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author | René Korthaus <[email protected]> | 2016-03-08 09:30:40 +0100 |
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committer | René Korthaus <[email protected]> | 2016-03-08 09:30:40 +0100 |
commit | a60965ac6329e970491d315a02a3d328d9d4bb99 (patch) | |
tree | af06150ef518b51ff64debaae2818c8ad49842ef /doc/manual | |
parent | 58c89ae470c68bf300ea937740c233e2b5715535 (diff) |
Add section on fork safety to rng manual
Diffstat (limited to 'doc/manual')
-rw-r--r-- | doc/manual/rng.rst | 19 |
1 files changed, 19 insertions, 0 deletions
diff --git a/doc/manual/rng.rst b/doc/manual/rng.rst index 1ec37b52f..300570c3a 100644 --- a/doc/manual/rng.rst +++ b/doc/manual/rng.rst @@ -127,3 +127,22 @@ has been hashed by the ``RandomNumberGenerator`` that asked for the entropy, thus any hashing you do will be wasteful of both CPU cycles and entropy. +Fork Safety +--------------------------------- + +On Unix platforms, the ``fork()`` and ``clone()`` system calls can +be used to spawn a new child process. Fork safety ensures that the +child process doesn't see the same output of random bytes as the +parent process. Botan tries to ensure fork safety by feeding the +process ID into the internal state of the random generator and by +automatically reseeding the random generator if the process ID +changed between two requests of random bytes. However, this does +not protect against PID wrap around. The process ID is usually +implemented as a 16 bit integer. In this scenario, a process will +spawn a new child process, which exits the parent process and +spawns a new child process himself. If the PID wrapped around, the +second child process may get assigned the process ID of it's +grandparent and the fork safety can not be ensured. + +Therefore, it is strongly recommended to explicitly reseed the +random generator after forking a new process. |