Removing difference between CLI and FFI use for computing a message digest

[Matt Caswell]

On 15/09/2020 22:48, Sage Gerard wrote:
> I have a Racket program that uses libcrypto through FFI bindings to
> compute digests. It's wrong because it returns different answers than
> `openssl dgst`,regardless of hash algorithm.
> 
> The code is here:
> https://github.com/zyrolasting/xiden/blob/libcrypto/openssl.rkt#L76
> It is based on the example in:
> https://wiki.openssl.org/index.php/EVP_Message_Digests.
> 
> I'm not expecting anyone to run this program or review Racket code in
> detail. The links are just there for context. I just want to know if
> there are common C-level mistakes libcrypto users make that would make
> their digests disagree with the CLI. As far as I can tell, I replicated
> the example on wiki.openssl.org well enough to deterministically compute
> a digest with any byte string.
> 
> Let me know if there is any other context I can provide.

Common "rookie" errors that spring to mind are:

1) Use strlen on binary data and end up passing the wrong length of data
to the functions.

2) Include carriage return/line feed in the input data in one context
but not in another.

Matt