commit cb9226bcdb811c6b30fb4bb2b6b06b378ebf0559 Author: Nick Mathewson <nickm@torproject.org> Date: Tue May 10 21:40:10 2011 -0400 Check for replays in PK-encrypted part of intro cell, not just in the g^x value --- changes/replay-firstpart | 13 +++++++++++++ src/or/rendservice.c | 26 +++++++++++++++++++++++--- 2 files changed, 36 insertions(+), 3 deletions(-) diff --git a/changes/replay-firstpart b/changes/replay-firstpart new file mode 100644 index 0000000..f4a7767 --- /dev/null +++ b/changes/replay-firstpart @@ -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. + diff --git a/src/or/rendservice.c b/src/or/rendservice.c index d1cc7f4..af6737b 100644 --- a/src/or/rendservice.c +++ b/src/or/rendservice.c @@ -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 "