Active Support Message Verifier
MessageVerifier
makes it easy to generate and verify messages which are signed to prevent tampering.
In a Rails application, you can use Rails.application.message_verifier
to manage unique instances of verifiers for each use case. Learn more.
This is useful for cases like remember-me tokens and auto-unsubscribe links where the session store isn’t suitable or available.
First, generate a signed message:
cookies[:remember_me] = Rails.application.message_verifier(:remember_me).generate([@user.id, 2.weeks.from_now])
Later verify that message:
id, time = Rails.application.message_verifier(:remember_me).verify(cookies[:remember_me])
if time.future?
self.current_user = User.find(id)
end
Signing is not encryption
The signed messages are not encrypted. The payload is merely encoded (Base64 by default) and can be decoded by anyone. The signature is just assuring that the message wasn’t tampered with. For example:
message = Rails.application.message_verifier('my_purpose').generate('never put secrets here')
# => "BAhJIhtuZXZlciBwdXQgc2VjcmV0cyBoZXJlBjoGRVQ=--a0c1c0827919da5e949e989c971249355735e140"
Base64.decode64(message.split("--").first) # no key needed
# => 'never put secrets here'
If you also need to encrypt the contents, you must use ActiveSupport::MessageEncryptor
instead.
Confine messages to a specific purpose
It’s not recommended to use the same verifier for different purposes in your application. Doing so could allow a malicious actor to re-use a signed message to perform an unauthorized action. You can reduce this risk by confining signed messages to a specific :purpose
.
token = @verifier.generate("signed message", purpose: :login)
Then that same purpose must be passed when verifying to get the data back out:
@verifier.verified(token, purpose: :login) # => "signed message"
@verifier.verified(token, purpose: :shipping) # => nil
@verifier.verified(token) # => nil
@verifier.verify(token, purpose: :login) # => "signed message"
@verifier.verify(token, purpose: :shipping) # => raises ActiveSupport::MessageVerifier::InvalidSignature
@verifier.verify(token) # => raises ActiveSupport::MessageVerifier::InvalidSignature
Likewise, if a message has no purpose it won’t be returned when verifying with a specific purpose.
token = @verifier.generate("signed message")
@verifier.verified(token, purpose: :redirect) # => nil
@verifier.verified(token) # => "signed message"
@verifier.verify(token, purpose: :redirect) # => raises ActiveSupport::MessageVerifier::InvalidSignature
@verifier.verify(token) # => "signed message"
Expiring messages
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("signed message", expires_in: 1.month)
@verifier.generate("signed message", expires_at: Time.now.end_of_year)
Messages
can then be verified and returned until expiry. 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)
- G
- N
- V
Class Public methods
new(secret, **options) Link
Initialize a new MessageVerifier
with a secret for the signature.
Options
:digest
-
Digest
used for signing. The default is"SHA1"
. SeeOpenSSL::Digest
for alternatives. :serializer
-
The serializer used to serialize message data. You can specify any object that responds to
dump
andload
, or you can choose from several preconfigured serializers::marshal
,:json_allow_marshal
,:json
,:message_pack_allow_marshal
,:message_pack
.The preconfigured serializers include a fallback mechanism to support multiple deserialization formats. For example, the
:marshal
serializer will serialize usingMarshal
, but can deserialize usingMarshal
,ActiveSupport::JSON
, orActiveSupport::MessagePack
. This makes it easy to migrate between serializers.The
:marshal
,:json_allow_marshal
, and:message_pack_allow_marshal
serializers support deserializing usingMarshal
, but the others do not. Beware thatMarshal
is a potential vector for deserialization attacks in cases where a message signing secret has been leaked. If possible, choose a serializer that does not supportMarshal
.The
:message_pack
and:message_pack_allow_marshal
serializers useActiveSupport::MessagePack
, which can roundtrip some Ruby types that are not supported byJSON
, and may provide improved performance. However, these require themsgpack
gem.When using Rails, the default depends on
config.active_support.message_serializer
. Otherwise, the default is:marshal
. :url_safe
-
By default,
MessageVerifier
generates RFC 4648 compliant strings which are not URL-safe. In other words, they can contain “+” and “/”. If you want to generate URL-safe strings (in compliance with “Base 64 Encoding with URL and Filename Safe Alphabet” in RFC 4648), you can passtrue
. :force_legacy_metadata_serializer
-
Whether to use the legacy metadata serializer, which serializes the message first, then wraps it in an envelope which is also serialized. This was the default in Rails 7.0 and below.
