Creating ECDSA keys with OpenSSL 3 (migration problem) - c++

Question

I need to create ECDSA keys and used old OpenSSL code until now, which dosn't compile any more under OpenSSL3, there are now lots of deprecation errors. I invested now several days with search & try, but I can't solve it. I am trying the simple example [https://fm4dd.com/openssl/eckeycreate.shtm][1], but already the first lines create these errors:
WorkerThread.cpp(34,2): error C4996: 'ERR_load_BIO_strings': Since OpenSSL 3.0
WorkerThread.cpp(47,19): error C4996: 'EC_KEY_new_by_curve_name': Since OpenSSL 3.0
WorkerThread.cpp(54,2): error C4996: 'EC_KEY_free': Since OpenSSL 3.0
So the first idea would be to eliminate these compiler errors somehow. I found the switches
#define OPENSSL_API_COMPAT 30000
#define OPENSSL_NO_DEPRECATED
but they create even more errors, because now suddenly even the EC_KEY is unknown to the compiler. No solution.
So there stays the hard way to try to migrate the code somehow to OpenSSL3, because there seems to be no example code in the whole internet for simply creating an ECDSA key with OpenSSL3, and extract the private and public part. But just changing single functions with an OpenSSL3 matching function doesn't solve it, because the whole concept changes (switching from low level API to high level, with a completely different programming model).
I have tried fiddling around with lots of examples, but it looks like my programming task that seems so simple is a very complicated thing. Any help is appreciated, but I want to stay in C/C++ because my application is performance critical.
Environment: MS Win10, MS Visual Studio 2019, latest OpenSSL 3
[1]: https://fm4dd.com/openssl/eckeycreate.shtm

Answer 1

WorkerThread.cpp(34,2): error C4996: 'ERR_load_BIO_strings': Since OpenSSL 3.0
You don't need to call any of those initialisation functions. Just remove them from your code. They are not needed with any version of OpenSSL from 1.1.0 onwards.
In the example, all of the code for getting an EC_GROUP, creating an EC_KEY, generating a key, setting the OPENSSL_EC_NAMED_CURVE flag and assigning it to an EVP_PKEY can be completely removed. Replace it with a simple call to EVP_EC_gen(). See the man page here:
https://www.openssl.org/docs/man3.0/man3/EVP_EC_gen.html
E.g. all of that code can be replaced with something like
pkey = EVP_EC_gen("secp521r1");
if (pkey == NULL) {
BIO_printf(outbio, "Error generating the ECC key.");
abort();
}