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lightningd: Base peer->seed off of the channel ID

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The peer->seed needs to be unique for each channel, since bitcoin
pubkeys and the shachain are generated from it. However we also need
to guarantee that the same seed is generated for a given channel every
time, e.g., upon a restart. The DB channel ID is guaranteed to be
unique, and will not change throughout the lifetime of a channel, so
we simply mix it in, instead of a separate increasing counter.

We also needed to make sure to store in the DB before deriving the
seed, in order to get an ID assigned by the DB.

Signed-off-by: Christian Decker <decker.christian@gmail.com>
This commit is contained in:
Christian Decker
2017-08-21 11:25:15 +02:00
committed by Rusty Russell
parent e51d261f51
commit def3d77a70
4 changed files with 40 additions and 13 deletions
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12
lightningd/lightningd.c
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@@ -178,21 +178,17 @@ static const char *find_my_path(const tal_t *ctx, const char *argv0)
}
void derive_peer_seed(struct lightningd *ld, struct privkey *peer_seed,
const struct pubkey *peer_id)
const struct pubkey *peer_id, const u64 channel_id)
{
be64 counter = cpu_to_be64(ld->peer_counter);
u8 input[PUBKEY_DER_LEN + sizeof(counter)];
u8 input[PUBKEY_DER_LEN + sizeof(channel_id)];
char *info = "per-peer seed";
pubkey_to_der(input, peer_id);
memcpy(input + PUBKEY_DER_LEN, &counter, sizeof(counter));
memcpy(input + PUBKEY_DER_LEN, &channel_id, sizeof(channel_id));
hkdf_sha256(peer_seed, sizeof(*peer_seed),
input, sizeof(input),
&ld->peer_seed, sizeof(ld->peer_seed),
info, strlen(info));
/* FIXME: This must be saved in db. */
ld->peer_counter++;
}
static void shutdown_subdaemons(struct lightningd *ld)
@@ -273,7 +269,7 @@ int main(int argc, char *argv[])
list_for_each(&ld->peers, peer, list) {
populate_peer(ld, peer);
peer->seed = tal(peer, struct privkey);
derive_peer_seed(ld, peer->seed, &peer->id);
derive_peer_seed(ld, peer->seed, &peer->id, peer->channel->id);
}
/* Create RPC socket (if any) */