- NAME
- SYNOPSIS
- DESCRIPTION
- RETURN VALUES
- SEE ALSO
- COPYRIGHT

# NAME

RAND_egd, RAND_egd_bytes, RAND_query_egd_bytes - query entropy gathering daemon

# 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);

# DESCRIPTION

On older platforms without a good source of randomness such as `/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 http://egd.sourceforge.net/ or http://prngd.sourceforge.net.

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

`RAND_query_egd_bytes()` requests num bytes of randomness from an EGD at the specified socket path, where num must be less than 256. If buf is NULL, it is equivalent to `RAND_egd_bytes()`. If buf is not 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.

# 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.

# SEE ALSO

RAND_add(3), RAND_bytes(3), RAND(7)

# COPYRIGHT

Copyright 2000-2018 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 https://www.openssl.org/source/license.html.