securerandom.rb を 1.8 に追加し、cgi/session.rb に使わせたい のですが、どうでしょうか。 cgi/session.rb に限りませんが、session cookie の生成には暗号 学的にそれなりに安全な乱数が必要です。 しかし、現状の Ruby ではそのような安全な乱数を得る簡単な API が用意されていないため、安全なんかどうなのかよくわからない怪 しげなコードで session cookie を生成することがあります。 やはり、そういう難しい暗号の話は、餅は餅屋ということで外部 (OpenSSL や /dev/urandom) にまかせるのがいいのではないでしょ うか。 Index: lib/securerandom.rb =================================================================== --- lib/securerandom.rb (リビジョン 0) +++ lib/securerandom.rb (リビジョン 0) @@ -0,0 +1,137 @@ +# = 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 +# +# == 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" +# ... + +begin + require 'openssl' +rescue LoadError +end + +module SecureRandom + # 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. + 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 + @has_urandom = false + 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 + raise NotImplementedError, "No random device" + end + end + raise NotImplementedError, "No random device" + end + + # 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. + def self.hex(n=nil) + random_bytes(n).unpack("H*")[0] + end + + # 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. + def self.base64(n=nil) + [random_bytes(n)].pack("m*").delete("\n") + end + + # 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. + 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).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 +end Index: lib/cgi/session.rb =================================================================== --- lib/cgi/session.rb (リビジョン 13603) +++ lib/cgi/session.rb (作業コピー) @@ -174,16 +174,22 @@ # is used internally for automatically generated # session ids. def create_new_id - require 'digest/md5' - md5 = Digest::MD5::new - now = Time::now - md5.update(now.to_s) - md5.update(String(now.usec)) - md5.update(String(rand(0))) - md5.update(String($$)) - md5.update('foobar') + require 'securerandom' + begin + session_id = SecureRandom.hex(16) + rescue NotImplementedError + require 'digest/md5' + md5 = Digest::MD5::new + now = Time::now + md5.update(now.to_s) + md5.update(String(now.usec)) + md5.update(String(rand(0))) + md5.update(String($$)) + md5.update('foobar') + session_id = md5.hexdigest + end @new_session = true - md5.hexdigest + session_id end private :create_new_id -- [田中 哲][たなか あきら][Tanaka Akira]