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61 lines
2.0 KiB
Plaintext
61 lines
2.0 KiB
Plaintext
=pod
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=head1 NAME
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RAND_add, RAND_seed, RAND_screen - Add 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, int entropy);
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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>. Details about sources of randomness
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and how to estimate their entropy can be found in the literature,
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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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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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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 with
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the parameters of B<WM_MOUSEMOVE> events is a significantly better
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source of randomness. It should be noted that both methods cannot be
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used on servers that run without user interaction.
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=head1 RETURN VALUES
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These functions do not return values.
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=head1 SEE ALSO
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L<rand(3)|rand(3)>, 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() was added in OpenSSL 0.9.5.
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=cut
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