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Check for replays in PK-encrypted part of intro cell, not just in the g^x value

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This commit is contained in:
Nick Mathewson 2011-05-10 21:40:10 -04:00
parent c75ee94ab4
commit cb9226bcdb
2 changed files with 36 additions and 3 deletions
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13
changes/replay-firstpart Normal file
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@ -0,0 +1,13 @@
o Minor features (security):
- Check for replays of the public-key encrypted portion of an
INTRODUCE1 cell, in addition to the current check for replays of
the g^x value. This prevents a possible class of active attacks
by an attacker who controls both an introduction point and a
rendezvous point, and who uses the malleability of AES-CTR to
alter the encrypted g^x portion of the INTRODUCE1 cell. We
think that these attacks is infeasible (requiring the attacker
to send on the order of zettabytes of altered cells in a short
interval), but we'd rather block them off in case there are any
classes of this attack that we missed. Reported by dvorak.

26
src/or/rendservice.c
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@ -976,6 +976,29 @@ rend_service_introduce(origin_circuit_t *circuit, const uint8_t *request,
"PK-encrypted portion of INTRODUCE2 cell was truncated.");
return -1;
}
if (!service->accepted_intros)
service->accepted_intros = digestmap_new();
{
char pkpart_digest[DIGEST_LEN];
/* Check for replay of PK-encrypted portion. It is slightly naughty to
use the same digestmap to check for this and for g^x replays, but
collisions are tremendously unlikely.
*/
crypto_digest(pkpart_digest, (char*)request+DIGEST_LEN, keylen);
access_time = digestmap_get(service->accepted_intros, pkpart_digest);
if (access_time != NULL) {
log_warn(LD_REND, "Possible replay detected! We received an "
"INTRODUCE2 cell with same PK-encrypted part %d seconds ago. "
"Dropping cell.", (int)(now-*access_time));
return -1;
}
access_time = tor_malloc(sizeof(time_t));
*access_time = now;
digestmap_set(service->accepted_intros, pkpart_digest, access_time);
}
/* Next N bytes is encrypted with service key */
note_crypto_pk_op(REND_SERVER);
r = crypto_pk_private_hybrid_decrypt(
@ -1109,9 +1132,6 @@ rend_service_introduce(origin_circuit_t *circuit, const uint8_t *request,
/* Check whether there is a past request with the same Diffie-Hellman,
* part 1. */
if (!service->accepted_intros)
service->accepted_intros = digestmap_new();
access_time = digestmap_get(service->accepted_intros, diffie_hellman_hash);
if (access_time != NULL) {
log_warn(LD_REND, "Possible replay detected! We received an "