1=pod 2 3=head1 NAME 4 5RAND_egd, RAND_egd_bytes, RAND_query_egd_bytes - query entropy gathering daemon 6 7=head1 SYNOPSIS 8 9 #include <openssl/rand.h> 10 11 int RAND_egd(const char *path); 12 int RAND_egd_bytes(const char *path, int bytes); 13 14 int RAND_query_egd_bytes(const char *path, unsigned char *buf, int bytes); 15 16=head1 DESCRIPTION 17 18RAND_egd() queries the entropy gathering daemon EGD on socket B<path>. 19It queries 255 bytes and uses L<RAND_add(3)|RAND_add(3)> to seed the 20OpenSSL built-in PRNG. RAND_egd(path) is a wrapper for 21RAND_egd_bytes(path, 255); 22 23RAND_egd_bytes() queries the entropy gathering daemon EGD on socket B<path>. 24It queries B<bytes> bytes and uses L<RAND_add(3)|RAND_add(3)> to seed the 25OpenSSL built-in PRNG. 26This function is more flexible than RAND_egd(). 27When only one secret key must 28be generated, it is not necessary to request the full amount 255 bytes from 29the EGD socket. This can be advantageous, since the amount of entropy 30that can be retrieved from EGD over time is limited. 31 32RAND_query_egd_bytes() performs the actual query of the EGD daemon on socket 33B<path>. If B<buf> is given, B<bytes> bytes are queried and written into 34B<buf>. If B<buf> is NULL, B<bytes> bytes are queried and used to seed the 35OpenSSL built-in PRNG using L<RAND_add(3)|RAND_add(3)>. 36 37=head1 NOTES 38 39On systems without /dev/*random devices providing entropy from the kernel, 40the EGD entropy gathering daemon can be used to collect entropy. It provides 41a socket interface through which entropy can be gathered in chunks up to 42255 bytes. Several chunks can be queried during one connection. 43 44EGD is available from http://www.lothar.com/tech/crypto/ (C<perl 45Makefile.PL; make; make install> to install). It is run as B<egd> 46I<path>, where I<path> is an absolute path designating a socket. When 47RAND_egd() is called with that path as an argument, it tries to read 48random bytes that EGD has collected. RAND_egd() retrieves entropy from the 49daemon using the daemon's "non-blocking read" command which shall 50be answered immediately by the daemon without waiting for additional 51entropy to be collected. The write and read socket operations in the 52communication are blocking. 53 54Alternatively, the EGD-interface compatible daemon PRNGD can be used. It is 55available from 56http://prngd.sourceforge.net/ . 57PRNGD does employ an internal PRNG itself and can therefore never run 58out of entropy. 59 60OpenSSL automatically queries EGD when entropy is requested via RAND_bytes() 61or the status is checked via RAND_status() for the first time, if the socket 62is located at /var/run/egd-pool, /dev/egd-pool or /etc/egd-pool. 63 64=head1 RETURN VALUE 65 66RAND_egd() and RAND_egd_bytes() return the number of bytes read from the 67daemon on success, and -1 if the connection failed or the daemon did not 68return enough data to fully seed the PRNG. 69 70RAND_query_egd_bytes() returns the number of bytes read from the daemon on 71success, and -1 if the connection failed. The PRNG state is not considered. 72 73=head1 SEE ALSO 74 75L<rand(3)|rand(3)>, L<RAND_add(3)|RAND_add(3)>, 76L<RAND_cleanup(3)|RAND_cleanup(3)> 77 78=head1 HISTORY 79 80RAND_egd() is available since OpenSSL 0.9.5. 81 82RAND_egd_bytes() is available since OpenSSL 0.9.6. 83 84RAND_query_egd_bytes() is available since OpenSSL 0.9.7. 85 86The automatic query of /var/run/egd-pool et al was added in OpenSSL 0.9.7. 87 88=cut 89