5(hello, strlen(hello), md5);
  printf("%s\n", md5);
}