If you don’t pass a truthy value, the default is set using
config.active_support.use_message_serializer_for_metadata
.
Instance Public methods
generate(value, **options) Link
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("secret")
verifier.generate("signed message") # => "BAhJIhNzaWduZWQgbWVzc2FnZQY6BkVU--f67d5f27c3ee0b8483cebf2103757455e947493b"
Options
:expires_at
-
The datetime at which the message expires. After this datetime, verification of the message will fail.
message = verifier.generate("hello", expires_at: Time.now.tomorrow) verifier.verified(message) # => "hello" # 24 hours later... verifier.verified(message) # => nil verifier.verify(message) # => raises ActiveSupport::MessageVerifier::InvalidSignature
:expires_in
-
The duration for which the message is valid. After this duration has elapsed, verification of the message will fail.
message = verifier.generate("hello", expires_in: 24.hours) verifier.verified(message) # => "hello" # 24 hours later... verifier.verified(message) # => nil verifier.verify(message) # => raises ActiveSupport::MessageVerifier::InvalidSignature
:purpose
-
The purpose of the message. If specified, the same purpose must be specified when verifying the message; otherwise, verification will fail. (See
verified
andverify
.)
valid_message?(message) Link
Checks if a signed message could have been generated by signing an object with the MessageVerifier
‘s secret.
verifier = ActiveSupport::MessageVerifier.new("secret")
signed_message = verifier.generate("signed message")
verifier.valid_message?(signed_message) # => true
tampered_message = signed_message.chop # editing the message invalidates the signature
verifier.valid_message?(tampered_message) # => false
verified(message, **options) Link
Decodes the signed message using the MessageVerifier
‘s secret.
verifier = ActiveSupport::MessageVerifier.new("secret")
signed_message = verifier.generate("signed message")
verifier.verified(signed_message) # => "signed message"
Returns nil
if the message was not signed with the same secret.
other_verifier = ActiveSupport::MessageVerifier.new("different_secret")
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
Options
:purpose
-
The purpose that the message was generated with. If the purpose does not match,
verified
will returnnil
.message = verifier.generate("hello", purpose: "greeting") verifier.verified(message, purpose: "greeting") # => "hello" verifier.verified(message, purpose: "chatting") # => nil verifier.verified(message) # => nil message = verifier.generate("bye") verifier.verified(message) # => "bye" verifier.verified(message, purpose: "greeting") # => nil
# File activesupport/lib/active_support/message_verifier.rb, line 222 def verified(message, **options) catch_and_ignore :invalid_message_format do catch_and_raise :invalid_message_serialization do catch_and_ignore :invalid_message_content do read_message(message, **options) end end end end
verify(message, **options) Link
Decodes the signed message using the MessageVerifier
‘s secret.
verifier = ActiveSupport::MessageVerifier.new("secret")
signed_message = verifier.generate("signed message")
verifier.verify(signed_message) # => "signed message"
Raises InvalidSignature
if the message was not signed with the same secret or was not Base64-encoded.
other_verifier = ActiveSupport::MessageVerifier.new("different_secret")
other_verifier.verify(signed_message) # => ActiveSupport::MessageVerifier::InvalidSignature
Options
:purpose
-
The purpose that the message was generated with. If the purpose does not match,
verify
will raiseActiveSupport::MessageVerifier::InvalidSignature
.message = verifier.generate("hello", purpose: "greeting") verifier.verify(message, purpose: "greeting") # => "hello" verifier.verify(message, purpose: "chatting") # => raises InvalidSignature verifier.verify(message) # => raises InvalidSignature message = verifier.generate("bye") verifier.verify(message) # => "bye" verifier.verify(message, purpose: "greeting") # => raises InvalidSignature
# File activesupport/lib/active_support/message_verifier.rb, line 260 def verify(message, **options) catch_and_raise :invalid_message_format, as: InvalidSignature do catch_and_raise :invalid_message_serialization do catch_and_raise :invalid_message_content, as: InvalidSignature do read_message(message, **options) end end end end