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generate RSA keys of exact length

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This commit is contained in:
Matt Johnston 2014-02-14 23:18:45 +08:00
parent a18a6b8db8
commit 73444f2957
1 changed files with 16 additions and 10 deletions
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26
genrsa.c
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@ -58,12 +58,18 @@ dropbear_rsa_key * gen_rsa_priv_key(unsigned int size) {
exit(1);
}
getrsaprime(key->p, &pminus, key->e, size/16);
getrsaprime(key->q, &qminus, key->e, size/16);
while (1) {
getrsaprime(key->p, &pminus, key->e, size/16);
getrsaprime(key->q, &qminus, key->e, size/16);
if (mp_mul(key->p, key->q, key->n) != MP_OKAY) {
fprintf(stderr, "RSA generation failed\n");
exit(1);
if (mp_mul(key->p, key->q, key->n) != MP_OKAY) {
fprintf(stderr, "RSA generation failed\n");
exit(1);
}
if ((unsigned int)mp_count_bits(key->n) == size) {
break;
}
}
/* lcm(p-1, q-1) */
@ -91,16 +97,16 @@ static void getrsaprime(mp_int* prime, mp_int *primeminus,
unsigned char *buf;
DEF_MP_INT(temp_gcd);
buf = (unsigned char*)m_malloc(size_bytes+1);
buf = (unsigned char*)m_malloc(size_bytes);
m_mp_init(&temp_gcd);
do {
/* generate a random odd number with MSB set, then find the
the next prime above it */
genrandom(buf, size_bytes+1);
buf[0] |= 0x80; /* MSB set */
genrandom(buf, size_bytes);
buf[0] |= 0x80;
bytes_to_mp(prime, buf, size_bytes+1);
bytes_to_mp(prime, buf, size_bytes);
/* find the next integer which is prime, 8 round of miller-rabin */
if (mp_prime_next_prime(prime, 8, 0) != MP_OKAY) {
@ -122,7 +128,7 @@ static void getrsaprime(mp_int* prime, mp_int *primeminus,
/* now we have a good value for result */
mp_clear(&temp_gcd);
m_burn(buf, size_bytes+1);
m_burn(buf, size_bytes);
m_free(buf);
}