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Merge pull request #17369 from rails/secure_compare

Secure compare
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guilleiguaran committed Oct 24, 2014
2 parents be49ec4 + 0073d27 commit 1d9ebec0a9e84aa680313b17ceb800f1b10df3b9
@@ -1,5 +1,6 @@
require 'rack/session/abstract/id'
require 'action_controller/metal/exceptions'
require 'active_support/security_utils'
module ActionController #:nodoc:
class InvalidAuthenticityToken < ActionControllerError #:nodoc:
@@ -305,8 +306,7 @@ def valid_authenticity_token?(session, encoded_masked_token)
end
def compare_with_real_token(token, session)
# Borrow a constant-time comparison from Rack
Rack::Utils.secure_compare(token, real_csrf_token(session))
ActiveSupport::SecurityUtils.secure_compare(token, real_csrf_token(session))
end
def real_csrf_token(session)
@@ -1,5 +1,6 @@
require 'base64'
require 'active_support/core_ext/object/blank'
require 'active_support/security_utils'
module ActiveSupport
# +MessageVerifier+ makes it easy to generate and verify messages which are
@@ -37,7 +38,7 @@ def verify(signed_message)
raise InvalidSignature if signed_message.blank?
data, digest = signed_message.split("--")
if data.present? && digest.present? && secure_compare(digest, generate_digest(data))
if data.present? && digest.present? && ActiveSupport::SecurityUtils.secure_compare(digest, generate_digest(data))
begin
@serializer.load(::Base64.strict_decode64(data))
rescue ArgumentError => argument_error
@@ -55,17 +56,6 @@ def generate(value)
end
private
# constant-time comparison algorithm to prevent 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
def generate_digest(data)
require 'openssl' unless defined?(OpenSSL)
OpenSSL::HMAC.hexdigest(OpenSSL::Digest.const_get(@digest).new, @secret, data)
@@ -0,0 +1,20 @@
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
end
end
@@ -0,0 +1,9 @@
require 'abstract_unit'
require 'active_support/security_utils'
class SecurityUtilsTest < ActiveSupport::TestCase
def test_secure_compare_should_perform_string_comparison
assert ActiveSupport::SecurityUtils.secure_compare('a', 'a')
assert !ActiveSupport::SecurityUtils.secure_compare('a', 'b')
end
end

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