From 326608baafb57dc32b1ffd4499a40e1cf473e3aa Mon Sep 17 00:00:00 2001
From: arrtchiu <arrtchiu@gmail.com>
Date: Tue, 29 Jul 2014 18:23:40 +0800
Subject: [PATCH] add timing safe string compare method

---
 configure.in             |  2 ++
 string.c                 | 52 ++++++++++++++++++++++++++++++++++++++++++++++++
 test/ruby/test_string.rb |  7 +++++++
 3 files changed, 61 insertions(+)

diff --git a/configure.in b/configure.in
index 2cbe36f..8560d82 100644
--- a/configure.in
+++ b/configure.in
@@ -2066,6 +2066,8 @@ AC_CHECK_FUNCS(utimensat)
 AC_CHECK_FUNCS(utimes)
 AC_CHECK_FUNCS(wait4)
 AC_CHECK_FUNCS(waitpid)
+AC_CHECK_FUNCS(consttime_memequal)
+AC_CHECK_FUNCS(timingsafe_memcmp)
 
 AS_IF([test "$ac_cv_func_getcwd" = yes], [
     AC_CACHE_CHECK(if getcwd allocates buffer if NULL is given, [rb_cv_getcwd_malloc],
diff --git a/string.c b/string.c
index 9f06837..e8ed3cf 100644
--- a/string.c
+++ b/string.c
@@ -2490,6 +2490,57 @@ rb_str_eql(VALUE str1, VALUE str2)
     return str_eql(str1, str2);
 }
 
+static inline VALUE
+rb_tsafe_eql(const char* buf1, const char* buf2, long len)
+{
+#if defined(HAVE_TIMINGSAFE_MEMCMP)
+    return (timingsafe_memcmp(buf1, buf2, len) == 0);
+#elif defined(HAVE_CONSTTIME_MEMEQUAL)
+    return (consttime_memequal(buf1, buf2, len) != 0);
+#else
+    VALUE result;
+    long idx;
+
+    result = 0;
+    idx = 0;
+    if (UNALIGNED_WORD_ACCESS || !((VALUE)buf1 % sizeof(VALUE)) && !((VALUE)buf2 % sizeof(VALUE))) {
+        for (; idx < len; idx += sizeof(VALUE)) {
+            result |= *(const VALUE *)(buf1+idx) ^ *(const VALUE *)(buf2+idx);
+        }
+    }
+
+    for (; idx < len; idx++) {
+        result |= buf1[idx] ^ buf2[idx];
+    }
+
+    return (result == 0);
+#endif
+}
+
+/*
+ * call-seq:
+ *   str.tsafe_eql?(other)   -> true or false
+ *
+ * Compares each byte of +str+ against +other+, similarly to String#eql?, but
+ * performs the comparison in constant-time.
+ *
+ * This method is timing-safe if both strings are of equal length.
+ */
+
+static VALUE
+rb_str_tsafe_eql(VALUE str1, VALUE str2)
+{
+    long len;
+
+    str2 = StringValue(str2);
+    len = RSTRING_LEN(str1);
+
+    if (RSTRING_LEN(str2) != len) return Qfalse;
+    if (rb_tsafe_eql(RSTRING_PTR(str1), RSTRING_PTR(str2), len) != 0) return Qtrue;
+
+    return Qfalse;
+}
+
 /*
  *  call-seq:
  *     string <=> other_string   -> -1, 0, +1 or nil
@@ -8761,6 +8812,7 @@ Init_String(void)
     rb_define_method(rb_cString, "==", rb_str_equal, 1);
     rb_define_method(rb_cString, "===", rb_str_equal, 1);
     rb_define_method(rb_cString, "eql?", rb_str_eql, 1);
+    rb_define_method(rb_cString, "tsafe_eql?", rb_str_tsafe_eql, 1);
     rb_define_method(rb_cString, "hash", rb_str_hash_m, 0);
     rb_define_method(rb_cString, "casecmp", rb_str_casecmp, 1);
     rb_define_method(rb_cString, "+", rb_str_plus, 1);
diff --git a/test/ruby/test_string.rb b/test/ruby/test_string.rb
index e8decc0..384230d 100644
--- a/test/ruby/test_string.rb
+++ b/test/ruby/test_string.rb
@@ -304,6 +304,13 @@ class TestString < Test::Unit::TestCase
     casetest(S("CaT"), S('cAt'), true) # find these in the case.
   end
 
+  def test_TIMING_SAFE_EQUAL # 'tsafe_eql?'
+    assert_equal(true, S("foo").tsafe_eql?(S("foo")))
+    assert_equal(false, S("foo").tsafe_eql?(S("foO")))
+    assert_equal(true, S("f\x00oo").tsafe_eql?(S("f\x00oo")))
+    assert_equal(false, S("f\x00oo").tsafe_eql?(S("f\x00oO")))
+  end
+
   def test_capitalize
     assert_equal(S("Hello"),  S("hello").capitalize)
     assert_equal(S("Hello"),  S("hELLO").capitalize)
-- 
1.8.5.2 (Apple Git-48)