Make number of Miller-Rabin tests for a prime tests depend on the security level...

[openssl.git] / doc / man3 / BN_generate_prime.pod

diff --git a/doc/man3/BN_generate_prime.pod b/doc/man3/BN_generate_prime.pod
index fb492feb775b58e7f010ab7d8a040d16a326be9d..4b085e7400e1ce8b6013448a1d253be3ba7fc435 100644 (file)
--- a/doc/man3/BN_generate_prime.pod
+++ b/doc/man3/BN_generate_prime.pod
@@ -12,12 +12,12 @@ for primality
  #include <openssl/bn.h>
 
  int BN_generate_prime_ex(BIGNUM *ret, int bits, int safe, const BIGNUM *add,
-     const BIGNUM *rem, BN_GENCB *cb);
+                          const BIGNUM *rem, BN_GENCB *cb);
 
  int BN_is_prime_ex(const BIGNUM *p, int nchecks, BN_CTX *ctx, BN_GENCB *cb);
 
  int BN_is_prime_fasttest_ex(const BIGNUM *p, int nchecks, BN_CTX *ctx,
-     int do_trial_division, BN_GENCB *cb);
+                             int do_trial_division, BN_GENCB *cb);
 
  int BN_GENCB_call(BN_GENCB *cb, int a, int b);
 
@@ -26,10 +26,10 @@ for primality
  void BN_GENCB_free(BN_GENCB *cb);
 
  void BN_GENCB_set_old(BN_GENCB *gencb,
-     void (*callback)(int, int, void *), void *cb_arg);
+                       void (*callback)(int, int, void *), void *cb_arg);
 
  void BN_GENCB_set(BN_GENCB *gencb,
-     int (*callback)(int, int, BN_GENCB *), void *cb_arg);
+                   int (*callback)(int, int, BN_GENCB *), void *cb_arg);
 
  void *BN_GENCB_get_arg(BN_GENCB *cb);
 
@@ -37,14 +37,15 @@ Deprecated:
 
  #if OPENSSL_API_COMPAT < 0x00908000L
  BIGNUM *BN_generate_prime(BIGNUM *ret, int num, int safe, BIGNUM *add,
-     BIGNUM *rem, void (*callback)(int, int, void *), void *cb_arg);
+                           BIGNUM *rem, void (*callback)(int, int, void *),
+                           void *cb_arg);
 
- int BN_is_prime(const BIGNUM *a, int checks, void (*callback)(int, int,
-     void *), BN_CTX *ctx, void *cb_arg);
+ int BN_is_prime(const BIGNUM *a, int checks,
+                 void (*callback)(int, int, void *), BN_CTX *ctx, void *cb_arg);
 
  int BN_is_prime_fasttest(const BIGNUM *a, int checks,
-     void (*callback)(int, int, void *), BN_CTX *ctx, void *cb_arg,
-     int do_trial_division);
+                          void (*callback)(int, int, void *), BN_CTX *ctx,
+                          void *cb_arg, int do_trial_division);
  #endif
 
 =head1 DESCRIPTION
@@ -100,20 +101,30 @@ If B<do_trial_division == 0>, this test is skipped.
 Both BN_is_prime_ex() and BN_is_prime_fasttest_ex() perform a Miller-Rabin
 probabilistic primality test with B<nchecks> iterations. If
 B<nchecks == BN_prime_checks>, a number of iterations is used that
-yields a false positive rate of at most 2^-80 for random input.
+yields a false positive rate of at most 2^-64 for random input.
+The error rate depends on the size of the prime and goes down for bigger primes.
+The rate is 2^-80 starting at 308 bits, 2^-112 at 852 bit, 2^-128 at 1080 bits,
+2^-192 at 3747 bit and 2^-256 at 6394 bit.
+
+When the source of the prime is not random or not trusted, the number
+of checks needs to be much higher to reach the same level of assurance:
+It should equal half of the targeted security level in bits (rounded up to the
+next integer if necessary).
+For instance, to reach the 128 bit security level, B<nchecks> should be set to
+64.
 
 If B<cb> is not B<NULL>, B<BN_GENCB_call(cb, 1, j)> is called
 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>.
 
-BN_GENCB_call calls the callback function held in the B<BN_GENCB> structure
+BN_GENCB_call() calls the callback function held in the B<BN_GENCB> structure
 and passes the ints B<a> and B<b> as arguments. There are two types of
 B<BN_GENCB> structure that are supported: "new" style and "old" style. New
 programs should prefer the "new" style, whilst the "old" style is provided
 for backwards compatibility purposes.
 
-A BN_GENCB structure should be created through a call to BN_GENCB_new(),
+A B<BN_GENCB> structure should be created through a call to BN_GENCB_new(),
 and freed through a call to BN_GENCB_free().
 
 For "new" style callbacks a BN_GENCB structure should be initialised with a
@@ -130,12 +141,12 @@ style callbacks or B<callback(a, b, cb_arg)> for old style.
 It is possible to obtained the argument associated with a BN_GENCB structure
 (set via a call to BN_GENCB_set or BN_GENCB_set_old) using BN_GENCB_get_arg.
 
-BN_generate_prime (deprecated) works in the same way as
-BN_generate_prime_ex but expects an old style callback function
+BN_generate_prime() (deprecated) works in the same way as
+BN_generate_prime_ex() but expects an old-style callback function
 directly in the B<callback> parameter, and an argument to pass to it in
-the B<cb_arg>. Similarly BN_is_prime and BN_is_prime_fasttest are
-deprecated and can be compared to BN_is_prime_ex and
-BN_is_prime_fasttest_ex respectively.
+the B<cb_arg>. BN_is_prime() and BN_is_prime_fasttest()
+can similarly be compared to BN_is_prime_ex() and
+BN_is_prime_fasttest_ex(), respectively.
 
 =head1 RETURN VALUES