> From: owner-openssl-us...@openssl.org On Behalf Of Craig
> Sent: Monday, 21 November, 2011 11:56
> I'm fairly new to C/C++ so please bear with me.
Warning: beware of people who tell you C++ is a superset of C.
It's not. C++, deliberately, includes MOST of C -- maybe
80-90%, depending how you count -- but NOT all. So in some
cases it matters which you are using.
> I'm having issues base64 decoding files that have been
> encrypted using AES-256-CBC and the base64 encoded. I'm
> using the following code to base64 decode and this works
> fine on "plain text" files that have been base64 encoded.
> char * base64Decode(unsigned char * input, int length) {
> BIO *b64, *bmem;
> char * buffer = (char *) malloc(length);
> memset(buffer, 0, length);
> b64 = BIO_new(BIO_f_base64());
> bmem = BIO_new_mem_buf(input, length);
> bmem = BIO_push(b64, bmem);
> BIO_read(bmem, buffer, length);
> BIO_free_all(bmem);
> return buffer;
> }
Nit: the cast on malloc is not needed in correct C
(if your compiler complains, you didn't #include <stdlib.h>
and just throwing in a cast is NOT the correct solution);
in C++ it is better to use 'new' and 'delete' instead
(which don't need any casts).
Note that a base64 decoded result will ALWAYS be smaller
than the input, so malloc'ing for length is more than
you actually need. However, the computation of exactly
what you need can be a little tricky, and usually it's
better to err on the side of too much than too little.
> The returned char is always much smaller than expeted for
> files that have been encrypted. I do pass the correct encoded
> data size along with the data
What makes you think it's smaller? Are you trying to treat
the decoded but still encrypted data as a C string? It's not.
It's raw binary data that usually and in your case contains
'null' characters (byte value zero) which terminate a string.
With modern (>WW2) ciphers even unencrypted/clear data CAN be
any binary data, although you may choose in your application(s)
to encrypt only C strings, or only printable ones.
The return value from BIO_read is the number of bytes read,
which for BIO_f_base64 is the number of bytes decoded, or
negative for error. Check and use that.
If you are using C++, you CAN put binary data in a std::string,
which is NOT the same as a C OR C++ char* string. There is
no standard or builtin way, in either language, to return a
pointer (char*) plus count together. You can:
- pass the (already-allocated) buffer and return the length
- return the newly-allocated pointer and store the length
"to" an argument (that is, through a pointer argument)
- return the length and store the newly-allocated pointer
"to" an argument
- return an error code/status, or nothing, and store both
length and newly-allocated pointer "to" arguments
- return a struct you declare containing pointer and length
- store "to" an argument struct ditto
- more complicated possibilities
<snip rest>
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