From 73444f2957f15e808d1c5d0547a1b4993dc2f160 Mon Sep 17 00:00:00 2001 From: Matt Johnston 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 cdc585d..dfd81b3 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); }