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# frozen_string_literal: true
require "concurrent/map"
require "openssl"
module ActiveSupport
# KeyGenerator is a simple wrapper around OpenSSL's implementation of PBKDF2.
# It can be used to derive a number of keys for various purposes from a given secret.
# This lets Rails applications have a single secure secret, but avoid reusing that
# key in multiple incompatible contexts.
class KeyGenerator
def initialize(secret, options = {})
@secret = secret
# The default iterations are higher than required for our key derivation uses
# on the off chance someone uses this for password storage
@iterations = options[:iterations] || 2**16
end
# Returns a derived key suitable for use. The default key_size is chosen
# to be compatible with the default settings of ActiveSupport::MessageVerifier.
# i.e. OpenSSL::Digest::SHA1#block_length
def generate_key(salt, key_size = 64)
OpenSSL::PKCS5.pbkdf2_hmac_sha1(@secret, salt, @iterations, key_size)
end
end
# CachingKeyGenerator is a wrapper around KeyGenerator which allows users to avoid
# re-executing the key generation process when it's called using the same salt and
# key_size.
class CachingKeyGenerator
def initialize(key_generator)
@key_generator = key_generator
@cache_keys = Concurrent::Map.new
end
# Returns a derived key suitable for use.
def generate_key(*args)
@cache_keys[args.join] ||= @key_generator.generate_key(*args)
end
end
end
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