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implement smaller private key sizes

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This commit is contained in:
Steffen Jaeckel 2017-06-09 18:07:44 +02:00
parent f46b32ba2e
commit f31d8ff864
1 changed files with 50 additions and 5 deletions
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55
src/pk/dh/dh.c
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@ -116,6 +116,39 @@ int dh_make_key(prng_state *prng, int wprng, int keysize, dh_key *key)
unsigned long x;
void *p, *g;
int err;
/* Table of the strength estimates from https://tools.ietf.org/html/rfc3526#section-8
* We use them as a reference to estimate an appropriate private key size.
*/
const int private_key_sizes[][2] =
{
#ifdef LTC_DH768
{ 180, 240, },
#endif
#ifdef LTC_DH1024
{ 180, 240, },
#endif
#ifdef LTC_DH1536
{ 180, 240, },
#endif
#ifdef LTC_DH2048
/* here we use 224 instead of 220 as NIST requires
* at least 224bits for the 2048bit group */
{ 224, 320, },
#endif
#ifdef LTC_DH3072
{ 260, 420, },
#endif
#ifdef LTC_DH4096
{ 300, 480, },
#endif
#ifdef LTC_DH6144
{ 340, 540, },
#endif
#ifdef LTC_DH8192
{ 380, 620, },
#endif
{ INT_MAX, INT_MAX, }
};
LTC_ARGCHK(key != NULL);
@ -126,16 +159,28 @@ int dh_make_key(prng_state *prng, int wprng, int keysize, dh_key *key)
/* find key size */
for (x = 0; (keysize > sets[x].size) && (sets[x].size != 0); x++);
#ifdef FAST_PK
keysize = MIN(sets[x].size, 32);
#else
keysize = sets[x].size;
#endif
if (sets[x].size == 0) {
return CRYPT_INVALID_KEYSIZE;
}
if (x >= sizeof(private_key_sizes) / sizeof(private_key_sizes[0])) {
return CRYPT_INVALID_KEYSIZE;
}
key->idx = x;
/* 1. Read a random digit
* 2. Shorten it to the range between both strengths'
* 3. Now we have a random digit between both strengths'
* 4. Make sure the division afterwards rounds up
* 5. Convert bit to byte
*/
if (prng_descriptor[wprng].read((void*)&keysize, sizeof(keysize), prng) != sizeof(keysize)) {
return CRYPT_ERROR_READPRNG;
}
keysize %= private_key_sizes[x][1] - private_key_sizes[x][0];
keysize += private_key_sizes[x][0];
keysize += 7;
keysize /= 8;
/* allocate buffer */
buf = XMALLOC(keysize);
if (buf == NULL) {