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require 'base64'
require 'active_support/core_ext/object/blank'
require 'active_support/security_utils'
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')
class MessageVerifier
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("--".freeze)
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)
if valid_message?(signed_message)
begin
data = signed_message.split("--".freeze)[0]
@serializer.load(decode(data))
rescue ArgumentError => argument_error
return if argument_error.message =~ %r{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(signed_message)
verified(signed_message) || 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)
data = encode(@serializer.dump(value))
"#{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
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