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krb5: Make q param of DH moduli optional

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MSFT makes the `q` field of `DomainParameters` OPTIONAL even though it's
actually required.  We currently validate DH groups not by validating
that p is a Sophie Germain prime but by checking the proposed group
against a compiled-in list and against a krb5.moduli file, therefore we
don't need q.  Besides, for Oakley groups, because p is a Sophie Germain
prime, we'd have q=p/j and j=2, so we can always compute q as needed
(and MIT Kerberos does).
This commit is contained in:
Nicolas Williams
2021-03-24 14:23:13 -05:00
parent 5d939ba1b6
commit cb2064d387
1 changed files with 32 additions and 13 deletions
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25
lib/krb5/pkinit.c
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@@ -473,6 +473,18 @@ build_auth_pack(krb5_context context,
free_DomainParameters(&dp);
return ret;
}
if (dh->q && BN_num_bits(dh->q)) {
/*
* The q parameter is required, but MSFT made it optional.
* It's only required in order to verify the domain parameters
* -- the security of the DH group --, but we validate groups
* against known groups rather than accepting arbitrary groups
* chosen by the peer, so we really don't need to have put it
* on the wire. Because these are Oakley groups, and the
* primes are Sophie Germain primes, q is p>>1 and we can
* compute it on the fly like MIT Kerberos does, but we'd have
* to implement BN_rshift1().
*/
dp.q = calloc(1, sizeof(*dp.q));
if (dp.q == NULL) {
free_DomainParameters(&dp);
@@ -483,6 +495,7 @@ build_auth_pack(krb5_context context,
free_DomainParameters(&dp);
return ret;
}
}
dp.j = NULL;
dp.validationParms = NULL;
@@ -2063,8 +2076,13 @@ _krb5_parse_moduli_line(krb5_context context,
if (ret)
goto out;
ret = parse_integer(context, &p, file, lineno, "q", &m1->q);
if (ret)
goto out;
if (ret) {
m1->q.negative = 0;
m1->q.length = 0;
m1->q.data = 0;
krb5_clear_error_message(context);
ret = 0;
}
*m = m1;
@@ -2245,7 +2263,8 @@ _krb5_dh_group_ok(krb5_context context, unsigned long bits,
for (i = 0; moduli[i] != NULL; i++) {
if (der_heim_integer_cmp(&moduli[i]->g, g) == 0 &&
der_heim_integer_cmp(&moduli[i]->p, p) == 0 &&
(q == NULL || der_heim_integer_cmp(&moduli[i]->q, q) == 0))
(q == NULL || moduli[i]->q.length == 0 ||
der_heim_integer_cmp(&moduli[i]->q, q) == 0))
{
if (bits && bits > moduli[i]->bits) {
krb5_set_error_message(context,