pkey/ec: deprecate OpenSSL::PKey::EC::Point#mul(ary, ary [, bn])

Deprecate it for future removal. However, I do not expect any
application is affected by this.

The other form of calling it, PKey::EC::Point#mul(bn [, bn]) remains
untouched.

PKey::EC::Point#mul calls EC_POINTs_mul(3) when multiple BNs
are given as an array. LibreSSL 2.8.0 released on 2018-08 removed the
feature and OpenSSL 3.0 which is planned to be released in 2020 will
also deprecate the function as there is no real use-case.

ext/openssl/ossl_pkey_ec.c

@@ -1505,6 +1505,10 @@ static VALUE ossl_ec_point_mul(int argc, VALUE *argv, VALUE self)
 	if (EC_POINT_mul(group, point_result, bn_g, point_self, bn, ossl_bn_ctx) != 1)
 	    ossl_raise(eEC_POINT, NULL);
     } else {
+#if OPENSSL_VERSION_MAJOR+0 >= 3 || defined(LIBRESSL_VERSION_NUMBER)
+        rb_raise(rb_eNotImpError, "calling #mul with array arguments is not" \
+                 "supported by this OpenSSL version");
+#else
 	/*
 	 * bignums | arg1[0] | arg1[1] | arg1[2] | ...
 	 * points  | self    | arg2[0] | arg2[1] | ...
@@ -1519,6 +1523,9 @@ static VALUE ossl_ec_point_mul(int argc, VALUE *argv, VALUE self)
 	if (RARRAY_LEN(arg1) != RARRAY_LEN(arg2) + 1) /* arg2 must be 1 larger */
 	    ossl_raise(rb_eArgError, "bns must be 1 longer than points; see the documentation");
 
+        rb_warn("OpenSSL::PKey::EC::Point#mul(array, array) is deprecated; " \
+                "use #mul(bn) form instead");
+
 	num = RARRAY_LEN(arg1);
 	bns_tmp = rb_ary_tmp_new(num);
 	bignums = ALLOCV_N(const BIGNUM *, tmp_b, num);
@@ -1544,6 +1551,7 @@ static VALUE ossl_ec_point_mul(int argc, VALUE *argv, VALUE self)
 
 	ALLOCV_END(tmp_b);
 	ALLOCV_END(tmp_p);
+#endif
     }
 
     return result;

test/openssl/test_pkey_ec.rb

@@ -349,21 +349,26 @@ def test_ec_point_mul
       # 3 * (6, 3) + 3 * (5, 1) = (7, 6)
       result_a2 = point_a.mul(3, 3)
       assert_equal B(%w{ 04 07 06 }), result_a2.to_octet_string(:uncompressed)
-      # 3 * point_a = 3 * (6, 3) = (16, 13)
-      result_b1 = point_a.mul([3], [])
-      assert_equal B(%w{ 04 10 0D }), result_b1.to_octet_string(:uncompressed)
-      # 3 * point_a + 2 * point_a = 3 * (6, 3) + 2 * (6, 3) = (7, 11)
-      begin
+      EnvUtil.suppress_warning do # Point#mul(ary, ary [, bn]) is deprecated
+        begin
+          result_b1 = point_a.mul([3], [])
+        rescue NotImplementedError
+          # LibreSSL and OpenSSL 3.0 do no longer support this form of calling
+          next
+        end
+
+        # 3 * point_a = 3 * (6, 3) = (16, 13)
+        result_b1 = point_a.mul([3], [])
+        assert_equal B(%w{ 04 10 0D }), result_b1.to_octet_string(:uncompressed)
+        # 3 * point_a + 2 * point_a = 3 * (6, 3) + 2 * (6, 3) = (7, 11)
         result_b1 = point_a.mul([3, 2], [point_a])
-      rescue OpenSSL::PKey::EC::Point::Error
-        # LibreSSL doesn't support multiple entries in first argument
-        raise if $!.message !~ /called a function you should not call/
-      else
         assert_equal B(%w{ 04 07 0B }), result_b1.to_octet_string(:uncompressed)
+        # 3 * point_a + 5 * point_a.group.generator = 3 * (6, 3) + 5 * (5, 1) = (13, 10)
+        result_b1 = point_a.mul([3], [], 5)
+        assert_equal B(%w{ 04 0D 0A }), result_b1.to_octet_string(:uncompressed)
+
+        assert_raise(ArgumentError) { point_a.mul([1], [point_a]) }
       end
-      # 3 * point_a + 5 * point_a.group.generator = 3 * (6, 3) + 5 * (5, 1) = (13, 10)
-      result_b1 = point_a.mul([3], [], 5)
-      assert_equal B(%w{ 04 0D 0A }), result_b1.to_octet_string(:uncompressed)
     rescue OpenSSL::PKey::EC::Group::Error
       # CentOS patches OpenSSL to reject curves defined over Fp where p < 256 bits
       raise if $!.message !~ /unsupported field/
@@ -376,7 +381,6 @@ def test_ec_point_mul
     # invalid argument
     point = p256_key.public_key
     assert_raise(TypeError) { point.mul(nil) }
-    assert_raise(ArgumentError) { point.mul([1], [point]) }
     assert_raise(TypeError) { point.mul([1], nil) }
     assert_raise(TypeError) { point.mul([nil], []) }
   end