Question

I use the code below where I use BIO_read from an in-memory-buffer to do base64 decoding. Sometimes BIO_read returns 0 for the size parameter. I could not yet figure out why that would be happening. Any Ideas?

static std::vector<unsigned char> base64_decode(void *input, int length)
{
    std::vector<unsigned char> result(length, 0);
    BIO *b64, *bmem;

    b64 = BIO_new(BIO_f_base64());
    bmem = BIO_new_mem_buf(input, length);
    bmem = BIO_push(b64, bmem);

    int size = BIO_read(bmem, &result[0], length);
    if (size == 0)
        fprintf(stderr, "Problem\n");
    result.resize(size);

    BIO_free_all(bmem);

    return result;
}

Answer 1

I had similar issues with base64 decoding until I understood that base64 can be formatted with newlines or not.

You should try to normalize your input by removing newline characters and then setting the OpenSSL BIO_FLAGS_BASE64_NO_NL flag on your b64 BIO (see the OpenSSL documentation on b64 BIO).