1 reason that MAPM was chosen for the .bigfloat functions was that it could be compiled by the compiler that mIRC uses, and I'm wondering if Schannel can do that, and whether it still supports the various OS that mIRC runs on. Any switch-over would need to continue compatibility with OpenSSL, because I'm pretty sure that's what the IRC networks are using.
I'm not sure how the TLS is used in IRC, but I know that servers often blow off a lot of the RSA settings for the certificate you create in options/ssl, but that are considered important elsewhere.
For example, there are only a few networks like Libera.Chat that reject your certificate if it's expired, while the rest of them keep letting you use it for SASL. The RSA public exponent is usually 65537, but NIST guidelines says it's OK if it's as large as 2^256. But OpenSSL rejects if it's larger than 2^64, except when you use a small enough key.
The IRC servers don't even check the signature on your self-signed client.pem certificate. You can generate a certificate, then use notepad to alter without inserting or deleting one of the mime digits near the tail end of the public key, where the signature is located, and that ruins the signature and changes the fingerprint. But all the IRC servers will accept this certificate for SASL as long as you add the new fingerprint to nickserv.
One of the reasons that OpenSSL has more bugs is it's a larger bag of features so there's more that can go wrong, and I'm of the understanding that most of the time these problems don't affect the things that mIRC uses.
I get the impression that switching over from 1.1.1 to 3.0 would require a lot of coding, and some things are no longer even available, as they keep on shifting things into optional 'legacy' features. It was only v7.56 that did the upgrade from 1.0.x to 1.1.1
v3.0 has also started doing sneaky things by continuing to support legacy syntax parameters then ignoring them. Or, they change an external function to use a different internal function that's more secure, and they won't offer a way to get the old functionality if you really want to keep it. There are quite a few valid commands in 1.1.1's command line interface that are valid, but won't work in 3.0
For example, when testing a number to see if it's a prime, OpenSSL had several external functions, and one of them that was fairly quick - was suddenly switched over to using Miller-Rabin, which caused a DLL to suddenly take a LONG time to initialize when loading.
Miller-Rabin can't really prove something is a prime, it just detects most non-primes as not being primes, and by repeating the test multiple times it can increase the confidence that a number isn't a non-prime that happened to pass the test(s). In 1.1.1 the external function lets you specify how many times you wanted to repeat the test before it declares the number is probably prime because it passed all the tests. You could even tell it to just make 1 test against the number, which would reject the vast majority of non-primes. The claim for Miller-Rabin is that the chance of it being wrong is 1/(2^number of tests), but when OpenSSL generates primes for RSA, it rarely finds a number that passes round#1 then fails any other test. When searching and finding thousands of safe primes, I have yet to find any cases where the p and q both passed 1 round but it then turned out that either p or q failed additional rounds because of not being primes.
Well, for v3.0 they decided that it wasn't secure if programs tested using just 1 round, so they modified the external function call so that it ignored the parameter specifying the number of tests if it's less than the number of rounds they think you should use, because they decided that there's no valid reason to test fewer than the minimum they decide. And, by doing things like this, they would allow programs to swap in new OpenSSL modules without needing to change their source code where they invoke the OpenSSL code, even though their sneaky changes causes OpenSSL to no longer behave like it used to.
Well there is at least 1 valid reason to use just 1 round of Miller-Rabin, which is when trying to find a safe prime. That's where you are trying to find 2 numbers p and q, where p=2*q+1, and both p and q are primes. So there's no point in wasting time doing more than 1 round against 'p' without first checking to see if 'q' can pass even ONE round. So when using 1.1.1 you can check 1 round against 'p' before doing the extra rounds against 'q', then come back to 'p' to do the additional tests skipped earlier. But when using 3.0, they make you do the whole 128 rounds against 'p' before letting you test 'q' even though more than 99% of the q's won't ever pass more than 1 round.