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@ -3,6 +3,7 @@ |
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#include <ccan/tal/str/str.h> |
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#include <ccan/time/time.h> |
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#include <common/bolt11.h> |
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#include <common/pseudorand.h> |
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#include <common/type_to_string.h> |
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#include <gossipd/gossip_constants.h> |
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#include <plugins/libplugin.h> |
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@ -47,6 +48,9 @@ struct pay_command { |
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/* Any routehints to use. */ |
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struct route_info **routehints; |
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/* Current node during shadow route calculation. */ |
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const char *shadow; |
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}; |
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static struct command_result *start_pay_attempt(struct command *cmd, |
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@ -354,6 +358,78 @@ static struct command_result *start_pay_attempt(struct command *cmd, |
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dest, amount, cltv, max_hops, pc->riskfactor, exclude); |
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} |
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/* BOLT #7:
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* |
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* If a route is computed by simply routing to the intended recipient and |
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* summing the `cltv_expiry_delta`s, then it's possible for intermediate nodes |
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* to guess their position in the route. Knowing the CLTV of the HTLC, the |
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* surrounding network topology, and the `cltv_expiry_delta`s gives an |
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* attacker a way to guess the intended recipient. Therefore, it's highly |
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* desirable to add a random offset to the CLTV that the intended recipient |
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* will receive, which bumps all CLTVs along the route. |
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* |
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* In order to create a plausible offset, the origin node MAY start a limited |
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* random walk on the graph, starting from the intended recipient and summing |
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* the `cltv_expiry_delta`s, and use the resulting sum as the offset. This |
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* effectively creates a _shadow route extension_ to the actual route and |
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* provides better protection against this attack vector than simply picking a |
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* random offset would. |
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*/ |
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static struct command_result *shadow_route(struct command *cmd, |
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struct pay_command *pc); |
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static struct command_result *add_shadow_route(struct command *cmd, |
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const char *buf, |
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const jsmntok_t *result, |
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struct pay_command *pc) |
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{ |
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/* Use reservoir sampling across the capable channels. */ |
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const jsmntok_t *channels = json_get_member(buf, result, "channels"); |
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const jsmntok_t *chan, *end, *best = NULL; |
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u64 sample; |
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u32 cltv, best_cltv; |
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end = json_next(channels); |
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for (chan = channels + 1; chan < end; chan = json_next(chan)) { |
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u64 sats, v; |
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json_to_u64(buf, json_get_member(buf, chan, "satoshis"), &sats); |
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if (sats * 1000 < pc->msatoshi) |
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continue; |
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/* Don't use if total would exceed 1/4 of our time allowance. */ |
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json_to_number(buf, json_get_member(buf, chan, "delay"), &cltv); |
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if ((pc->final_cltv + cltv) * 4 > pc->maxdelay) |
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continue; |
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v = pseudorand(UINT64_MAX); |
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if (!best || v > sample) { |
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best = chan; |
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best_cltv = cltv; |
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sample = v; |
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} |
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} |
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if (!best) |
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return start_pay_attempt(cmd, pc); |
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pc->final_cltv += best_cltv; |
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pc->shadow = json_strdup(pc, buf, |
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json_get_member(buf, best, "destination")); |
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return shadow_route(cmd, pc); |
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} |
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static struct command_result *shadow_route(struct command *cmd, |
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struct pay_command *pc) |
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{ |
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if (pseudorand(2) == 0) |
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return start_pay_attempt(cmd, pc); |
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return send_outreq(cmd, "listchannels", |
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add_shadow_route, forward_error, pc, |
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"'source' : '%s'", pc->shadow); |
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} |
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/* gossipd doesn't know much about the current state of channels; here we
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* manually exclude peers which are disconnected and channels which lack |
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* current capacity (it will eliminate those without total capacity). */ |
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@ -406,7 +482,7 @@ static struct command_result *listpeers_done(struct command *cmd, |
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} |
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} |
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return start_pay_attempt(cmd, pc); |
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return shadow_route(cmd, pc); |
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} |
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/* Trim route to this length by taking from the *front* of route
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@ -504,6 +580,7 @@ static struct command_result *handle_pay(struct command *cmd, |
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pc->riskfactor = *riskfactor; |
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pc->final_cltv = b11->min_final_cltv_expiry; |
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pc->dest = type_to_string(cmd, struct pubkey, &b11->receiver_id); |
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pc->shadow = tal_strdup(pc, pc->dest); |
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pc->payment_hash = type_to_string(pc, struct sha256, |
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&b11->payment_hash); |
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pc->stoptime = timeabs_add(time_now(), time_from_sec(*retryfor)); |
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Rusty Russell
6 years ago
Christian Decker