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lightningd/derive_basepoints: helper to increment our per_commit_point.

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Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
This commit is contained in:
Rusty Russell 2017-04-01 21:28:30 +10:30
parent 8f2c4348a9
commit dd15361935
2 changed files with 41 additions and 0 deletions
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35
lightningd/derive_basepoints.c
View file

@ -1,3 +1,4 @@
#include <assert.h>
#include <ccan/crypto/hkdf_sha256/hkdf_sha256.h>
#include <ccan/crypto/sha256/sha256.h>
#include <ccan/crypto/shachain/shachain.h>
@ -59,3 +60,37 @@ bool derive_basepoints(const struct privkey *seed,
return true;
}
bool next_per_commit_point(const struct sha256 *shaseed,
struct sha256 *old_commit_secret,
struct pubkey *per_commit_point,
u64 per_commit_index)
{
struct sha256 per_commit_secret;
/* Get old secret. */
if (per_commit_index > 0)
shachain_from_seed(shaseed, 281474976710655ULL
- (per_commit_index - 1),
old_commit_secret);
else
assert(old_commit_secret == NULL);
/* Derive new per-commitment-point. */
shachain_from_seed(shaseed, 281474976710655ULL - (per_commit_index + 1),
&per_commit_secret);
/* BOLT #3:
*
* The `per-commitment-point` is generated using EC multiplication:
*
* per-commitment-point = per-commitment-secret * G
*/
if (secp256k1_ec_pubkey_create(secp256k1_ctx,
&per_commit_point->pubkey,
per_commit_secret.u.u8) != 1)
return false;
return true;
}

6
lightningd/derive_basepoints.h
View file

@ -27,4 +27,10 @@ bool derive_basepoints(const struct privkey *seed,
struct pubkey *per_commit_point,
u64 per_commit_index);
/* Give up secret for index-1, and generate per-commitment point for N+1. */
bool next_per_commit_point(const struct sha256 *shaseed,
struct sha256 *old_commit_secret,
struct pubkey *per_commit_point,
u64 per_commit_index);
#endif /* LIGHTNING_LIGHTNINGD_DERIVE_BASEPOINTS_H */