From 4be74741d5b130014dcb6d6387ce91e685637122 Mon Sep 17 00:00:00 2001
From: Didactic Drunk <1479616+didactic-drunk@users.noreply.github.com>
Date: Mon, 5 Aug 2019 18:49:17 -0700
Subject: [PATCH] Use timing safe compare in Sodium::SecureBuffer.

---
 src/sodium/error.cr         |  3 +++
 src/sodium/lib_sodium.cr    | 23 +++++++++++++++++++++++
 src/sodium/secure_buffer.cr |  4 ++--
 src/sodium/wipe.cr          |  6 ------
 4 files changed, 28 insertions(+), 8 deletions(-)

diff --git a/src/sodium/error.cr b/src/sodium/error.cr
index 68c5cff..9cc7aff 100644
--- a/src/sodium/error.cr
+++ b/src/sodium/error.cr
@@ -7,5 +7,8 @@ module Sodium
 
     class DecryptionFailed < Error
     end
+
+    class MemcmpFailed < Error
+    end
   end
 end
diff --git a/src/sodium/lib_sodium.cr b/src/sodium/lib_sodium.cr
index 23cb917..daf6a80 100644
--- a/src/sodium/lib_sodium.cr
+++ b/src/sodium/lib_sodium.cr
@@ -45,6 +45,7 @@ module Sodium
     fun crypto_generichash_blake2b_saltbytes : LibC::SizeT
     fun crypto_generichash_blake2b_personalbytes : LibC::SizeT
 
+    fun sodium_memcmp(Pointer(LibC::UChar), Pointer(LibC::UChar), LibC::SizeT) : LibC::Int
     fun sodium_memzero(Pointer(LibC::UChar), LibC::SizeT) : Nil
 
     fun sodium_malloc(LibC::SizeT) : Pointer(LibC::UChar)
@@ -280,3 +281,25 @@ module Sodium
     raise "Assumptions in this library regarding nonce sizes may not be valid"
   end
 end
+
+module Sodium
+  def self.memcmp(a : Bytes, b : Bytes) : Bool
+    if a.bytesize != b.bytesize
+      false
+    elsif LibSodium.sodium_memcmp(a, b, a.bytesize) == 0
+      true
+    else
+      false
+    end
+  end
+
+  # Raises unless comparison succeeds.
+  def self.memcmp!(a, b)
+    raise Error::MemcmpFailed.new unless memcmp(a, b)
+    true
+  end
+
+  def self.memzero(bytes : Bytes)
+    LibSodium.sodium_memzero bytes, bytes.bytesize
+  end
+end
diff --git a/src/sodium/secure_buffer.cr b/src/sodium/secure_buffer.cr
index dbc1fa4..657fc49 100644
--- a/src/sodium/secure_buffer.cr
+++ b/src/sodium/secure_buffer.cr
@@ -82,11 +82,11 @@ module Sodium
     end
 
     def ==(other : self)
-      self.to_slice == other.to_slice
+      Sodium.memcmp self.to_slice, other.to_slice
     end
 
     def ==(other : Bytes)
-      self.to_slice == other
+      Sodium.memcmp self.to_slice, other
     end
   end
 end
diff --git a/src/sodium/wipe.cr b/src/sodium/wipe.cr
index 2985cc0..798a90b 100644
--- a/src/sodium/wipe.cr
+++ b/src/sodium/wipe.cr
@@ -1,9 +1,3 @@
-module Sodium
-  def self.memzero(bytes : Bytes)
-    LibSodium.sodium_memzero bytes, bytes.bytesize
-  end
-end
-
 module Sodium::Wipe
   annotation Var
   end