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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 in the options hash upon initialization:

@verifier = ActiveSupport::MessageVerifier.new('s3Krit', serializer: YAML)
Namespace
Methods
G
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Class Public methods
new(secret, options = {})
# File activesupport/lib/active_support/message_verifier.rb, line 30
def initialize(secret, options = {})
  raise ArgumentError, 'Secret should not be nil.' unless secret
  @secret = secret
  @digest = options[:digest] || 'SHA1'
  @serializer = options[:serializer] || Marshal
end
Instance Public methods
generate(value)

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"
# File activesupport/lib/active_support/message_verifier.rb, line 109
def generate(value)
  data = encode(@serializer.dump(value))
  "#{data}--#{generate_digest(data)}"
end
valid_message?(signed_message)

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
# File activesupport/lib/active_support/message_verifier.rb, line 46
def valid_message?(signed_message)
  return if signed_message.blank?

  data, digest = signed_message.split("--")
  data.present? && digest.present? && ActiveSupport::SecurityUtils.secure_compare(digest, generate_digest(data))
end
verified(signed_message)

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
# File activesupport/lib/active_support/message_verifier.rb, line 74
def verified(signed_message)
  if valid_message?(signed_message)
    begin
      data = signed_message.split("--")[0]
      @serializer.load(decode(data))
    rescue ArgumentError => argument_error
      return if argument_error.message =~ %r{invalid base64}
      raise
    end
  end
end
verify(signed_message)

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
# File activesupport/lib/active_support/message_verifier.rb, line 98
def verify(signed_message)
  verified(signed_message) || raise(InvalidSignature)
end