79 lines
1.6 KiB
C
79 lines
1.6 KiB
C
#include "mycrypt.h"
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#ifdef MPI
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#define UPPER_LIMIT PRIME_SIZE
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/* figures out if a number is prime (MR test) */
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int is_prime(mp_int *N, int *result)
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{
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int err;
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if ((err = mp_prime_is_prime(N, 8, result)) != MP_OKAY) {
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return CRYPT_MEM;
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}
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return CRYPT_OK;
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}
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int rand_prime(mp_int *N, long len, prng_state *prng, int wprng)
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{
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unsigned char buf[260];
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int err, step, ormask;
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_ARGCHK(N != NULL);
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/* pass a negative size if you want a prime congruent to 3 mod 4 */
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if (len < 0) {
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step = 1;
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ormask = 3;
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len = -len;
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} else {
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step = 0;
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ormask = 1;
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}
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/* allow sizes between 2 and 256 bytes for a prime size */
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if (len < 2 || len > 256) {
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return CRYPT_INVALID_PRIME_SIZE;
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}
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/* valid PRNG? */
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if ((err = prng_is_valid(wprng)) != CRYPT_OK) {
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return err;
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}
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/* read the prng */
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if (prng_descriptor[wprng].read(buf+2, (unsigned long)len, prng) != (unsigned long)len) {
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return CRYPT_ERROR_READPRNG;
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}
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/* set sign byte to zero */
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buf[0] = (unsigned char)0;
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/* Set the top byte to 0x01 which makes the number a len*8 bit number */
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buf[1] = (unsigned char)0x01;
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/* set the LSB to the desired settings
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* (1 for any prime, 3 for primes congruent to 3 mod 4)
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*/
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buf[len+1] |= (unsigned char)ormask;
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/* read the number in */
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if (mp_read_raw(N, buf, 2+len) != MP_OKAY) {
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return CRYPT_MEM;
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}
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/* Find the next prime after N */
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if (mp_prime_next_prime(N, 8, step) != MP_OKAY) {
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return CRYPT_MEM;
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}
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#ifdef CLEAN_STACK
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zeromem(buf, sizeof(buf));
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#endif
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return CRYPT_OK;
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}
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#endif
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