RSA_generate_key() using prngd instead of /dev/random or /dev/urandom

Question

I want to use RSA_generate_key() on HP-UX 11.11. But hp-ux 11.11 does not provide /dev/random or /dev/urandom, so I need to use openssl prngd.

Please let me know how to use it by default in C code. I have openssl installed and prngd is available.

$ ls /opt/openssl/prngd/prngd  
/opt/openssl/prngd/prngd

Let me know if you need more information.

Answer 1

Noting that prngd uses the same interface that EGD does, checkout the instructions found here. A quote of interest is:

On systems without /dev/*random devices providing entropy from the kernel

Alternatively, the EGD-interface compatible daemon PRNGD can be used.

OpenSSL automatically queries EGD when entropy is requested via RAND_bytes() or the status is checked via RAND_status() for the first time, if the socket is located at /var/run/egd-pool, /dev/egd-pool or /etc/egd-pool.

So when you run prngd, run it as prngd /dev/egd-pool or one of the other alternatives

Answer 2

prngd simulates "/dev/random" and "/dev/urandom" over a network connection. It supports either a Unix stream-based domain socket ("/var/run/egd-pool") or (if configured to) or IP using TCP ports 708 or 4840 (default values---can be changed).

So, in using the Unix domain socket, it would look something like:

#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>

int devrandom(void)
{
  union 
  {
    struct sockaddr    sa;
    struct sockaddr_un path;
  } location;
  int sock;               

  memset(&location,0,sizeof(location));
  location.path.sun_family = AF_UNIX;
  strcpy(location.path.sun_path,"/var/run/egd-pool");

  sock = socket(AF_UNIX,SOCK_STREAM,0);
  if (sock < 0)
    return -1; 

  if (connect(sock,&location.sa,sizeof(struct sockaddr_un)) < 0)
    return -1;

  return sock;
}

This will return a file descriptor you can pass to read() in order to obtain the random data (note: this code is untested). A TCP/IP based connection is a bit more involved, requiring binding the socket to a local address and connecting to the remote address but there are plenty of examples on the Internet for that type of code.