This project produces nonce.a, a simple nonce management library that implements the concept of nonces as defined by DNSCurve (see http://dnscurve.org/).  All nonces are exactly 12-bytes.

There are four branches, all with the same interface but defining nonces in slightly different ways: 
	nonce12 - Uses a 12-byte counter starting from 0. Each time next_nonce is called, the nonce is incremented by one.
	nonce8rand4 - Uses an 8-byte counter starting from 0, plus a 4-byte random number. Each time next_nonce is called, the 8-byte counter is incremented by one, and the 4-byte random number is recalculated.
	tai12 - Uses a 12-byte TAI64N label (see http://cr.yp.to/proto/tai64.txt) re-calculated each time nonce_next is called.  If the time has not changed (in the unlikely case where nonce_next is called twice quickly in succession), the number is incremented to ensure a unique nonce.
	tai8rand4 - Uses an 8-byte TAI64 label (see http://cr.yp.to/proto/tai64.txt) plus a 4-byte random number. 

The header nonce.h has the following operations:

  void nonce_create(const char *filepath);
  void nonce_next(const char *filepath, char *nonce);
  void nonce_separate(char *nonce, int nserv,int serv);
  void nonce_show(const char *nonce);

A nonce is stored in a file, and the file must be accessed and updated each time a nonce is used, to prevent the same nonce number from being used twice.  

When a new nonce is needed, create a buffer of size NONCE_BYTES (defined in nonce.h), choose a filename, and call nonce_next. If the file does not yet exist, nonce_create will be called to create one for you. 

e.g.:

	char buf[NONCE_BYTES];
	nonce_next("mynonce",buf);

	/* buf now contains a unique nonce */

If you want to support nonce separation (see http://dnscurve.org/out-implement.html) use nonce_separate after each nonce_next.  The function nonce_separate takes two arguments: the total number of servers, and a zero-indexed number representing the current server:

	char buf[NONCE_BYTES];
	nonce_next("mynonce",buf);
	nonce_separate(50,4); /* we are server number 5 of 50 */