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.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)
MessageVerifier
creates HMAC signatures using SHA1 hash algorithm by default. If you want to use a different hash algorithm, you can change it by providing :digest
key as an option while initializing the verifier:
@verifier = ActiveSupport::MessageVerifier.new('s3Krit', digest: 'SHA256')
Confining messages to a specific purpose¶ ↑
By default any message can be used throughout your app. But they can also be confined to a specific :purpose
.
token = @verifier.generate("this is the chair", purpose: :login)
Then that same purpose must be passed when verifying to get the data back out:
@verifier.verified(token, purpose: :login) # => "this is the chair" @verifier.verified(token, purpose: :shipping) # => nil @verifier.verified(token) # => nil @verifier.verify(token, purpose: :login) # => "this is the chair" @verifier.verify(token, purpose: :shipping) # => ActiveSupport::MessageVerifier::InvalidSignature @verifier.verify(token) # => ActiveSupport::MessageVerifier::InvalidSignature
Likewise, if a message has no purpose it won't be returned when verifying with a specific purpose.
token = @verifier.generate("the conversation is lively") @verifier.verified(token, purpose: :scare_tactics) # => nil @verifier.verified(token) # => "the conversation is lively" @verifier.verify(token, purpose: :scare_tactics) # => ActiveSupport::MessageVerifier::InvalidSignature @verifier.verify(token) # => "the conversation is lively"
Making messages expire¶ ↑
By default messages last forever and verifying one year from now will still return the original value. But messages can be set to expire at a given time with :expires_in
or :expires_at
.
@verifier.generate("parcel", expires_in: 1.month) @verifier.generate("doowad", expires_at: Time.now.end_of_year)
Then the messages can be verified and returned up to the expire time. Thereafter, the verified
method returns nil
while verify
raises ActiveSupport::MessageVerifier::InvalidSignature
.
Rotating keys¶ ↑
MessageVerifier
also supports rotating out old configurations by falling back to a stack of verifiers. Call rotate
to build and add a verifier so either verified
or verify
will also try verifying with the fallback.
By default any rotated verifiers use the values of the primary verifier unless specified otherwise.
You'd give your verifier the new defaults:
verifier = ActiveSupport::MessageVerifier.new(@secret, digest: "SHA512", serializer: JSON)
Then gradually rotate the old values out by adding them as fallbacks. Any message generated with the old values will then work until the rotation is removed.
verifier.rotate old_secret # Fallback to an old secret instead of @secret. verifier.rotate digest: "SHA256" # Fallback to an old digest instead of SHA512. verifier.rotate serializer: Marshal # Fallback to an old serializer instead of JSON.
Though the above would most likely be combined into one rotation:
verifier.rotate old_secret, digest: "SHA256", serializer: Marshal
Public Class Methods
# File lib/active_support/message_verifier.rb, line 110 def initialize(secret, digest: nil, serializer: nil) raise ArgumentError, "Secret should not be nil." unless secret @secret = secret @digest = digest&.to_s || "SHA1" @serializer = serializer || Marshal end
Public Instance Methods
Generates a signed message for the provided value.
The message is signed with the MessageVerifier
's secret. Returns Base64-encoded message joined with the generated signature.
verifier = ActiveSupport::MessageVerifier.new 's3Krit' verifier.generate 'a private message' # => "BAhJIhRwcml2YXRlLW1lc3NhZ2UGOgZFVA==--e2d724331ebdee96a10fb99b089508d1c72bd772"
# File lib/active_support/message_verifier.rb, line 188 def generate(value, expires_at: nil, expires_in: nil, purpose: nil) data = encode(Messages::Metadata.wrap(@serializer.dump(value), expires_at: expires_at, expires_in: expires_in, purpose: purpose)) "#{data}#{SEPARATOR}#{generate_digest(data)}" 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
# File lib/active_support/message_verifier.rb, line 126 def valid_message?(signed_message) data, digest = get_data_and_digest_from(signed_message) digest_matches_data?(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
# File lib/active_support/message_verifier.rb, line 152 def verified(signed_message, purpose: nil, **) data, digest = get_data_and_digest_from(signed_message) if digest_matches_data?(digest, data) begin message = Messages::Metadata.verify(decode(data), purpose) @serializer.load(message) if message rescue ArgumentError => argument_error return if argument_error.message.include?("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
# File lib/active_support/message_verifier.rb, line 177 def verify(*args, **options) verified(*args, **options) || raise(InvalidSignature) end
Private Instance Methods
# File lib/active_support/message_verifier.rb, line 198 def decode(data) ::Base64.strict_decode64(data) end
# File lib/active_support/message_verifier.rb, line 206 def digest_length_in_hex # In hexadecimal (AKA base16) it takes 4 bits to represent a character, # hence we multiply the digest's length (in bytes) by 8 to get it in # bits and divide by 4 to get its number of characters it hex. Well, 8 # divided by 4 is 2. @digest_length_in_hex ||= OpenSSL::Digest.new(@digest).digest_length * 2 end
# File lib/active_support/message_verifier.rb, line 233 def digest_matches_data?(digest, data) data.present? && digest.present? && ActiveSupport::SecurityUtils.secure_compare(digest, generate_digest(data)) end
# File lib/active_support/message_verifier.rb, line 194 def encode(data) ::Base64.strict_encode64(data) end
# File lib/active_support/message_verifier.rb, line 202 def generate_digest(data) OpenSSL::HMAC.hexdigest(@digest, @secret, data) end
# File lib/active_support/message_verifier.rb, line 221 def get_data_and_digest_from(signed_message) return if signed_message.nil? || !signed_message.valid_encoding? || signed_message.empty? separator_index = separator_index_for(signed_message) return if separator_index.nil? data = signed_message[0...separator_index] digest = signed_message[separator_index + SEPARATOR_LENGTH..-1] [data, digest] end
# File lib/active_support/message_verifier.rb, line 214 def separator_index_for(signed_message) index = signed_message.length - digest_length_in_hex - SEPARATOR_LENGTH return if index.negative? || signed_message[index, SEPARATOR_LENGTH] != SEPARATOR index end