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