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 # signed to prevent tampering. # # This is useful for cases like remember-me tokens and auto-unsubscribe links # where the session store isn't suitable or available. # # Remember Me: # cookies[:remember_me] = @verifier.generate([@user.id, 2.weeks.from_now]) # # In the authentication filter: # # id, time = @verifier.verify(cookies[:remember_me]) # if Time.now < time # self.current_user = User.find(id) # end # # By default it uses Marshal to serialize the message. If you want to use # another serialization method, you can set the serializer in the options # hash upon initialization: # # @verifier = ActiveSupport::MessageVerifier.new('s3Krit', serializer: YAML) class MessageVerifier class InvalidSignature < StandardError; end def initialize(secret, options = {}) raise ArgumentError, 'Secret should not be nil.' unless secret @secret = secret @digest = options[:digest] || 'SHA1' @serializer = options[:serializer] || Marshal end # Checks if a signed message could have been generated by signing an object # with the +MessageVerifier+'s secret. # # verifier = ActiveSupport::MessageVerifier.new 's3Krit' # signed_message = verifier.generate 'a private message' # verifier.valid_message?(signed_message) # => true # # tampered_message = signed_message.chop # editing the message invalidates the signature # verifier.valid_message?(tampered_message) # => false def valid_message?(signed_message) return if signed_message.nil? || !signed_message.valid_encoding? || signed_message.blank? data, digest = signed_message.split("--".freeze) data.present? && digest.present? && ActiveSupport::SecurityUtils.secure_compare(digest, generate_digest(data)) end # Decodes the signed message using the +MessageVerifier+'s secret. # # verifier = ActiveSupport::MessageVerifier.new 's3Krit' # # signed_message = verifier.generate 'a private message' # verifier.verified(signed_message) # => 'a private message' # # Returns +nil+ if the message was not signed with the same secret. # # other_verifier = ActiveSupport::MessageVerifier.new 'd1ff3r3nt-s3Krit' # other_verifier.verified(signed_message) # => nil # # Returns +nil+ if the message is not Base64-encoded. # # invalid_message = "f--46a0120593880c733a53b6dad75b42ddc1c8996d" # verifier.verified(invalid_message) # => nil # # Raises any error raised while decoding the signed message. # # incompatible_message = "test--dad7b06c94abba8d46a15fafaef56c327665d5ff" # verifier.verified(incompatible_message) # => TypeError: incompatible marshal file format def verified(signed_message) if valid_message?(signed_message) begin data = signed_message.split("--".freeze)[0] @serializer.load(decode(data)) rescue ArgumentError => argument_error return if argument_error.message =~ %r{invalid base64} raise end end end # Decodes the signed message using the +MessageVerifier+'s secret. # # verifier = ActiveSupport::MessageVerifier.new 's3Krit' # signed_message = verifier.generate 'a private message' # # verifier.verify(signed_message) # => 'a private message' # # Raises +InvalidSignature+ if the message was not signed with the same # secret or was not Base64-encoded. # # other_verifier = ActiveSupport::MessageVerifier.new 'd1ff3r3nt-s3Krit' # other_verifier.verify(signed_message) # => ActiveSupport::MessageVerifier::InvalidSignature def verify(signed_message) verified(signed_message) || raise(InvalidSignature) end # Generates a signed message for the provided value. # # The message is signed with the +MessageVerifier+'s secret. Without knowing # the secret, the original value cannot be extracted from the message. # # verifier = ActiveSupport::MessageVerifier.new 's3Krit' # verifier.generate 'a private message' # => "BAhJIhRwcml2YXRlLW1lc3NhZ2UGOgZFVA==--e2d724331ebdee96a10fb99b089508d1c72bd772" def generate(value) data = encode(@serializer.dump(value)) "#{data}--#{generate_digest(data)}" end private def encode(data) ::Base64.strict_encode64(data) end def decode(data) ::Base64.strict_decode64(data) end def generate_digest(data) require 'openssl' unless defined?(OpenSSL) OpenSSL::HMAC.hexdigest(OpenSSL::Digest.const_get(@digest).new, @secret, data) end end end