RAND_egd.pod 3.2 KB

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