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author | marha <marha@users.sourceforge.net> | 2009-06-28 22:07:26 +0000 |
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committer | marha <marha@users.sourceforge.net> | 2009-06-28 22:07:26 +0000 |
commit | 3562e78743202e43aec8727005182a2558117eca (patch) | |
tree | 8f9113a77d12470c5c851a2a8e4cb02e89df7d43 /openssl/doc/crypto/RAND_add.pod | |
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Diffstat (limited to 'openssl/doc/crypto/RAND_add.pod')
-rw-r--r-- | openssl/doc/crypto/RAND_add.pod | 77 |
1 files changed, 77 insertions, 0 deletions
diff --git a/openssl/doc/crypto/RAND_add.pod b/openssl/doc/crypto/RAND_add.pod new file mode 100644 index 000000000..67c66f3e0 --- /dev/null +++ b/openssl/doc/crypto/RAND_add.pod @@ -0,0 +1,77 @@ +=pod + +=head1 NAME + +RAND_add, RAND_seed, RAND_status, RAND_event, RAND_screen - add +entropy to the PRNG + +=head1 SYNOPSIS + + #include <openssl/rand.h> + + void RAND_seed(const void *buf, int num); + + void RAND_add(const void *buf, int num, double entropy); + + int RAND_status(void); + + int RAND_event(UINT iMsg, WPARAM wParam, LPARAM lParam); + void RAND_screen(void); + +=head1 DESCRIPTION + +RAND_add() mixes the B<num> bytes at B<buf> into the PRNG state. Thus, +if the data at B<buf> are unpredictable to an adversary, this +increases the uncertainty about the state and makes the PRNG output +less predictable. Suitable input comes from user interaction (random +key presses, mouse movements) and certain hardware events. The +B<entropy> argument is (the lower bound of) an estimate of how much +randomness is contained in B<buf>, measured in bytes. Details about +sources of randomness and how to estimate their entropy can be found +in the literature, e.g. RFC 1750. + +RAND_add() may be called with sensitive data such as user entered +passwords. The seed values cannot be recovered from the PRNG output. + +OpenSSL makes sure that the PRNG state is unique for each thread. On +systems that provide C</dev/urandom>, the randomness device is used +to seed the PRNG transparently. However, on all other systems, the +application is responsible for seeding the PRNG by calling RAND_add(), +L<RAND_egd(3)|RAND_egd(3)> +or L<RAND_load_file(3)|RAND_load_file(3)>. + +RAND_seed() is equivalent to RAND_add() when B<num == entropy>. + +RAND_event() collects the entropy from Windows events such as mouse +movements and other user interaction. It should be called with the +B<iMsg>, B<wParam> and B<lParam> arguments of I<all> messages sent to +the window procedure. It will estimate the entropy contained in the +event message (if any), and add it to the PRNG. The program can then +process the messages as usual. + +The RAND_screen() function is available for the convenience of Windows +programmers. It adds the current contents of the screen to the PRNG. +For applications that can catch Windows events, seeding the PRNG by +calling RAND_event() is a significantly better source of +randomness. It should be noted that both methods cannot be used on +servers that run without user interaction. + +=head1 RETURN VALUES + +RAND_status() and RAND_event() return 1 if the PRNG has been seeded +with enough data, 0 otherwise. + +The other functions do not return values. + +=head1 SEE ALSO + +L<rand(3)|rand(3)>, L<RAND_egd(3)|RAND_egd(3)>, +L<RAND_load_file(3)|RAND_load_file(3)>, L<RAND_cleanup(3)|RAND_cleanup(3)> + +=head1 HISTORY + +RAND_seed() and RAND_screen() are available in all versions of SSLeay +and OpenSSL. RAND_add() and RAND_status() have been added in OpenSSL +0.9.5, RAND_event() in OpenSSL 0.9.5a. + +=cut |