cipher: allow setting IV length when using AEAD cipherstopic/cipher-iv-len

Add OpenSSL::Cipher#iv_len=. For interoperability with other
applications, it is sometimes required. Normally 'IV' is fixed-length,
but in OpenSSL, some ciphers such as aes-128-gcm make use of it as
'nonce', which is variable-length.

Changing the IV length in Cipher#iv= is also an option but I decided not
to choose it. Because in Ruby <= 2.3 Cipher#iv= truncates the input when
the length is longer than the current IV length, changing the behavior
might cause unexpected encryption result.

[Bug #8667] [Bug #10420] [GH ruby/ruby#569]

1 files changed, 40 insertions, 0 deletions

diff --git a/test/test_cipher.rb b/test/test_cipher.rb
index ec14f467..dffc0d7b 100644
--- a/test/test_cipher.rb
+++ b/test/test_cipher.rb
@@ -247,6 +247,46 @@ class OpenSSL::TestCipher < OpenSSL::TestCase
       end
     end
 
+    def test_aes_gcm_variable_iv_len
+      pt = "You should all use Authenticated Encryption!"
+      cipher = OpenSSL::Cipher.new("aes-128-gcm").encrypt
+      cipher.key = "x" * 16
+      assert_equal(12, cipher.iv_len)
+      cipher.iv = "a" * 12
+      ct1 = cipher.update(pt) << cipher.final
+      tag1 = cipher.auth_tag
+
+      cipher = OpenSSL::Cipher.new("aes-128-gcm").encrypt
+      cipher.key = "x" * 16
+      cipher.iv_len = 10
+      assert_equal(10, cipher.iv_len)
+      cipher.iv = "a" * 10
+      ct2 = cipher.update(pt) << cipher.final
+      tag2 = cipher.auth_tag
+
+      assert_not_equal ct1, ct2
+      assert_not_equal tag1, tag2
+
+      decipher = OpenSSL::Cipher.new("aes-128-gcm").decrypt
+      decipher.auth_tag = tag1
+      decipher.key = "x" * 16
+      decipher.iv_len = 12
+      decipher.iv = "a" * 12
+      assert_equal(pt, decipher.update(ct1) << decipher.final)
+
+      decipher.reset
+      decipher.auth_tag = tag2
+      assert_raise(OpenSSL::Cipher::CipherError) {
+        decipher.update(ct2) << decipher.final
+      }
+
+      decipher.reset
+      decipher.auth_tag = tag2
+      decipher.iv_len = 10
+      decipher.iv = "a" * 10
+      assert_equal(pt, decipher.update(ct2) << decipher.final)
+    end
+
   end
 
   private