use secure string comparisons for basic auth username / password

this will avoid timing attacks against applications that use basic auth.

Conflicts:
	activesupport/lib/active_support/security_utils.rb

Conflicts:
	actionpack/lib/action_controller/metal/http_authentication.rb

CVE-2015-7576

1 files changed, 27 insertions, 0 deletions

diff --git a/activesupport/lib/active_support/security_utils.rb b/activesupport/lib/active_support/security_utils.rb
new file mode 100644
index 0000000000..9be8613ada
--- /dev/null
+++ b/activesupport/lib/active_support/security_utils.rb
@@ -0,0 +1,27 @@
+require 'digest'
+
+module ActiveSupport
+  module SecurityUtils
+    # Constant time string comparison.
+    #
+    # The values compared should be of fixed length, such as strings
+    # that have already been processed by HMAC. This should not be used
+    # on variable length plaintext strings because it could leak length info
+    # via timing attacks.
+    def secure_compare(a, b)
+      return false unless a.bytesize == b.bytesize
+
+      l = a.unpack "C#{a.bytesize}"
+
+      res = 0
+      b.each_byte { |byte| res |= byte ^ l.shift }
+      res == 0
+    end
+    module_function :secure_compare
+
+    def variable_size_secure_compare(a, b) # :nodoc:
+      secure_compare(::Digest::SHA256.hexdigest(a), ::Digest::SHA256.hexdigest(b))
+    end
+    module_function :variable_size_secure_compare
+  end
+end