From 73444f2957f15e808d1c5d0547a1b4993dc2f160 Mon Sep 17 00:00:00 2001
From: Matt Johnston <matt@ucc.asn.au>
Date: Fri, 14 Feb 2014 23:18:45 +0800
Subject: [PATCH] generate RSA keys of exact length
---
genrsa.c | 26 ++++++++++++++++----------
1 file changed, 16 insertions(+), 10 deletions(-)
diff --git a/genrsa.c b/genrsa.c
index cdc585db..dfd81b3a 100644
--- a/genrsa.c
+++ b/genrsa.c
@@ -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);
}
--
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