module Rails # A class for creating random secret keys. This class will do its best to create a # random secret key that's as secure as possible, using whatever methods are # available on the current platform. For example: # # generator = Rails::SecretKeyGenerator("some unique identifier, such as the application name") # generator.generate_secret # => "f3f1be90053fa851... (some long string)" class SecretKeyGenerator GENERATORS = [ :secure_random, :win32_api, :urandom, :openssl, :prng ].freeze def initialize(identifier) @identifier = identifier end # Generate a random secret key with the best possible method available on # the current platform. def generate_secret generator = GENERATORS.find do |g| self.class.send("supports_#{g}?") end send("generate_secret_with_#{generator}") end # Generate a random secret key by using the Win32 API. Raises LoadError # if the current platform cannot make use of the Win32 API. Raises # SystemCallError if some other error occured. def generate_secret_with_win32_api # Following code is based on David Garamond's GUID library for Ruby. require 'Win32API' crypt_acquire_context = Win32API.new("advapi32", "CryptAcquireContext", 'PPPII', 'L') crypt_gen_random = Win32API.new("advapi32", "CryptGenRandom", 'LIP', 'L') crypt_release_context = Win32API.new("advapi32", "CryptReleaseContext", 'LI', 'L') prov_rsa_full = 1 crypt_verifycontext = 0xF0000000 hProvStr = " " * 4 if crypt_acquire_context.call(hProvStr, nil, nil, prov_rsa_full, crypt_verifycontext) == 0 raise SystemCallError, "CryptAcquireContext failed: #{lastWin32ErrorMessage}" end hProv, = hProvStr.unpack('L') bytes = " " * 64 if crypt_gen_random.call(hProv, bytes.size, bytes) == 0 raise SystemCallError, "CryptGenRandom failed: #{lastWin32ErrorMessage}" end if crypt_release_context.call(hProv, 0) == 0 raise SystemCallError, "CryptReleaseContext failed: #{lastWin32ErrorMessage}" end bytes.unpack("H*")[0] end # Generate a random secret key with Ruby 1.9's SecureRandom module. # Raises LoadError if the current Ruby version does not support # SecureRandom. def generate_secret_with_secure_random require 'securerandom' return SecureRandom.hex(64) end # Generate a random secret key with OpenSSL. If OpenSSL is not # already loaded, then this method will attempt to load it. # LoadError will be raised if that fails. def generate_secret_with_openssl require 'openssl' if !File.exist?("/dev/urandom") # OpenSSL transparently seeds the random number generator with # data from /dev/urandom. On platforms where that is not # available, such as Windows, we have to provide OpenSSL with # our own seed. Unfortunately there's no way to provide a # secure seed without OS support, so we'll have to do with # rand() and Time.now.usec(). OpenSSL::Random.seed(rand(0).to_s + Time.now.usec.to_s) end data = OpenSSL::BN.rand(2048, -1, false).to_s if OpenSSL::OPENSSL_VERSION_NUMBER > 0x00908000 OpenSSL::Digest::SHA512.new(data).hexdigest else generate_secret_with_prng end end # Generate a random secret key with /dev/urandom. # Raises SystemCallError on failure. def generate_secret_with_urandom return File.read("/dev/urandom", 64).unpack("H*")[0] end # Generate a random secret key with Ruby's pseudo random number generator, # as well as some environment information. # # This is the least cryptographically secure way to generate a secret key, # and should be avoided whenever possible. def generate_secret_with_prng require 'digest/sha2' sha = Digest::SHA2.new(512) now = Time.now sha << now.to_s sha << String(now.usec) sha << String(rand(0)) sha << String($$) sha << @identifier return sha.hexdigest end private def lastWin32ErrorMessage # Following code is based on David Garamond's GUID library for Ruby. get_last_error = Win32API.new("kernel32", "GetLastError", '', 'L') format_message = Win32API.new("kernel32", "FormatMessageA", 'LPLLPLPPPPPPPP', 'L') format_message_ignore_inserts = 0x00000200 format_message_from_system = 0x00001000 code = get_last_error.call msg = "\0" * 1024 len = format_message.call(format_message_ignore_inserts + format_message_from_system, 0, code, 0, msg, 1024, nil, nil, nil, nil, nil, nil, nil, nil) msg[0, len].tr("\r", '').chomp end def self.supports_secure_random? begin require 'securerandom' true rescue LoadError false end end def self.supports_win32_api? return false unless RUBY_PLATFORM =~ /(:?mswin|mingw)/ begin require 'Win32API' true rescue LoadError false end end def self.supports_urandom? File.exist?('/dev/urandom') end def self.supports_openssl? begin require 'openssl' true rescue LoadError false end end def self.supports_prng? true end end end