a

libsec/genprime.c

@@ -0,0 +1,27 @@
+#include "os.h"
+#include <mp.h>
+#include <libsec.h>
+
+//  generate a probable prime.  accuracy is the miller-rabin interations
+void
+genprime(mpint *p, int n, int accuracy)
+{
+	mpdigit x;
+
+	// generate n random bits with high and low bits set
+	mpbits(p, n);
+	genrandom((uchar*)p->p, (n+7)/8);
+	p->top = (n+Dbits-1)/Dbits;
+	x = 1;
+	x <<= ((n-1)%Dbits);
+	p->p[p->top-1] &= (x-1);
+	p->p[p->top-1] |= x;
+	p->p[0] |= 1;
+
+	// keep icrementing till it looks prime
+	for(;;){
+		if(probably_prime(p, accuracy))
+			break;
+		mpadd(p, mptwo, p);
+	}
+}