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require 'concurrent'
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. 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)
@cache_keys["#{salt}#{key_size}"] ||= @key_generator.generate_key(salt, key_size)
end
end
class LegacyKeyGenerator # :nodoc:
SECRET_MIN_LENGTH = 30 # Characters
def initialize(secret)
ensure_secret_secure(secret)
@secret = secret
end
def generate_key(salt)
@secret
end
private
# To prevent users from using something insecure like "Password" we make sure that the
# secret they've provided is at least 30 characters in length.
def ensure_secret_secure(secret)
if secret.blank?
raise ArgumentError, "A secret is required to generate an integrity hash " \
"for cookie session data. Set a secret_key_base of at least " \
"#{SECRET_MIN_LENGTH} characters in config/secrets.yml."
end
if secret.length < SECRET_MIN_LENGTH
raise ArgumentError, "Secret should be something secure, " \
"like \"#{SecureRandom.hex(16)}\". The value you " \
"provided, \"#{secret}\", is shorter than the minimum length " \
"of #{SECRET_MIN_LENGTH} characters."
end
end
end
end
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