From 3cd3c27c99393af12d40949f2b40e44ac768c338 Mon Sep 17 00:00:00 2001 From: Theo Buehler Date: Tue, 11 Apr 2023 19:43:49 +0200 Subject: [PATCH] Fix modular square root test with LibreSSL >= 3.8 [ This is a backport to the 3.1 branch. ] If x is a modular square root of a (mod p) then so is (p - x). Both answers are valid. In particular, both 2 and 3 are valid square roots of 4 (mod 5). Do not assume that a particular square root is chosen by the algorithm. Indeed, the algorithm in OpenSSL and LibreSSL <= 3.7 returns a non-deterministic answer in many cases. LibreSSL 3.8 and later will always return the smaller of the two possible answers. This breaks the current test case. Instead of checking for a particular square root, check that the square of the claimed square root is the given value. This is always true. Add the simplest test case where the answer is indeed non-deterministic. (cherry picked from commit 93548ae9597ba40d3f8b564f6a948ce55b432e30) --- test/openssl/test_bn.rb | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/test/openssl/test_bn.rb b/test/openssl/test_bn.rb index 77af14091..ea88ff06c 100644 --- a/test/openssl/test_bn.rb +++ b/test/openssl/test_bn.rb @@ -175,7 +175,9 @@ def test_mod_sqr end def test_mod_sqrt - assert_equal(3, 4.to_bn.mod_sqrt(5)) + assert_equal(4, 4.to_bn.mod_sqrt(5).mod_sqr(5)) + # One of 189484 or 326277 is returned as a square root of 2 (mod 515761). + assert_equal(2, 2.to_bn.mod_sqrt(515761).mod_sqr(515761)) assert_equal(0, 5.to_bn.mod_sqrt(5)) assert_raise(OpenSSL::BNError) { 3.to_bn.mod_sqrt(5) } end