Documentation for BN_is_prime_fasttest.

CHANGES

@@ -20,11 +20,15 @@
      generation becomes much faster.
 
      This implies a change for the callback functions in DSA_is_prime
-     and DSA_generate_parameters: They are now called once for each
-     positive witness in the Rabin-Miller test, not just occasionally
-     in the inner loop; and the parameters to the callback function now
-     provide an iteration count for the outer loop rather than for the
-     current invocation of the inner loop.
+     and DSA_generate_parameters: The callback function is called once
+     for each positive witness in the Rabin-Miller test, not just
+     occasionally in the inner loop; and the parameters to the
+     callback function now provide an iteration count for the outer
+     loop rather than for the current invocation of the inner loop.
+     DSA_generate_parameters additionally can call the callback
+     function with an 'iteration count' of -1, meaning that a
+     candidate has passed the trial division test (when q is generated 
+     from an application-provided seed, trial division is skipped).
      [Bodo Moeller]
 
   *) New function BN_is_prime_fasttest that optionally does trial

doc/crypto/BN_generate_prime.pod

@@ -2,7 +2,7 @@
 
 =head1 NAME
 
-BN_generate_prime, BN_is_prime - Generate primes and test for primality
+BN_generate_prime, BN_is_prime, BN_is_prime_fasttest - Generate primes and test for primality
 
 =head1 SYNOPSIS
 
@@ -14,11 +14,14 @@ BN_generate_prime, BN_is_prime - Generate primes and test for primality
  int BN_is_prime(BIGNUM *a, int checks, void (*callback)(int, int, 
      void *), BN_CTX *ctx, void *cb_arg);
 
+ int BN_is_prime_fasttest(BIGNUM *a, int checks, void (*callback)(int, int, 
+     void *), BN_CTX *ctx, BN_CTX *ctx2, void *cb_arg, int do_trial_division);
+
 =head1 DESCRIPTION
 
 BN_generate_prime() generates a pseudo-random prime number of B<num>
 bits.
-If B<ret> is not NULL, it will be used to store the number.
+If B<ret> is not B<NULL>, it will be used to store the number.
 
 If B<callback> is not B<NULL>, it is called as follows:
 
@@ -43,8 +46,8 @@ When a prime has been found, B<callback(2, i, cb_arg)> is called.
 The prime may have to fulfill additional requirements for use in
 Diffie-Hellman key exchange:
 
-If B<add> is not NULL, the prime will fulfill the condition p % B<add>
-== B<rem> (p % B<add> == 1 if B<rem> == NULL) in order to suit a given
+If B<add> is not B<NULL>, the prime will fulfill the condition p % B<add>
+== B<rem> (p % B<add> == 1 if B<rem> == B<NULL>) in order to suit a given
 generator.
 
 If B<safe> is true, it will be a safe prime (i.e. a prime p so
@@ -53,20 +56,40 @@ that (p-1)/2 is also prime).
 The PRNG must be seeded prior to calling BN_generate_prime().
 The prime number generation has a negligible error probability.
 
-BN_is_prime() tests if the number B<a> is prime. This is done by
-performing a Miller-Rabin probabilistic primality test with B<checks>
-iterations. If B<checks == BN_prime_check>, it uses a number
-of iterations that yields a false positive rate of at most 2^-80 for
-random input.
+BN_is_prime() and BN_is_prime_fasttest test if the number B<a> is
+prime.  The following tests are performed until one of them shows that
+B<a> is composite; if B<a> passes all these tests, it is considered
+prime.
+
+=over 4
+
+=item *
+
+BN_is_prime_fasttest(), when called with B<do_trial_division == 1>,
+first attempts trial division by a number of small primes;
+if no divisors are found by this test and B<callback> is not B<NULL>,
+B<callback(1, -1, cb_arg)> is called.
+If B<do_trial_division == 0>, this test is skipped.
+
+=item *
+
+Both BN_is_prime() and BN_is_prime_fasttest() perform a Miller-Rabin
+probabilistic primality test with B<checks> iterations. If
+B<checks == BN_prime_check>, a number of iterations is used that
+yields a false positive rate of at most 2^-80 for random input.
 
 If B<callback> is not B<NULL>, B<callback(1, j, cb_arg)> is called
-after the j-th iteration. B<ctx> is a pre-allocated B<BN_CTX> (to save
-the overhead of allocating and freeing the structure in a loop), or
-NULL.
+after the j-th iteration (j = 0, 1, ...). B<ctx> is a
+pre-allocated B<BN_CTX> (to save the overhead of allocating and
+freeing the structure in a loop), or B<NULL>. For
+BN_is_prime_fasttest(), B<ctx2> is a second pre-allocated B<BN_CTX> or
+B<NULL> (lacking this parameter, BN_is_prime() always has to allocated
+an additional B<CN_CTX>).
+
 
 =head1 RETURN VALUES
 
-BN_generate_prime() returns the prime number on success, NULL otherwise.
+BN_generate_prime() returns the prime number on success, B<NULL> otherwise.
 
 BN_is_prime() returns 0 if the number is composite, 1 if it is
 prime with an error probability of less than 0.25^B<checks>, and
@@ -83,5 +106,6 @@ L<bn(3)|bn(3)>, L<err(3)|err(3)>, L<rand(3)|rand(3)>
 The B<cb_arg> arguments to BN_generate_prime() and to BN_is_prime()
 were added in SSLeay 0.9.0. The B<ret> argument to BN_generate_prime()
 was added in SSLeay 0.9.1.
+BN_is_prime_fasttest() was added in OpenSSL 0.9.5.
 
 =cut