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# frozen_string_literal: true
module JWT
module JWA
# Implementation of the HMAC family of algorithms
class Hmac
include JWT::JWA::SigningAlgorithm
def initialize(alg, digest)
@alg = alg
@digest = digest
end
def sign(data:, signing_key:)
signing_key ||= ''
raise_verify_error!('HMAC key expected to be a String') unless signing_key.is_a?(String)
OpenSSL::HMAC.digest(digest.new, signing_key, data)
rescue OpenSSL::HMACError => e
raise_verify_error!('OpenSSL 3.0 does not support nil or empty hmac_secret') if signing_key == '' && e.message == 'EVP_PKEY_new_mac_key: malloc failure'
raise e
end
def verify(data:, signature:, verification_key:)
SecurityUtils.secure_compare(signature, sign(data: data, signing_key: verification_key))
end
register_algorithm(new('HS256', OpenSSL::Digest::SHA256))
register_algorithm(new('HS384', OpenSSL::Digest::SHA384))
register_algorithm(new('HS512', OpenSSL::Digest::SHA512))
private
attr_reader :digest
# Copy of https://github.com/rails/rails/blob/v7.0.3.1/activesupport/lib/active_support/security_utils.rb
# rubocop:disable Naming/MethodParameterName, Style/StringLiterals, Style/NumericPredicate
module SecurityUtils
# Constant time string comparison, for fixed length strings.
#
# The values compared should be of fixed length, such as strings
# that have already been processed by HMAC. Raises in case of length mismatch.
if defined?(OpenSSL.fixed_length_secure_compare)
def fixed_length_secure_compare(a, b)
OpenSSL.fixed_length_secure_compare(a, b)
end
else
# :nocov:
def fixed_length_secure_compare(a, b)
raise ArgumentError, "string length mismatch." unless a.bytesize == b.bytesize
l = a.unpack "C#{a.bytesize}"
res = 0
b.each_byte { |byte| res |= byte ^ l.shift }
res == 0
end
# :nocov:
end
module_function :fixed_length_secure_compare
# Secure string comparison for strings of variable length.
#
# While a timing attack would not be able to discern the content of
# a secret compared via secure_compare, it is possible to determine
# the secret length. This should be considered when using secure_compare
# to compare weak, short secrets to user input.
def secure_compare(a, b)
a.bytesize == b.bytesize && fixed_length_secure_compare(a, b)
end
module_function :secure_compare
end
# rubocop:enable Naming/MethodParameterName, Style/StringLiterals, Style/NumericPredicate
end
end
end
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