X-Git-Url: https://git.distorted.org.uk/u/mdw/catacomb/blobdiff_plain/2b2d07ca33cf57a82d416ee0aafa5842bf24e509..052b36d05a622a93733b735acce2de865b14627b:/strongprime.c

diff --git a/strongprime.c b/strongprime.c
index 4a7ddb8..a5f6052 100644
--- a/strongprime.c
+++ b/strongprime.c
@@ -1,6 +1,6 @@
 /* -*-c-*-
  *
- * $Id: strongprime.c,v 1.1 1999/12/22 15:51:22 mdw Exp $
+ * $Id: strongprime.c,v 1.2 2000/02/12 18:21:03 mdw Exp $
  *
  * Generate `strong' prime numbers
  *
@@ -30,6 +30,9 @@
 /*----- Revision history --------------------------------------------------* 
  *
  * $Log: strongprime.c,v $
+ * Revision 1.2  2000/02/12 18:21:03  mdw
+ * Overhaul of key management (again).
+ *
  * Revision 1.1  1999/12/22 15:51:22  mdw
  * Find `strong' RSA primes using Gordon's algorithm.
  *
@@ -50,37 +53,34 @@
 
 /*----- Main code ---------------------------------------------------------*/
 
-/* --- @strongprime@ --- *
+/* --- @strongprime_setup@ --- *
  *
  * Arguments:	@const char *name@ = pointer to name root
- *		@mp *d@ = destination integer
+ *		@mp *d@ = destination for search start point
+ *		@pfilt *f@ = where to store filter jump context
  *		@unsigned nbits@ = number of bits wanted
  *		@grand *r@ = random number source
  *		@unsigned n@ = number of attempts to make
  *		@pgen_proc *event@ = event handler function
  *		@void *ectx@ = argument for the event handler
  *
- * Returns:	A `strong' prime, or zero.
- *
- * Use:		Finds `strong' primes.  A strong prime %$p$% is such that
- *
- *		  * %$p - 1$% has a large prime factor %$r$%,
- *		  * %$p + 1$% has a large prime factor %$s$%, and
- *		  * %$r - 1$% has a large prime factor %$t$%.
+ * Returns:	A starting point for a `strong' prime search, or zero.
  *
- *		The numbers produced may be slightly larger than requested,
- *		by a few bits.
+ * Use:		Sets up for a strong prime search, so that primes with
+ *		particular properties can be found.  It's probably important
+ *		to note that the number left in the filter context @f@ is
+ *		congruent to 2 (mod 4).
  */
 
-mp *strongprime(const char *name, mp *d, unsigned nbits, grand *r,
-		unsigned n, pgen_proc *event, void *ectx)
+mp *strongprime_setup(const char *name, mp *d, pfilt *f, unsigned nbits,
+		      grand *r, unsigned n, pgen_proc *event, void *ectx)
 {
-  mp *s, *t, *q, *p = 0;
+  mp *s, *t, *q;
   dstr dn = DSTR_INIT;
 
-  mp *rr = MP_NEW;
+  mp *rr = d;
   pgen_filterctx c;
-  pgen_jumpctx cj;
+  pgen_jumpctx j;
   rabin rb;
 
   /* --- The bitslop parameter --- *
@@ -91,7 +91,7 @@ mp *strongprime(const char *name, mp *d, unsigned nbits, grand *r,
    * numbers around 10 seem to be good.
    */
 
-#define BITSLOP 10
+#define BITSLOP 12
 
   /* --- Choose two primes %$s$% and %$t$% of half the required size --- */
 
@@ -101,7 +101,7 @@ mp *strongprime(const char *name, mp *d, unsigned nbits, grand *r,
   rr = mprand(rr, nbits, r, 1);
   DRESET(&dn); dstr_putf(&dn, "%s [s]", name);
   if ((s = pgen(dn.buf, MP_NEW, rr, event, ectx, n, pgen_filter, &c,
-		rabin_iters(nbits), pgen_test, &rb)) == 0)
+	   rabin_iters(nbits), pgen_test, &rb)) == 0)
     goto fail_s;
   mp_burn(s);
 
