class ActiveSupport::MessageVerifier
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 < Time.now 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 attribute to something that responds to dump and load, e.g.:
@verifier.serializer = YAML
Public Class Methods
new(secret, options = {})
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# File lib/active_support/message_verifier.rb, line 30 def initialize(secret, options = {}) unless options.is_a?(Hash) ActiveSupport::Deprecation.warn "The second parameter should be an options hash. Use :digest => 'algorithm' to specify the digest algorithm." options = { :digest => options } end @secret = secret @digest = options[:digest] || 'SHA1' @serializer = options[:serializer] || Marshal end
Public Instance Methods
generate(value)
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# File lib/active_support/message_verifier.rb, line 52 def generate(value) data = ::Base64.strict_encode64(@serializer.dump(value)) "#{data}--#{generate_digest(data)}" end
verify(signed_message)
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# File lib/active_support/message_verifier.rb, line 41 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)) @serializer.load(::Base64.decode64(data)) else raise InvalidSignature end end
Private Instance Methods
generate_digest(data)
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# File lib/active_support/message_verifier.rb, line 69 def generate_digest(data) require 'openssl' unless defined?(OpenSSL) OpenSSL::HMAC.hexdigest(OpenSSL::Digest.const_get(@digest).new, @secret, data) end
secure_compare(a, b)
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constant-time comparison algorithm to prevent timing attacks
# File lib/active_support/message_verifier.rb, line 59 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