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https://journal.missiondata.com/how-to-base64-encode-with-c-c-and-openssl-acccb1045c42

How To Base64 Encode with C/C++ and OpenSSL

Originally posted April 11, 2006

I’ve been doing a little C programming lately and I have found that if you have a up to date distribution of linux there are a lot of libraries out there that make doing things you do in other languages like java easier.

As I have time I’m going to post some examples of what I have found. The first here is how to base64 encode a chunk of memory using OpenSLL.

#include <string.h>

#include <openssl/sha.h>
#include <openssl/hmac.h>
#include <openssl/evp.h>
#include <openssl/bio.h>
#include <openssl/buffer.h>

char *base64(const unsigned char *input, int length);

int main(int argc, char **argv)
{
  char *output = base64("YOYO!", sizeof("YOYO!"));
  printf("Base64: *%s*\n", output);
  free(output);
}

char *base64(const unsigned char *input, int length)
{
  BIO *bmem, *b64;
  BUF_MEM *bptr;

  b64 = BIO_new(BIO_f_base64());
  bmem = BIO_new(BIO_s_mem());
  b64 = BIO_push(b64, bmem);
  BIO_write(b64, input, length);
  BIO_flush(b64);
  BIO_get_mem_ptr(b64, &bptr);

  char *buff = (char *)malloc(bptr->length);
  memcpy(buff, bptr->data, bptr->length-1);
  buff[bptr->length-1] = 0;

  BIO_free_all(b64);

  return buff;
}

And to compile this just use the following command:

cc -o base64 base64.c -lssl