@@ -119,12 +119,13 @@ mp *strongprime(const char *name, mp *d, unsigned nbits, grand *r,
   rr = mp_lsl(rr, rr, BITSLOP - 1);
   rr = mp_add(rr, rr, MP_ONE);
   DRESET(&dn); dstr_putf(&dn, "%s [r]", name);
-  cj.j = &c.f;
+  j.j = &c.f;
   nbits += BITSLOP;
-  if ((q = pgen(dn.buf, MP_NEW, rr, event, ectx, n, pgen_jump, &cj,
-		rabin_iters(nbits), pgen_test, &rb)) == 0)
-    goto fail_r;
+  q = pgen(dn.buf, MP_NEW, rr, event, ectx, n, pgen_jump, &j,
+	   rabin_iters(nbits), pgen_test, &rb);
   pfilt_destroy(&c.f);
+  if (!q)
+    goto fail_r;
 
   /* --- Select a suitable starting-point for finding %$p$% --- *
    *
@@ -149,32 +150,75 @@ mp *strongprime(const char *name, mp *d, unsigned nbits, grand *r,
     mp *x;
     x = mp_mul(MP_NEW, q, s);
     x = mp_lsl(x, x, 1);
-    pfilt_create(&c.f, x);
+    pfilt_create(f, x);
     x = mp_lsl(x, x, BITSLOP - 1);
     rr = mp_add(rr, rr, x);
     mp_drop(x);
   }
 
-  if ((p = pgen(name, d, rr, event, ectx, n, pgen_jump, &cj,
-		rabin_iters(nbits * 2), pgen_test, &rb)) == 0)
-    goto fail_p;
+  /* --- Return the result --- */
 
-  /* --- Tidy up because we've finished --- */
+#if 0
+fputs("r = ", stdout); mp_writefile(q, stdout, 10); putchar('\n');
+fputs("s = ", stdout); mp_writefile(s, stdout, 10); putchar('\n');
+fputs("t = ", stdout); mp_writefile(t, stdout, 10); putchar('\n');
+#endif
 
-fail_p:
   mp_drop(q);
+  mp_drop(t);
+  mp_drop(s);
+  dstr_destroy(&dn);
+  return (rr);
+
+  /* --- Tidy up if something failed --- */
+
 fail_r:
-  pfilt_destroy(&c.f);
   mp_drop(t);
 fail_t:
   mp_drop(s);
 fail_s:
   mp_drop(rr);
   dstr_destroy(&dn);
-
-  return (p);
+  return (0);
 
 #undef BITSLOP
 }
 
+/* --- @strongprime@ --- *
+ *
+ * Arguments:	@const char *name@ = pointer to name root
+ *		@mp *d@ = destination integer
+ *		@unsigned nbits@ = number of bits wanted
+ *		@grand *r@ = random number source
+ *		@unsigned n@ = number of attempts to make
+ *		@pgen_proc *event@ = event handler function
+ *		@void *ectx@ = argument for the event handler
+ *
+ * Returns:	A `strong' prime, or zero.
+ *
+ * Use:		Finds `strong' primes.  A strong prime %$p$% is such that
+ *
+ *		  * %$p - 1$% has a large prime factor %$r$%,
+ *		  * %$p + 1$% has a large prime factor %$s$%, and
+ *		  * %$r - 1$% has a large prime factor %$t$%.
+ *
+ *		The numbers produced may be slightly larger than requested,
+ *		by a few bits.
+ */
+
+mp *strongprime(const char *name, mp *d, unsigned nbits, grand *r,
+		unsigned n, pgen_proc *event, void *ectx)
+{
+  pfilt f;
+  pgen_jumpctx j;
+  rabin rb;
+  
+  d = strongprime_setup(name, d, &f, nbits, r, n, event, ectx);
+  j.j = &f;
+  d = pgen(name, d, d, event, ectx, n, pgen_jump, &j,
+	   rabin_iters(nbits), pgen_test, &rb);
+  pfilt_destroy(&f);
+  return (d);
+}
+
 /*----- That's all, folks -------------------------------------------------*/