From 46c571c9a994603c4ff538b7c307592bd830ee0c Mon Sep 17 00:00:00 2001
From: arrtchiu <arrtchiu@gmail.com>
Date: Mon, 28 Jul 2014 18:18:33 +0800
Subject: [PATCH] add timing-safe hmac verify method

---
 ext/openssl/ossl_hmac.c   | 41 +++++++++++++++++++++++++++++++++++++++++
 test/openssl/test_hmac.rb |  6 ++++++
 2 files changed, 47 insertions(+)

diff --git a/ext/openssl/ossl_hmac.c b/ext/openssl/ossl_hmac.c
index b1e853d..27c2fed 100644
--- a/ext/openssl/ossl_hmac.c
+++ b/ext/openssl/ossl_hmac.c
@@ -324,6 +324,46 @@ ossl_hmac_s_hexdigest(VALUE klass, VALUE digest, VALUE key, VALUE data)
 }
 
 /*
+ *  call-seq:
+ *     hmac.verify(bytes) -> aBoolean
+ *
+ * Compares the receiver's digest to another digest in a timing-safe way.
+ * +bytes+ must be a binary string containing a digest, for example by calling +#digest+ on another
+ * instance of +OpenSSL::Digest+.
+ */
+VALUE
+ossl_hmac_verify(VALUE self, VALUE other)
+{
+  HMAC_CTX *ctx;
+  unsigned char *buf;
+  unsigned int buf_len;
+  unsigned char result;
+  unsigned int cur_idx;
+  unsigned char *other_buf;
+
+  if (!RB_TYPE_P(other, T_STRING))
+    rb_raise(rb_eArgError, "Must supply binary string or instance of OpenSSL::HMAC");
+
+  GetHMAC(self, ctx);
+  hmac_final(ctx, &buf, &buf_len);
+
+  if (!buf_len || buf_len != RSTRING_LEN(other))
+    return Qfalse;
+
+  other_buf = (unsigned char *)RSTRING_PTR(other);
+
+  result = 0;
+  for (cur_idx = 0; cur_idx < buf_len; cur_idx++) {
+    result |= buf[cur_idx] ^ other_buf[cur_idx];
+  }
+
+  if (result == 0)
+    return Qtrue;
+
+  return Qfalse;
+}
+
+/*
  * INIT
  */
 void
@@ -352,6 +392,7 @@ Init_ossl_hmac()
     rb_define_method(cHMAC, "hexdigest", ossl_hmac_hexdigest, 0);
     rb_define_alias(cHMAC, "inspect", "hexdigest");
     rb_define_alias(cHMAC, "to_s", "hexdigest");
+    rb_define_method(cHMAC, "verify", ossl_hmac_verify, 1);
 }
 
 #else /* NO_HMAC */
diff --git a/test/openssl/test_hmac.rb b/test/openssl/test_hmac.rb
index f1e4536..bd2e9d3 100644
--- a/test/openssl/test_hmac.rb
+++ b/test/openssl/test_hmac.rb
@@ -24,6 +24,12 @@ class OpenSSL::TestHMAC < Test::Unit::TestCase
 
     assert_equal(OpenSSL::HMAC.digest("MD5", @key, @data), @h2.digest, "digest")
     assert_equal(OpenSSL::HMAC.hexdigest("MD5", @key, @data), @h2.hexdigest, "hexdigest")
+
+    assert_same(false, @h1.verify("\x9EPYl\x0F\xA1\x19\x7F\x85\x87D:\x94-\x8A\xFD"))
+    assert_same(true, @h1.verify("\x9EPYl\x0F\xA1\x19\x7F\x85\x87D:\x94-\x8A\xFC"))
+  end
+
+  def test_hmac_verify
   end
 
   def test_dup
-- 
1.8.5.2 (Apple Git-48)