-
Notifications
You must be signed in to change notification settings - Fork 1k
Commit
This commit does not belong to any branch on this repository, and may belong to a fork outside of the repository.
Add module "musig" that implements MuSig2 multi-signatures (BIP 327)
- Loading branch information
Showing
22 changed files
with
4,302 additions
and
14 deletions.
There are no files selected for viewing
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,51 @@ | ||
| Notes on the musig module API | ||
| =========================== | ||
|
|
||
| The following sections contain additional notes on the API of the musig module (`include/secp256k1_musig.h`). | ||
| A usage example can be found in `examples/musig.c`. | ||
|
|
||
| ## API misuse | ||
|
|
||
| The musig API is designed to be as misuse resistant as possible. | ||
| However, the MuSig protocol has some additional failure modes (mainly due to interactivity) that do not appear in single-signing. | ||
| While the results can be catastrophic (e.g. leaking of the secret key), it is unfortunately not possible for the musig implementation to rule out all such failure modes. | ||
|
|
||
| Therefore, users of the musig module must take great care to make sure of the following: | ||
|
|
||
| 1. A unique nonce per signing session is generated in `secp256k1_musig_nonce_gen`. | ||
| See the corresponding comment in `include/secp256k1_musig.h` for how to ensure that. | ||
| 2. The `secp256k1_musig_secnonce` structure is never copied or serialized. | ||
| See also the comment on `secp256k1_musig_secnonce` in `include/secp256k1_musig.h`. | ||
| 3. Opaque data structures are never written to or read from directly. | ||
| Instead, only the provided accessor functions are used. | ||
|
|
||
| ## Key Aggregation and (Taproot) Tweaking | ||
|
|
||
| Given a set of public keys, the aggregate public key is computed with `secp256k1_musig_pubkey_agg`. | ||
| A plain tweak can be added to the resulting public key with `secp256k1_ec_pubkey_tweak_add` by setting the `tweak32` argument to the hash defined in BIP 32. Similarly, a Taproot tweak can be added with `secp256k1_xonly_pubkey_tweak_add` by setting the `tweak32` argument to the TapTweak hash defined in BIP 341. | ||
|
|
||
| ## Signing | ||
|
|
||
| This is covered by `examples/musig.c`. | ||
| Essentially, the protocol proceeds in the following steps: | ||
|
|
||
| 1. Generate a keypair with `secp256k1_keypair_create` and obtain the public key with `secp256k1_keypair_pub`. | ||
| 2. Call `secp256k1_musig_pubkey_agg` with the pubkeys of all participants. | ||
| 3. Optionally add a (Taproot) tweak with `secp256k1_musig_pubkey_xonly_tweak_add` and a plain tweak with `secp256k1_musig_pubkey_ec_tweak_add`. | ||
| 4. Generate a pair of secret and public nonce with `secp256k1_musig_nonce_gen` and send the public nonce to the other signers. | ||
| 5. Someone (not necessarily the signer) aggregates the public nonce with `secp256k1_musig_nonce_agg` and sends it to the signers. | ||
| 6. Process the aggregate nonce with `secp256k1_musig_nonce_process`. | ||
| 7. Create a partial signature with `secp256k1_musig_partial_sign`. | ||
| 8. Verify the partial signatures (optional in some scenarios) with `secp256k1_musig_partial_sig_verify`. | ||
| 9. Someone (not necessarily the signer) obtains all partial signatures and aggregates them into the final Schnorr signature using `secp256k1_musig_partial_sig_agg`. | ||
|
|
||
| The aggregate signature can be verified with `secp256k1_schnorrsig_verify`. | ||
|
|
||
| Note that steps 1 to 5 can happen before the message to be signed is known to the signers. | ||
| Therefore, the communication round to exchange nonces can be viewed as a pre-processing step that is run whenever convenient to the signers. | ||
| This disables some of the defense-in-depth measures that may protect against API misuse in some cases. | ||
| Similarly, the API supports an alternative protocol flow where generating the aggregate key (steps 1 to 3) is allowed to happen after exchanging nonces (steps 4 to 5). | ||
|
|
||
| ## Verification | ||
|
|
||
| A participant who wants to verify the partial signatures, but does not sign itself may do so using the above instructions except that the verifier skips steps 1, 4 and 7. |
Oops, something went wrong.