Add DHKEM support and test cases

test/openssl/test_pkey.rb

@@ -307,6 +307,52 @@ def test_ml_kem
     assert_equal(shared_secret, privkey.decapsulate(ciphertext))
   end
 
+  def test_dhkem_x25519
+    # DHKEM (RFC 9180) and the X25519/X448 curves are not FIPS-approved; the
+    # KEM is built into the default provider only, not the FIPS module.
+    omit_on_fips
+    # EVP_KEM-X25519 / EVP_KEM-X448 were added in OpenSSL 3.2, but the DHKEM
+    # operation defaults correctly (without an explicit OSSL_KEM_PARAM_OPERATION)
+    # only since OpenSSL 3.5.
+    omit "DHKEM is not supported" unless openssl?(3, 5, 0)
+
+    pkey = OpenSSL::PKey.generate_key("X25519")
+    raw_public_key = pkey.raw_public_key
+    raw_private_key = pkey.raw_private_key
+
+    assert_match(/type_name=X25519/, pkey.inspect)
+    assert_equal(32, raw_public_key.bytesize)  # Npk
+    assert_equal(32, raw_private_key.bytesize) # Nsk
+
+    pubkey = OpenSSL::PKey.new_raw_public_key("X25519", raw_public_key)
+    ciphertext, shared_secret = pubkey.encapsulate
+    assert_equal(32, ciphertext.bytesize)    # Nenc
+    assert_equal(32, shared_secret.bytesize) # Nsecret
+    assert_equal(shared_secret, pkey.decapsulate(ciphertext))
+
+    privkey = OpenSSL::PKey.new_raw_private_key("X25519", raw_private_key)
+    assert_equal(shared_secret, privkey.decapsulate(ciphertext))
+  end
+
+  def test_dhkem_ec
+    # DHKEM (RFC 9180) is built into the default provider only, not the FIPS
+    # module.
+    omit_on_fips
+    # EVP_KEM-EC (RFC 9180 DHKEM over NIST curves) was added in OpenSSL 3.2, but
+    # the DHKEM operation defaults correctly (without an explicit
+    # OSSL_KEM_PARAM_OPERATION) only since OpenSSL 3.5.
+    omit "DHKEM is not supported" unless openssl?(3, 5, 0)
+
+    pkey = OpenSSL::PKey::EC.generate("prime256v1")
+    assert_match(/type_name=EC/, pkey.inspect)
+
+    pubkey = OpenSSL::PKey.read(pkey.public_to_der)
+    ciphertext, shared_secret = pubkey.encapsulate
+    assert_equal(65, ciphertext.bytesize)    # Nenc
+    assert_equal(32, shared_secret.bytesize) # Nsecret
+    assert_equal(shared_secret, pkey.decapsulate(ciphertext))
+  end
+
   def test_raw_initialize_errors
     assert_raise(OpenSSL::PKey::PKeyError) { OpenSSL::PKey.new_raw_private_key("foo123", "xxx") }
     assert_raise(OpenSSL::PKey::PKeyError) { OpenSSL::PKey.new_raw_private_key("ED25519", "xxx") }