Howto base64 encode with C/C++ and OpenSSL

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 OpenSSL.

[code lang=”c”]


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);

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_get_mem_ptr(b64, &bptr);

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


return buff;

And to compile this just use the following command:

cc -o base64 base64.c -lssl

11 thoughts on “Howto base64 encode with C/C++ and OpenSSL

  1. ChaosCreator

    thanks for the code , but can you try to compile your code next time before you release it ????

  2. carson Post author

    Sorry about that. I believe somewhere along the line an upgrade to the blog software converted some of the code into html. It should be good now.

  3. Pingback: Howto base64 decode with C/C++ and OpenSSL @ IONCANNON

  4. Antonio

    I tested your program and it good i like.
    Do you have one example to sign a document with openSSL ?


  5. Subra

    Hey Carson,

    Thanks for the code. But do you have any idea as to why ur function base64 adds a newline (‘\n’) character at the end of the string.

    Similarly, ut base64 decode function expects a newline character at the end.


  6. Amit

    Hi Subra,

    base64 algorithm in itself appends a carriage return and linefeed characters after its ‘linesize’ character and at the end of the test to be encoded. This infact increases the length of the encoded string by about 3%, but this cannot be avoided.

  7. Jon Scobie

    I think you’ll find that you should be using strlen(“YOYO!”) not sizeof as that will return a completely different answer. If you test with “uuencode -m” or “openssl enc” you will see what I mean.

  8. Bill

    ** returns the length of the b64 decoded buffer, outbuf is set to a pointer
    ** to new memory containing the result. This will be null terminated with
    ** an extra byte.
    ** Caller must free the returned string pointed to in outbuf.
    int base64d(const unsigned char *input, int length, char **outbuf) {

    BIO *bio, *b64, *bmem, *decoder;
    char inbuf[512];
    int inlen, readlen = -1;
    BUF_MEM *bptr;
    char * buffer;

    bmem = BIO_new_mem_buf(input, length);
    b64 = BIO_new(BIO_f_base64());
    /* decoder = BIO_new(BIO_s_mem()); */

    decoder = BIO_push(b64, bmem);
    /* BIO_push(decoder, b64); */

    BIO_get_mem_ptr(decoder, &bptr);

    if (buffer = (char *)malloc(length)) {
    readlen = BIO_read(decoder, buffer, length);
    buffer[readlen] = 0;


    *outbuf = buffer;
    return readlen;

  9. trulyliu

    There is a minor mistake in your code:

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

Comments are closed.