# = Secure random number generator interface.

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#

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# This library is an interface for secure random number generator which is

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# suitable for generating session key in HTTP cookies, etc.

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#

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# It supports following secure random number generators.

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#

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# * openssl

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# * /dev/urandom

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#

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# == Example

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#

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# # random hexadecimal string.

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# p SecureRandom.hex(10) #=> "52750b30ffbc7de3b362"

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# p SecureRandom.hex(10) #=> "92b15d6c8dc4beb5f559"

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# p SecureRandom.hex(11) #=> "6aca1b5c58e4863e6b81b8"

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# p SecureRandom.hex(12) #=> "94b2fff3e7fd9b9c391a2306"

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# p SecureRandom.hex(13) #=> "39b290146bea6ce975c37cfc23"

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# ...

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#

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# # random base64 string.

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# p SecureRandom.base64(10) #=> "EcmTPZwWRAozdA=="

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# p SecureRandom.base64(10) #=> "9b0nsevdwNuM/w=="

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# p SecureRandom.base64(10) #=> "KO1nIU+p9DKxGg=="

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# p SecureRandom.base64(11) #=> "l7XEiFja+8EKEtY="

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

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# p SecureRandom.base64(13) #=> "vKLJ0tXBHqQOuIcSIg=="

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# ...

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#

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# # random binary string.

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# p SecureRandom.random_bytes(10) #=> "\016\t{\370g\310pbr\301"

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# p SecureRandom.random_bytes(10) #=> "\323U\030TO\234\357\020\a\337"

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# ...

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begin

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require 'openssl'

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rescue LoadError

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end

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module SecureRandom

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# SecureRandom.random_bytes generates a random binary string.

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#

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# The argument n specifies the length of the result string.

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#

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# If n is not specified, 16 is assumed.

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# It may be larger in future.

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#

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# If secure random number generator is not available,

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# NotImplementedError is raised.

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def self.random_bytes(n=nil)

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n ||= 16

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if defined? OpenSSL::Random

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@pid = 0 if !defined?(@pid)

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pid = $$

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if @pid != pid

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now = Time.now

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ary = [now.to_i, now.usec, @pid, pid]

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OpenSSL::Random.seed(ary.join('.'))

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@pid = pid

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end

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return OpenSSL::Random.random_bytes(n)

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end

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if !defined?(@has_urandom) || @has_urandom

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@has_urandom = false

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flags = File::RDONLY

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flags |= File::NONBLOCK if defined? File::NONBLOCK

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flags |= File::NOCTTY if defined? File::NOCTTY

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flags |= File::NOFOLLOW if defined? File::NOFOLLOW

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begin

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File.open("/dev/urandom", flags) {|f|

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unless f.stat.chardev?

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raise Errno::ENOENT

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end

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@has_urandom = true

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ret = f.readpartial(n)

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if ret.length != n

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raise NotImplementedError, "Unexpected partial read from random device"

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end

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return ret

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}

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rescue Errno::ENOENT

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raise NotImplementedError, "No random device"

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end

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end

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raise NotImplementedError, "No random device"

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end

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# SecureRandom.hex generates a random hex string.

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#

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# The argument n specifies the length of the random length.

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# The length of the result string is twice of n.

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#

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# If n is not specified, 16 is assumed.

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# It may be larger in future.

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#

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# If secure random number generator is not available,

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# NotImplementedError is raised.

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def self.hex(n=nil)

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random_bytes(n).unpack("H*")[0]

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end

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# SecureRandom.base64 generates a random base64 string.

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#

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# The argument n specifies the length of the random length.

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# The length of the result string is about 4/3 of n.

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#

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# If n is not specified, 16 is assumed.

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# It may be larger in future.

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#

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# If secure random number generator is not available,

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# NotImplementedError is raised.

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def self.base64(n=nil)

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[random_bytes(n)].pack("m*").delete("\n")

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end

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# SecureRandom.random_number generates a random number.

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#

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# If an positive integer is given as n,

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# SecureRandom.random_number returns an integer:

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# 0 <= SecureRandom.random_number(n) < n.

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#

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# If 0 is given or an argument is not given,

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# SecureRandom.random_number returns an float:

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# 0.0 <= SecureRandom.random_number() < 1.0.

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def self.random_number(n=0)

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if 0 < n

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hex = n.to_s(16)

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hex = '0' + hex if (hex.length & 1) == 1

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bin = [hex].pack("H*")

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mask = bin[0]

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mask |= mask >> 1

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mask |= mask >> 2

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mask |= mask >> 4

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begin

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rnd = SecureRandom.random_bytes(bin.length)

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rnd[0] = (rnd[0] & mask).chr

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end until rnd < bin

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rnd.unpack("H*")[0].hex

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else

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# assumption: Float::MANT_DIG <= 64

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i64 = SecureRandom.random_bytes(8).unpack("Q")[0]

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Math.ldexp(i64 >> (64-Float::MANT_DIG), -Float::MANT_DIG)

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end

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end

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end

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