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# frozen_string_literal: true
require "base64"
require "active_support/core_ext/object/blank"
require "active_support/security_utils"
require "active_support/messages/metadata"
require "active_support/messages/rotator"
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)
#
# +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 upto the expire time.
# Thereafter, the +verified+ method returns +nil+ while +verify+ raises
# <tt>ActiveSupport::MessageVerifier::InvalidSignature</tt>.
#
# === 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 to
# 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
class MessageVerifier
prepend Messages::Rotator::Verifier
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("--")
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, purpose: nil, **)
if valid_message?(signed_message)
begin
data = signed_message.split("--")[0]
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
def verify(*args)
verified(*args) || 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, 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}--#{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