Module: SecureRandom

Defined in:
lib/securerandom.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

Examples

Hexadecimal string.

p SecureRandom.hex(10) #=> "52750b30ffbc7de3b362"
p SecureRandom.hex(10) #=> "92b15d6c8dc4beb5f559"
p SecureRandom.hex(13) #=> "39b290146bea6ce975c37cfc23"

Base64 string.

p SecureRandom.base64(10) #=> "EcmTPZwWRAozdA=="
p SecureRandom.base64(10) #=> "KO1nIU+p9DKxGg=="
p SecureRandom.base64(12) #=> "7kJSM/MzBJI+75j8"

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

+ (Object) base64(n = nil)

SecureRandom.base64 generates a random base64 string.

The argument n specifies the length, in bytes, of the random number to be generated. The length of the result string is about 4/3 of n.

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

The result may contain A-Z, a-z, 0-9, “+”, “/” and “=”.

p SecureRandom.base64 #=> "/2BuBuLf3+WfSKyQbRcc/A=="
p SecureRandom.base64 #=> "6BbW0pxO0YENxn38HMUbcQ=="

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

See RFC 3548 for the definition of base64.



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# File 'lib/securerandom.rb', line 155

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

+ (Object) hex(n = nil)

SecureRandom.hex generates a random hexadecimal string.

The argument n specifies the length, in bytes, of the random number to be generated. The length of the resulting hexadecimal string is twice n.

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

The result may contain 0-9 and a-f.

p SecureRandom.hex #=> "eb693ec8252cd630102fd0d0fb7c3485"
p SecureRandom.hex #=> "91dc3bfb4de5b11d029d376634589b61"

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



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# File 'lib/securerandom.rb', line 134

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

+ (Object) lastWin32ErrorMessage

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



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# File 'lib/securerandom.rb', line 249

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].force_encoding("filesystem").tr("\r", '').chomp
end

+ (Object) random_bytes(n = nil)

SecureRandom.random_bytes generates a random binary string.

The argument n specifies the length of the result string.

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

The result may contain any byte: “x00” - “xff”.

p SecureRandom.random_bytes #=> "\xD8\\\xE0\xF4\r\xB2\xFC*WM\xFF\x83\x18\xF45\xB6"
p SecureRandom.random_bytes #=> "m\xDC\xFC/\a\x00Uf\xB2\xB2P\xBD\xFF6S\x97"

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

Raises:

  • (NotImplementedError)


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# File 'lib/securerandom.rb', line 50

def self.random_bytes(n=nil)
  n = n ? n.to_int : 16

  if defined? OpenSSL::Random
    @pid = 0 unless defined?(@pid)
    pid = $$
    unless @pid == pid
      now = Process.clock_gettime(Process::CLOCK_REALTIME, :nanosecond)
      ary = [now, @pid, pid]
      OpenSSL::Random.random_add(ary.join("").to_s, 0.0)
      @pid = pid
    end
    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
    begin
      File.open("/dev/urandom", flags) {|f|
        unless f.stat.chardev?
          raise Errno::ENOENT
        end
        @has_urandom = true
        ret = f.read(n)
        unless ret.length == n
          raise NotImplementedError, "Unexpected partial read from random device: only #{ret.length} for #{n} bytes"
        end
        return ret
      }
    rescue Errno::ENOENT
      @has_urandom = false
    end
  end

  unless defined?(@has_win32)
    begin
      require 'Win32API'

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

      hProvStr = " " * DL::SIZEOF_VOIDP
      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
      type = DL::SIZEOF_VOIDP == DL::SIZEOF_LONG_LONG ? 'q' : 'l'
      @hProv, = hProvStr.unpack(type)

      @has_win32 = true
    rescue LoadError
      @has_win32 = false
    end
  end
  if @has_win32
    bytes = " ".force_encoding("ASCII-8BIT") * 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

+ (Object) random_number(n = 0)

SecureRandom.random_number generates a random number.

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

p SecureRandom.random_number(100) #=> 15
p SecureRandom.random_number(100) #=> 88

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

p SecureRandom.random_number #=> 0.596506046187744
p SecureRandom.random_number #=> 0.350621695741409


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# File 'lib/securerandom.rb', line 209

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].ord
    mask |= mask >> 1
    mask |= mask >> 2
    mask |= mask >> 4
    begin
      rnd = SecureRandom.random_bytes(bin.length)
      rnd[0] = (rnd[0].ord & mask).chr
    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

+ (Object) urlsafe_base64(n = nil, padding = false)

SecureRandom.urlsafe_base64 generates a random URL-safe base64 string.

The argument n specifies the length, in bytes, of the random number to be generated. The length of the result string is about 4/3 of n.

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

The boolean argument padding specifies the padding. If it is false or nil, padding is not generated. Otherwise padding is generated. By default, padding is not generated because “=” may be used as a URL delimiter.

The result may contain A-Z, a-z, 0-9, “-” and “_”. “=” is also used if padding is true.

p SecureRandom.urlsafe_base64 #=> "b4GOKm4pOYU_-BOXcrUGDg"
p SecureRandom.urlsafe_base64 #=> "UZLdOkzop70Ddx-IJR0ABg"

p SecureRandom.urlsafe_base64(nil, true) #=> "i0XQ-7gglIsHGV2_BNPrdQ=="
p SecureRandom.urlsafe_base64(nil, true) #=> "-M8rLhr7JEpJlqFGUMmOxg=="

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

See RFC 3548 for the definition of URL-safe base64.



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# File 'lib/securerandom.rb', line 185

def self.urlsafe_base64(n=nil, padding=false)
  s = [random_bytes(n)].pack("m*")
  s.delete!("\n")
  s.tr!("+/", "-_")
  s.delete!("=") unless padding
  s
end

+ (Object) uuid

SecureRandom.uuid generates a v4 random UUID (Universally Unique IDentifier).

p SecureRandom.uuid #=> "2d931510-d99f-494a-8c67-87feb05e1594"
p SecureRandom.uuid #=> "bad85eb9-0713-4da7-8d36-07a8e4b00eab"
p SecureRandom.uuid #=> "62936e70-1815-439b-bf89-8492855a7e6b"

The version 4 UUID is purely random (except the version). It doesn't contain meaningful information such as MAC address, time, etc.

See RFC 4122 for details of UUID.



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# File 'lib/securerandom.rb', line 241

def self.uuid
  ary = self.random_bytes(16).unpack("NnnnnN")
  ary[2] = (ary[2] & 0x0fff) | 0x4000
  ary[3] = (ary[3] & 0x3fff) | 0x8000
  "%08x-%04x-%04x-%04x-%04x%08x" % ary
end