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common/blindedpath: EXPERIMENTAL creation of blinded paths.

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For inclusion in the onion as a reply path.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
This commit is contained in:
Rusty Russell 2020-12-09 14:27:50 +10:30
parent 1d1804e318
commit f315f1c63f
3 changed files with 119 additions and 0 deletions
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1
common/Makefile
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@ -83,6 +83,7 @@ COMMON_SRC_NOGEN := \
ifeq ($(EXPERIMENTAL_FEATURES),1)
COMMON_SRC_NOGEN += common/psbt_internal.c
COMMON_SRC_NOGEN += common/blindedpath.c
endif
COMMON_SRC_GEN := common/status_wiregen.c common/peer_status_wiregen.c

101
common/blindedpath.c Normal file
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@ -0,0 +1,101 @@
#include <bitcoin/privkey.h>
#include <bitcoin/pubkey.h>
#include <ccan/cast/cast.h>
#include <common/blindedpath.h>
#include <common/blinding.h>
#include <common/bolt11.h>
#include <common/hmac.h>
#include <common/node_id.h>
#include <common/utils.h>
#include <secp256k1_ecdh.h>
#include <sodium.h>
#include <wire/onion_wire.h>
/* FIXME: Pad with dummy nodes, but make sure to check them on recv! */
struct onionmsg_path **make_blindedpath(const tal_t *ctx,
const struct pubkey *route,
struct pubkey *initial_blinding,
struct pubkey *final_blinding)
{
struct privkey e;
struct pubkey *pk_e, *b;
struct secret *rho;
struct onionmsg_path **path;
size_t num = tal_count(route);
if (!num)
abort();
/* E(i) */
pk_e = tal_arr(tmpctx, struct pubkey, num);
/* B(i) */
b = tal_arr(tmpctx, struct pubkey, num);
/* rho(i) */
rho = tal_arr(tmpctx, struct secret, num);
randombytes_buf(&e, sizeof(e));
if (!pubkey_from_privkey(&e, &pk_e[0]))
abort();
for (size_t i = 0; i < num; i++) {
struct secret ss;
struct secret hmac;
struct sha256 h;
if (secp256k1_ecdh(secp256k1_ctx, ss.data,
&route[i].pubkey, e.secret.data,
NULL, NULL) != 1)
abort();
subkey_from_hmac("blinded_node_id", &ss, &hmac);
b[i] = route[i];
if (i != 0) {
if (secp256k1_ec_pubkey_tweak_mul(secp256k1_ctx,
&b[i].pubkey, hmac.data) != 1)
abort();
}
subkey_from_hmac("rho", &ss, &rho[i]);
blinding_hash_e_and_ss(&pk_e[i], &ss, &h);
if (i != num-1)
blinding_next_pubkey(&pk_e[i], &h, &pk_e[i+1]);
blinding_next_privkey(&e, &h, &e);
}
*initial_blinding = pk_e[0];
*final_blinding = pk_e[num-1];
path = tal_arr(ctx, struct onionmsg_path *, num);
for (size_t i = 0; i < num; i++) {
path[i] = tal(path, struct onionmsg_path);
path[i]->node_id = b[i];
}
for (size_t i = 0; i < num - 1; i++) {
const unsigned char npub[crypto_aead_chacha20poly1305_ietf_NPUBBYTES] = { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 };
struct tlv_onionmsg_payload *inner;
int ret;
/* Inner is encrypted */
inner = tlv_onionmsg_payload_new(tmpctx);
/* FIXME: We could support scids, too */
inner->next_node_id = cast_const(struct pubkey *, &route[i+1]);
path[i]->enctlv = tal_arr(path, u8, 0);
towire_encmsg_tlvs(&path[i]->enctlv, inner);
towire_pad(&path[i]->enctlv,
crypto_aead_chacha20poly1305_ietf_ABYTES);
ret = crypto_aead_chacha20poly1305_ietf_encrypt(path[i]->enctlv, NULL,
path[i]->enctlv,
tal_bytelen(path[i]->enctlv) - crypto_aead_chacha20poly1305_ietf_ABYTES,
NULL, 0,
NULL, npub,
rho[i].data);
assert(ret == 0);
}
/* Final one has no enctlv */
path[num-1]->enctlv = NULL;
return path;
}

17
common/blindedpath.h Normal file
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@ -0,0 +1,17 @@
#ifndef LIGHTNING_COMMON_BLINDEDPATH_H
#define LIGHTNING_COMMON_BLINDEDPATH_H
#include "config.h"
#include <ccan/tal/tal.h>
#if EXPERIMENTAL_FEATURES
struct route_info;
struct pubkey;
/* Fills in *initial_blinding and *final_blinding and returns
* onionmsg_path array for this route */
struct onionmsg_path **make_blindedpath(const tal_t *ctx,
const struct pubkey *route,
struct pubkey *initial_blinding,
struct pubkey *final_blinding);
#endif /* EXPERIMENTAL_FEATURES */
#endif /* LIGHTNING_COMMON_BLINDEDPATH_H */