Base64 encoding and decoding using OpenSSL

b64_encode_decode.c

// Encodes Base64
#include <openssl/bio.h>
#include <openssl/buffer.h>
#include <openssl/evp.h>
#include <stdint.h>
// Decodes Base64
#include <assert.h>
#include <openssl/bio.h>
#include <openssl/evp.h>
#include <stdint.h>
#include <stdio.h>
#include <string.h>

/* must be freed by caller */
char *base64_decode(char *b64message, int *dst_len) {
  BIO *bmem = BIO_new(BIO_s_mem());
  BIO *b64 = BIO_new(BIO_f_base64());
  BUF_MEM *buf_mem;
  BIO_push(b64, bmem);
  BIO_puts(b64, b64message);
  BIO_flush(b64);
  BIO_get_mem_ptr(bmem, &buf_mem);
  BIO_set_close(bmem, BIO_NOCLOSE);
  BIO_free_all(b64);
  *dst_len = buf_mem->length;
  return strndup(buf_mem->data, buf_mem->length);
}

char *base64_encode(const char *buffer, size_t buffer_len) {
  BIO *bmem = BIO_new(BIO_s_mem());
  BIO *b64 = BIO_new(BIO_f_base64());
  BUF_MEM *buf_mem;

  b64 = BIO_new(BIO_f_base64());
  bmem = BIO_new(BIO_s_mem());
  BIO_push(bmem, b64);
  BIO_write(bmem, buffer, buffer_len);
  BIO_flush(bmem);
  BIO_get_mem_ptr(b64, &buf_mem);
  BIO_set_close(b64, BIO_NOCLOSE);
  BIO_free_all(b64);
  return strndup(buf_mem->data, buffer_len);
}

int main() {
  // Encode To Base64
  char *base64_encode_output, *text = "pas1";

  base64_encode_output = base64_encode(text, strlen(text));
  printf("Output (base64): %s\n", base64_encode_output);

  // Decode From Base64

  int len;
  char *base64_decode_output = base64_decode("SGVsbG8gV29ybGQ=", &len);
  printf("Output: %s\n", base64_decode_output);
  return 0;
}

Based on OpenSSL Base64 Encoding: Binary Safe and Portable

Changes:

• simplefied API
• no need to manually calculate output length

Duplicated new in base64_encode:

  b64 = BIO_new(BIO_f_base64());
  bmem = BIO_new(BIO_s_mem());