The scheme implemented is described below, and largely follows the paper
"SwiftEC: Shallue–van de Woestijne Indifferentiable Function To Elliptic Curves",
by Chavez-Saab, Rodriguez-Henriquez, and Tibouchi
(https://eprint.iacr.org/2022/759).
A new 64-byte public key format is introduced, with the property that *every*
64-byte array is an encoding for a non-infinite curve point. Each curve point
has roughly 2^256 distinct encodings. This permits disguising public keys as
uniformly random bytes.
The new API functions:
* secp256k1_ellswift_encode: convert a normal public key to an ellswift 64-byte
public key, using additional entropy to pick among the many possible
encodings.
* secp256k1_ellswift_decode: convert an ellswift 64-byte public key to a normal
public key.
* secp256k1_ellswift_create: a faster and safer equivalent to calling
secp256k1_ec_pubkey_create + secp256k1_ellswift_encode.
* secp256k1_ellswift_xdh: x-only ECDH directly on ellswift 64-byte public keys,
where the key encodings are fed to the hash function.
The scheme itself is documented in secp256k1_ellswift.h.
f3126fdfec7c4dbfab3acf01714325b027110aff norm arg: remove prove edge tests which are now covered by vectors (Jonas Nick)
847ed9ecb2233f1e233fae1791b5adcdeb3be52b norm arg: add verification to prove vectors (Jonas Nick)
cf797ed2a4ccc7422de2f4081a6d6bcf536d72c8 norm arg: add prove test vectors (Jonas Nick)
095c1e749c106285e8252d6490073974dd4d8fcc norm arg: add prove_const to tests (Jonas Nick)
bf7bf8a64fa7a7256ad64f75ae0bcb9fccbd0ea4 norm arg: split norm_arg_zero into prove_edge and verify_zero_len (Jonas Nick)
a70c4d4a8a6970f8e299de541cc75f2fc2e39e76 norm arg: add test vector for |n| = 0 (Jonas Nick)
f5e4b16f0f96ae871d221900673f426e9c9ce85e norm arg: add test vector for sign bit malleability (Jonas Nick)
c0de361fc53dbfb0b058895f4824eba4d423e191 norm arg: allow X and R to be the point at infinity (Jonas Nick)
f22834f20252f9ca3e17f36093940e2aa2735790 norm arg: add verify vector for n = [0], l = [0] (Jonas Nick)
d8e7f3763bac9e52d07643a01c8352cadded64d2 musig: move ge_{serialize,parse}_ext to module-independent file (Jonas Nick)
Pull request description:
ACKs for top commit:
Liam-Eagen:
ACK f3126fd
Tree-SHA512: 1aad86521fce74435beabe7690c7fcc38ad9ae7a884ddcab69ef825b573433f700723a7672d29df1b4465bc33d5957b6a46f657f988cfd2cc73fa94a3472357d
8e142ca4102ade1b90dcb06d6c78405ef3220599 Move `SECP256K1_INLINE` macro definition out from `include/secp256k1.h` (Hennadii Stepanov)
77445898a5852ecd38ab95cfb329333a82673115 Remove `SECP256K1_INLINE` usage from examples (Hennadii Stepanov)
Pull request description:
From [IRC](https://gnusha.org/secp256k1/2023-01-31.log):
> 06:29 \< hebasto\> What are reasons to define the `SECP256K1_INLINE` macro in user's `include/secp256k1.h` header, while it is used internally only?
> 06:32 \< hebasto\> I mean, any other (or a new dedicated) header in `src` looks more appropriate, no?
> 06:35 \< sipa\> I think it may just predate any "utility" internal headers.
> 06:42 \< sipa\> I think it makes sense to move it to util.h
Pros:
- it is a step in direction to better organized headers (in context of #924, #1039)
Cons:
- code duplication for `SECP256K1_GNUC_PREREQ` macro
ACKs for top commit:
sipa:
utACK 8e142ca4102ade1b90dcb06d6c78405ef3220599
real-or-random:
utACK 8e142ca410
Tree-SHA512: 180e0ba7c2ef242b765f20698b67d06c492b7b70866c21db27c18d8b2e85c3e11f86c6cb99ffa88bbd23891ce3ee8a24bc528f2c91167ec2fddc167463f78eac
b43dd83b43eac0ca8ad9ee1f557e9126c9e08d9e musig: add missing static keyword to function (Jonas Nick)
068e6a036a953e48bc90f9a96b318e350f474a3a musig: add test vectors from BIP MuSig (Jonas Nick)
36621d13bedf44eeedd2a1773e30e849972e5bff musig: update to BIP v1.0.0-rc.2 "Add ''pk'' arg to ''NonceGen''" (Jonas Nick)
d717a4980bc3e2e36bd32a02466226ef49a5d625 musig: update to BIP v0.8 "Switch from X-only to plain pk inputs." (Jonas Nick)
304f1bc96d6bdb5c1b5b1b9a321eac8f9a27fde4 extrakeys: add pubkey_sort test vectors from BIP MuSig2 (Jonas Nick)
ae89051547435cab5042a13d85562def9cabdd61 extrakeys: replace xonly_sort with pubkey_sort (Jonas Nick)
98242fcdd9519d0d5a349b0344aeea0ab4e796e9 extrakeys: add secp256k1_pubkey_cmp (Jonas Nick)
73d5b6654d472eb0cebbffd5a934caf174d29307 musig: update to BIP v0.7.0 (NonceGen) (Jonas Nick)
060887e9d749062242b4de3935b27fdcb0802c87 musig: update to BIP v0.5.1 "Rename ordinary tweaking to plain" (Jonas Nick)
cbe2815633411479e8305deb8b69bce94df723af musig: update to BIP v0.4 "Allow the output of NonceAgg to be inf" (Jonas Nick)
206017d67d9bb8b21d5cc924ba53e1618274774c musig: update to BIP v0.3 (NonceGen) (Jonas Nick)
d800dd55db28a710bb510a2a5fc33519d355a91c musig: remove test vectors (Jonas Nick)
Pull request description:
Version 1.0.0-rc.3 of BIP MuSig2 can be found [here](https://github.com/jonasnick/bips/pull/75). This PR does _not_ implement the following optional features that have been added to BIP MuSig2:
- variable length messages
- deterministic signing
- identifiable aborts
The PR also does _not_ yet change the `secnonce` structure to also contain the signer's public key (which would also imply changing the seckey argument in `sign` to a keypair). Additionally, we may want to rename some things in the future to be more consistent with the BIP (e.g. keyagg_cache vs. keyagg_ctx, applytweak vs. tweak_add).
ACKs for top commit:
ariard:
Light Code Review ACK b43dd83b, mostly looks on how the user API will make sense for Lightning, thanks for the answers!
real-or-random:
ACK b43dd83b43eac0ca8ad9ee1f557e9126c9e08d9e
Tree-SHA512: 9b1410951b55a1b0e6590b8c302052996d1fb6d9771765498b4282ff68b44ab0d6add8144c9330217b682ec5a93508b5546099db9a1f2c865f99253010dd76f4
- 0.7.0: Change ''NonceGen'' such that output when message is not present is different from when message is present but has length 0.
- 0.6.0: Change order of arguments and serialization of the message in the ''NonceGen'' hash function
