EC_GROUP_get_curve_name() returns NID_undef when OpenSSL does not
recognize the curve and there is no associated OID.

Handle this case explicitly and return nil instead of the string
"UNDEF", which should not be exposed outside the extension.

https://github.com/ruby/openssl/commit/2c16821c07

Remove the following subclasses of OpenSSL::PKey::PKeyError and make
them aliases of it.

 - OpenSSL::PKey::DHError
 - OpenSSL::PKey::DSAError
 - OpenSSL::PKey::ECError
 - OpenSSL::PKey::RSAError

Historically, methods defined on OpenSSL::PKey and OpenSSL::PKey::PKey
raise OpenSSL::PKey::PKeyError, while methods on the subclasses raise
their respective exception classes. However, this distinction is not
particularly useful since all those exception classes represent the
same kind of errors from the underlying EVP_PKEY API.

I think this convention comes from the fact that OpenSSL::PKey::{DH,
DSA,RSA} originally wrapped the corresponding OpenSSL structs DH, DSA,
and RSA, before they were unified to wrap EVP_PKEY, way back in 2002.

OpenSSL::PKey::EC::Group::Error and OpenSSL::PKey::EC::Point::Error
are out of scope of this change, as they are not subclasses of
OpenSSL::PKey::PKeyError and do not represent errors from the EVP_PKEY
API.

https://github.com/ruby/openssl/commit/e74ff3e272

Raise ArgumentError if this is attempted when the extension is compiled
with OpenSSL 3.0 or later. The form will be fully removed when we drop
support for OpenSSL 1.1.1.

When OpenSSL::PKey::{DH,DSA,EC,RSA}.new is called without any arguments,
it sets up an empty corresponding low-level struct and wraps it in an
EVP_PKEY. This is useful when the user later fills the missing fields
using low-level setter methods such as OpenSSL::PKey::RSA#set_key.

Such setter methods are not compatible with OpenSSL 3.0 or later, where
EVP_PKEY is immutable once created. This means that the ability to
create an empty instance is useless.

https://github.com/ruby/openssl/commit/affd569f78

In OpenSSL's master branch, importing/loading a key in the FIPS mode
automatically performs a pair-wise consistency check. This breaks tests
for OpenSSL::PKey::EC#check_key and DH#params_ok? as they use
deliberately invalid keys. These methods would not be useful in the
FIPS mode anyway.

Fixes https://github.com/ruby/openssl/issues/926

https://github.com/ruby/openssl/commit/25ad8f4bdb

https://github.com/ruby/openssl/commit/65c5a772ea

EVP_DigestVerify in OpenSSL returns 0 to indicate a signature
verification failure and can return -1  to indicate other
failures, such as invalid ASN1 contents. ruby/openssl also
reflects that by returning false with 0 and raising an error
with -1.
EVP_DigestVerify in AWS-LC simply returns 0 for any failure.

https://github.com/ruby/openssl/commit/be8ba76dc1

OpenSSL allows invalid EC keys or DH params to be parsed. The consuming
application can then run parameter/key checks to check the validity of
the parameters. We happen to run tests to verify that this behaves as
expected.
AWS-LC on the other hand, directly raises an error and disallows the
invalid state to be parsed, rather than making it parsable and checking
the validity later. Relevant tests have been adjusted accordingly to
reflect this.

https://github.com/ruby/openssl/commit/febe50be1b

The method has two forms, each corresponding to EC_POINT_mul() and
EC_POINTs_mul(). The latter form does not work with any OpenSSL or
LibreSSL versions that are still supported by upstream.

The latter form has an extremely confusing behavior, too, and using it
would print a deprecation warning since commit https://github.com/ruby/openssl/commit/812de4253d25 in 2020,
which went to 3.0.0. Let's remove it.

https://github.com/ruby/openssl/commit/7343d3c559

test/openssl/fixtures/pkey/p256_too_large.pem and p384_invalid.pem are
invalid keys where the encoded public key doesn't match the private key.
They are only useful for test cases for OpenSSL::PKey::EC#check_key and
will not be reused elsewhere. Let's directly include the PEM encoding
as a heredoc for clarity.

p384_invalid.pem is dropped because it is redundant.

https://github.com/ruby/openssl/commit/2f807ff30f

https://github.com/ruby/openssl/commit/d07183f639