Add OpenSSL.secure_compare with same semantics as Active Support >= 5.2

secure_compare is for user input, fixed_length_secure_compare for already processed data that is known to have the same length

2 files changed, 31 insertions, 0 deletions

diff --git a/lib/openssl.rb b/lib/openssl.rb
index 09142829..47a8fc49 100644
--- a/lib/openssl.rb
+++ b/lib/openssl.rb
@@ -20,3 +20,17 @@ require 'openssl/digest'
 require 'openssl/x509'
 require 'openssl/ssl'
 require 'openssl/pkcs5'
+
+module OpenSSL
+  # call-seq:
+  #   OpenSSL.secure_compare(string, string) -> boolean
+  #
+  # Constant time memory comparison. Inputs are hashed using SHA-256 to mask
+  # the length of the secret. Returns +true+ if the strings are identical,
+  # +false+ otherwise.
+  def self.secure_compare(a, b)
+    hashed_a = OpenSSL::Digest::SHA256.digest(a)
+    hashed_b = OpenSSL::Digest::SHA256.digest(b)
+    OpenSSL.fixed_length_secure_compare(hashed_a, hashed_b) && a == b
+  end
+end
diff --git a/test/test_ossl.rb b/test/test_ossl.rb
index 85363cb5..394f30e0 100644
--- a/test/test_ossl.rb
+++ b/test/test_ossl.rb
@@ -26,6 +26,23 @@ class OpenSSL::OSSL < OpenSSL::SSLTestCase
     assert_raises(ArgumentError) { OpenSSL.fixed_length_secure_compare("aaa", "bbbb") }
   end
 
+  def test_secure_compare
+    refute OpenSSL.secure_compare("aaa", "a")
+    refute OpenSSL.secure_compare("aaa", "aa")
+
+    assert OpenSSL.secure_compare("aaa", "aaa")
+
+    refute OpenSSL.secure_compare("aaa", "aaaa")
+    refute OpenSSL.secure_compare("aaa", "baa")
+    refute OpenSSL.secure_compare("aaa", "aba")
+    refute OpenSSL.secure_compare("aaa", "aab")
+    refute OpenSSL.secure_compare("aaa", "aaab")
+    refute OpenSSL.secure_compare("aaa", "b")
+    refute OpenSSL.secure_compare("aaa", "bb")
+    refute OpenSSL.secure_compare("aaa", "bbb")
+    refute OpenSSL.secure_compare("aaa", "bbbb")
+  end
+
   def test_memcmp_timing
     # Ensure using fixed_length_secure_compare takes almost exactly the same amount of time to compare two different strings.
     # Regular string comparison will short-circuit on the first non-matching character, failing this test.