* * * * *

                         The OpenSSL/LibreSSL shuffle

Two and a half years ago, someone tried using my UUID (Universally Unique
Identifier) library with a modern version of OpenSSL (Secure Socket Layer)
[1]. At the time I rejected the patch because I couldn't use it (I was, and
still am, using an older version of OpenSSL). Then today, I was notified that
someone else tried to do the same [2], and I figured it was time to actually
adress the issue.

It used to be that you could do:

-----[ C ]-----
#include <openssl/evp.h>

unsigned char hash[EVP_MAX_MD_SIZE];
EVP_MD_CTX    ctx;

EVP_DigestInit(&ctx,EVP_md5());
EVP_DigestUpdate(&ctx,data,len);
EVP_DigestFinal(&ctx,hash,&hashsize);
-----[ END OF LINE ]-----

The context variable declaration changed and you no longer could do that.
Instead, you now have to:

-----[ C ]-----
#include <openssl/evp.h>

unsigned char  hash[EVP_MAX_MD_SIZE];
EVP_MD_CTX    *ctx;

ctx = EVP_MD_CTX_new();
if (ctx != NULL)
{
 EVP_DigestInit(ctx,EVP_md5());
 EVP_DigestUpdate(ctx,data,len);
 EVP_DigestFinal(ctx,hash,&hashsize);
 EVP_MD_CTX_free(ctx);
}
-----[ END OF LINE ]-----

It's an annoying change and yet, I can understand why the change was made—
future updates of hash functions could use more space than what you
statically allocate which could lead to a buffer overrun. It also changed
what used to be an error-free path (well, buffer overruns aside) to a path
that could fail. The reason I put off making the change was trying to find
the version of OpenSSL where the change was made. After downloading over a
dozen versions of OpenSSL and checking each one, I found the change in
version 1.1.0.

This also prompted me to spend the time to update my TLS (Transport Layer
Security) Lua module [3] to the latest version. This also involved
downloading over a dozen versionf of LibreSSL and checking each one. There
was only one minor change involved, and that was adding a new call to the
module.

I have yet to profile LibreSSL [4] though.

[1] https://github.com/spc476/SPCUUID/pull/3
[2] https://github.com/spc476/SPCUUID/issues/4
[3] https://github.com/spc476/lua-conmanorg/blob/master/src/tls.c
[4] gopher://gopher.conman.org/0Phlog:2020/12/28.1

Email author at [email protected]