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authorKevin B Kenny <kennykb@acm.org>2005-01-19 22:41:26 (GMT)
committerKevin B Kenny <kennykb@acm.org>2005-01-19 22:41:26 (GMT)
commitef78ca64ce6ba6a8786f083318fe536f2bd52925 (patch)
tree47f8ad0d7291237c7f9af988c5e05275ed9286ee /libtommath/bn_mp_prime_random_ex.c
parentb23d942a1e86ddee18c2309afd7fa7e9afa79ef8 (diff)
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Import of libtommath 0.33
Diffstat (limited to 'libtommath/bn_mp_prime_random_ex.c')
-rw-r--r--libtommath/bn_mp_prime_random_ex.c123
1 files changed, 123 insertions, 0 deletions
diff --git a/libtommath/bn_mp_prime_random_ex.c b/libtommath/bn_mp_prime_random_ex.c
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+#include <tommath.h>
+#ifdef BN_MP_PRIME_RANDOM_EX_C
+/* LibTomMath, multiple-precision integer library -- Tom St Denis
+ *
+ * LibTomMath is a library that provides multiple-precision
+ * integer arithmetic as well as number theoretic functionality.
+ *
+ * The library was designed directly after the MPI library by
+ * Michael Fromberger but has been written from scratch with
+ * additional optimizations in place.
+ *
+ * The library is free for all purposes without any express
+ * guarantee it works.
+ *
+ * Tom St Denis, tomstdenis@iahu.ca, http://math.libtomcrypt.org
+ */
+
+/* makes a truly random prime of a given size (bits),
+ *
+ * Flags are as follows:
+ *
+ * LTM_PRIME_BBS - make prime congruent to 3 mod 4
+ * LTM_PRIME_SAFE - make sure (p-1)/2 is prime as well (implies LTM_PRIME_BBS)
+ * LTM_PRIME_2MSB_OFF - make the 2nd highest bit zero
+ * LTM_PRIME_2MSB_ON - make the 2nd highest bit one
+ *
+ * You have to supply a callback which fills in a buffer with random bytes. "dat" is a parameter you can
+ * have passed to the callback (e.g. a state or something). This function doesn't use "dat" itself
+ * so it can be NULL
+ *
+ */
+
+/* This is possibly the mother of all prime generation functions, muahahahahaha! */
+int mp_prime_random_ex(mp_int *a, int t, int size, int flags, ltm_prime_callback cb, void *dat)
+{
+ unsigned char *tmp, maskAND, maskOR_msb, maskOR_lsb;
+ int res, err, bsize, maskOR_msb_offset;
+
+ /* sanity check the input */
+ if (size <= 1 || t <= 0) {
+ return MP_VAL;
+ }
+
+ /* LTM_PRIME_SAFE implies LTM_PRIME_BBS */
+ if (flags & LTM_PRIME_SAFE) {
+ flags |= LTM_PRIME_BBS;
+ }
+
+ /* calc the byte size */
+ bsize = (size>>3) + ((size&7)?1:0);
+
+ /* we need a buffer of bsize bytes */
+ tmp = OPT_CAST(unsigned char) XMALLOC(bsize);
+ if (tmp == NULL) {
+ return MP_MEM;
+ }
+
+ /* calc the maskAND value for the MSbyte*/
+ maskAND = ((size&7) == 0) ? 0xFF : (0xFF >> (8 - (size & 7)));
+
+ /* calc the maskOR_msb */
+ maskOR_msb = 0;
+ maskOR_msb_offset = (size - 2) >> 3;
+ if (flags & LTM_PRIME_2MSB_ON) {
+ maskOR_msb |= 1 << ((size - 2) & 7);
+ } else if (flags & LTM_PRIME_2MSB_OFF) {
+ maskAND &= ~(1 << ((size - 2) & 7));
+ }
+
+ /* get the maskOR_lsb */
+ maskOR_lsb = 0;
+ if (flags & LTM_PRIME_BBS) {
+ maskOR_lsb |= 3;
+ }
+
+ do {
+ /* read the bytes */
+ if (cb(tmp, bsize, dat) != bsize) {
+ err = MP_VAL;
+ goto error;
+ }
+
+ /* work over the MSbyte */
+ tmp[0] &= maskAND;
+ tmp[0] |= 1 << ((size - 1) & 7);
+
+ /* mix in the maskORs */
+ tmp[maskOR_msb_offset] |= maskOR_msb;
+ tmp[bsize-1] |= maskOR_lsb;
+
+ /* read it in */
+ if ((err = mp_read_unsigned_bin(a, tmp, bsize)) != MP_OKAY) { goto error; }
+
+ /* is it prime? */
+ if ((err = mp_prime_is_prime(a, t, &res)) != MP_OKAY) { goto error; }
+ if (res == MP_NO) {
+ continue;
+ }
+
+ if (flags & LTM_PRIME_SAFE) {
+ /* see if (a-1)/2 is prime */
+ if ((err = mp_sub_d(a, 1, a)) != MP_OKAY) { goto error; }
+ if ((err = mp_div_2(a, a)) != MP_OKAY) { goto error; }
+
+ /* is it prime? */
+ if ((err = mp_prime_is_prime(a, t, &res)) != MP_OKAY) { goto error; }
+ }
+ } while (res == MP_NO);
+
+ if (flags & LTM_PRIME_SAFE) {
+ /* restore a to the original value */
+ if ((err = mp_mul_2(a, a)) != MP_OKAY) { goto error; }
+ if ((err = mp_add_d(a, 1, a)) != MP_OKAY) { goto error; }
+ }
+
+ err = MP_OKAY;
+error:
+ XFREE(tmp);
+ return err;
+}
+
+
+#endif