Re: [Boost-bugs] [Boost C++ Libraries] #5187: uuid\seed_rng.hpp sha1_random_digest_state_ not random

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #5187: uuid\seed_rng.hpp sha1_random_digest_state_ not random
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2011-02-15 01:15:59

#5187: uuid\seed_rng.hpp sha1_random_digest_state_ not random
--------------------------------------------+-------------------------------
  Reporter:  qiaozhiqiang@…                 |       Owner:          
      Type:  Bugs                           |      Status:  new     
 Milestone:  To Be Determined               |   Component:  None    
   Version:  Boost 1.45.0                   |    Severity:  Problem 
Resolution:                                 |    Keywords:  seed_rng
--------------------------------------------+-------------------------------

Comment (by qiaozhiqiang@…):

 see this:

 boost_1_45_0\boost\uuid\seed_rng.hpp

  first time, state is all zero,sha1_random_digest_() will modify it.
 but always return the same pointer of static value, so ps is not random.

 {{{


  static unsigned int * sha1_random_digest_state_()
      {
          // intentionally left uninitialized

          ///////////
          // !!!!!!!!  first time, state is all zero,sha1_random_digest_()
 will modify it.
          // but always return the same pointer of static value
          ///////////
          static unsigned int state[ 5 ];
          return state;
      }


  unsigned int * ps = sha1_random_digest_state_();

          unsigned int state[ 5 ];

          std::memcpy( state, ps, sizeof( state ) ); // harmless data race

          sha.process_bytes( (unsigned char const*)state, sizeof( state )
 );

         /////////////////
         // !!!!!!!!  ERROR: sha1_random_digest_state_() always return the
 same pointer of the static value
         // so should delete next line??
          ////////////////
          sha.process_bytes( (unsigned char const*)&ps, sizeof( ps ) );

  namespace boost {
  namespace uuids {
  namespace detail {

  // should this be part of Boost.Random?
  class seed_rng
  {
  static unsigned int * sha1_random_digest_state_()
      {
          // intentionally left uninitialized
          static unsigned int state[ 5 ];
          return state;
      }

      void sha1_random_digest_()
      {
          boost::uuids::detail::sha1 sha;

          unsigned int * ps = sha1_random_digest_state_();

          unsigned int state[ 5 ];
          std::memcpy( state, ps, sizeof( state ) ); // harmless data race

          sha.process_bytes( (unsigned char const*)state, sizeof( state )
 );
          sha.process_bytes( (unsigned char const*)&ps, sizeof( ps ) );

 }}}

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/5187#comment:1>
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