Module: ActiveSupport::SecureRandom

Defined in:
lib/active_support/secure_random.rb

Overview

Secure random number generator interface.

This library is an interface for secure random number generator which is suitable for generating session key in HTTP cookies, etc.

It supports following secure random number generators.

  • openssl

  • /dev/urandom

  • Win32

Note: This module is based on the SecureRandom library from Ruby 1.9, revision 18786, August 23 2008. It’s 100% interface-compatible with Ruby 1.9’s SecureRandom library.

Example

# random hexadecimal string.
p SecureRandom.hex(10) #=> "52750b30ffbc7de3b362"
p SecureRandom.hex(10) #=> "92b15d6c8dc4beb5f559"
p SecureRandom.hex(11) #=> "6aca1b5c58e4863e6b81b8"
p SecureRandom.hex(12) #=> "94b2fff3e7fd9b9c391a2306"
p SecureRandom.hex(13) #=> "39b290146bea6ce975c37cfc23"
...

# random base64 string.
p SecureRandom.base64(10) #=> "EcmTPZwWRAozdA=="
p SecureRandom.base64(10) #=> "9b0nsevdwNuM/w=="
p SecureRandom.base64(10) #=> "KO1nIU+p9DKxGg=="
p SecureRandom.base64(11) #=> "l7XEiFja+8EKEtY="
p SecureRandom.base64(12) #=> "7kJSM/MzBJI+75j8"
p SecureRandom.base64(13) #=> "vKLJ0tXBHqQOuIcSIg=="
...

# random binary string.
p SecureRandom.random_bytes(10) #=> "\016\t{\370g\310pbr\301"
p SecureRandom.random_bytes(10) #=> "\323U\030TO\234\357\020\a\337"
...

Class Method Summary collapse

Class Method Details

.base64(n = nil) ⇒ Object

SecureRandom.base64 generates a random base64 string.

The argument n specifies the length of the random length. The length of the result string is about 4/3 of n.

If n is not specified, 16 is assumed. It may be larger in future.

If secure random number generator is not available, NotImplementedError is raised.



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# File 'lib/active_support/secure_random.rb', line 149

def self.base64(n=nil)
  [random_bytes(n)].pack("m*").delete("\n")
end

.hex(n = nil) ⇒ Object

SecureRandom.hex generates a random hex string.

The argument n specifies the length of the random length. The length of the result string is twice of n.

If n is not specified, 16 is assumed. It may be larger in future.

If secure random number generator is not available, NotImplementedError is raised.



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# File 'lib/active_support/secure_random.rb', line 135

def self.hex(n=nil)
  random_bytes(n).unpack("H*")[0]
end

.lastWin32ErrorMessage ⇒ Object

Following code is based on David Garamond’s GUID library for Ruby.



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# File 'lib/active_support/secure_random.rb', line 184

def self.lastWin32ErrorMessage # :nodoc:
  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

.random_bytes(n = nil) ⇒ Object

SecureRandom.random_bytes generates a random binary string.

The argument n specifies the length of the result string.

If n is not specified, 16 is assumed. It may be larger in future.

If secure random number generator is not available, NotImplementedError is raised.

Raises:

  • (NotImplementedError) 


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# File 'lib/active_support/secure_random.rb', line 64

def self.random_bytes(n=nil)
  n ||= 16

  if defined? OpenSSL::Random
    return OpenSSL::Random.random_bytes(n)
  end

  if !defined?(@has_urandom) || @has_urandom
    flags = File::RDONLY
    flags |= File::NONBLOCK if defined? File::NONBLOCK
    flags |= File::NOCTTY if defined? File::NOCTTY
    flags |= File::NOFOLLOW if defined? File::NOFOLLOW
    begin
      File.open("/dev/urandom", flags) {|f|
        unless f.stat.chardev?
          raise Errno::ENOENT
        end
        @has_urandom = true
        ret = f.readpartial(n)
        if ret.length != n
          raise NotImplementedError, "Unexpected partial read from random device"
        end
        return ret
      }
    rescue Errno::ENOENT
      @has_urandom = false
    end
  end

  if !defined?(@has_win32)
    begin
      require 'Win32API'

      crypt_acquire_context = Win32API.new("advapi32", "CryptAcquireContext", 'PPPII', 'L')
      @crypt_gen_random = Win32API.new("advapi32", "CryptGenRandom", 'LIP', 'L')

      hProvStr = " " * 4
      prov_rsa_full = 1
      crypt_verifycontext = 0xF0000000

      if crypt_acquire_context.call(hProvStr, nil, nil, prov_rsa_full, crypt_verifycontext) == 0
        raise SystemCallError, "CryptAcquireContext failed: #{lastWin32ErrorMessage}"
      end
      @hProv, = hProvStr.unpack('L')

      @has_win32 = true
    rescue LoadError
      @has_win32 = false
    end
  end
  if @has_win32
    bytes = " " * n
    if @crypt_gen_random.call(@hProv, bytes.size, bytes) == 0
      raise SystemCallError, "CryptGenRandom failed: #{lastWin32ErrorMessage}"
    end
    return bytes
  end

  raise NotImplementedError, "No random device"
end

.random_number(n = 0) ⇒ Object

SecureRandom.random_number generates a random number.

If an positive integer is given as n, SecureRandom.random_number returns an integer: 0 <= SecureRandom.random_number(n) < n.

If 0 is given or an argument is not given, SecureRandom.random_number returns an float: 0.0 <= SecureRandom.random_number() < 1.0.



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# File 'lib/active_support/secure_random.rb', line 162

def self.random_number(n=0)
  if 0 < n
    hex = n.to_s(16)
    hex = '0' + hex if (hex.length & 1) == 1
    bin = [hex].pack("H*")
    mask = bin[0]
    mask |= mask >> 1
    mask |= mask >> 2
    mask |= mask >> 4
    begin
      rnd = SecureRandom.random_bytes(bin.length)
      rnd[0] = rnd[0] & mask
    end until rnd < bin
    rnd.unpack("H*")[0].hex
  else
    # assumption: Float::MANT_DIG <= 64
    i64 = SecureRandom.random_bytes(8).unpack("Q")[0]
    Math.ldexp(i64 >> (64-Float::MANT_DIG), -Float::MANT_DIG)
  end
end