[ruby/openssl] pkey/dh: use high level EVP interface to generate parameters and keys

Implement PKey::DH.new(size, gen), PKey::DH.generate(size, gen), and
PKey::DH#generate_key! using PKey.generate_parameters and .generate_key
instead of the low level DH functions.

Note that the EVP interface can enforce additional restrictions - for
example, DH key shorter than 2048 bits is no longer accepted by default
in OpenSSL 3.0. The test code is updated accordingly.

c2e9b16f0b

test/openssl/test_pkey_dh.rb

@@ -4,12 +4,19 @@ require_relative 'utils'
 if defined?(OpenSSL) && defined?(OpenSSL::PKey::DH)
 
 class OpenSSL::TestPKeyDH < OpenSSL::PKeyTestCase
-  NEW_KEYLEN = 256
+  NEW_KEYLEN = 2048
 
-  def test_new
+  def test_new_empty
+    dh = OpenSSL::PKey::DH.new
+    assert_equal nil, dh.p
+    assert_equal nil, dh.priv_key
+  end
+
+  def test_new_generate
+    # This test is slow
     dh = OpenSSL::PKey::DH.new(NEW_KEYLEN)
     assert_key(dh)
-  end
+  end if ENV["OSSL_TEST_ALL"]
 
   def test_new_break
     assert_nil(OpenSSL::PKey::DH.new(NEW_KEYLEN) { break })
@@ -80,7 +87,7 @@ class OpenSSL::TestPKeyDH < OpenSSL::PKeyTestCase
   end
 
   def test_dup
-    dh = OpenSSL::PKey::DH.new(NEW_KEYLEN)
+    dh = Fixtures.pkey("dh1024")
     dh2 = dh.dup
     assert_equal dh.to_der, dh2.to_der # params
     assert_equal_params dh, dh2 # keys