openssl/doc/man3/RAND_egd.pod

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=head1 NAME

RAND_egd, RAND_egd_bytes, RAND_query_egd_bytes - query entropy gathering daemon

=head1 SYNOPSIS

 #include <openssl/rand.h>

 int RAND_egd_bytes(const char *path, int num);
 int RAND_egd(const char *path);

 int RAND_query_egd_bytes(const char *path, unsigned char *buf, int num);

=head1 DESCRIPTION

On older platforms without a good source of randomness such as C</dev/urandom>,
it is possible to query an Entropy Gathering Daemon (EGD) over a local
socket to obtain randomness and seed the OpenSSL RNG.
The protocol used is defined by the EGDs available at
L<http://egd.sourceforge.net/> or L<http://prngd.sourceforge.net>.

RAND_egd_bytes() requests B<num> bytes of randomness from an EGD at the
specified socket B<path>, and passes the data it receives into RAND_add().
RAND_egd() is equivalent to RAND_egd_bytes() with B<num> set to 255.

RAND_query_egd_bytes() requests B<num> bytes of randomness from an EGD at
the specified socket B<path>, where B<num> must be less than 256.
If B<buf> is B<NULL>, it is equivalent to RAND_egd_bytes().
If B<buf> is not B<NULL>, then the data is copied to the buffer and
RAND_add() is not called.

OpenSSL can be configured at build time to try to use the EGD for seeding
automatically.

=head1 RETURN VALUES

RAND_egd() and RAND_egd_bytes() return the number of bytes read from the
daemon on success, or -1 if the connection failed or the daemon did not
return enough data to fully seed the PRNG.

RAND_query_egd_bytes() returns the number of bytes read from the daemon on
success, or -1 if the connection failed.

=head1 SEE ALSO

L<RAND_bytes(3)>, L<RAND_add(3)>

=head1 COPYRIGHT

Copyright 2000-2017 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the OpenSSL license (the "License").  You may not use
this file except in compliance with the License.  You can obtain a copy
in the file LICENSE in the source distribution or at
L<https://www.openssl.org/source/license.html>.

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