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"
...
Methods
B
H
R
Class Public methods
base64(n=nil)

::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.

# File activesupport/lib/active_support/secure_random.rb, line 151
def self.base64(n=nil)
  [random_bytes(n)].pack("m*").delete("\n")
end
hex(n=nil)

::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.

# File activesupport/lib/active_support/secure_random.rb, line 137
def self.hex(n=nil)
  random_bytes(n).unpack("H*")[0]
end
random_bytes(n=nil)

::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.

# File activesupport/lib/active_support/secure_random.rb, line 59
def self.random_bytes(n=nil)
  n ||= 16
  unless defined? OpenSSL
    begin
      require 'openssl'
    rescue LoadError
    end
  end
  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)

::random_number generates a random number.

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

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

# File activesupport/lib/active_support/secure_random.rb, line 164
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