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Add MuSig2 adaptor sig exercise in example code #188

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Add MuSig2 adaptor sig exercise in example code #188

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34 changes: 32 additions & 2 deletions examples/musig.c
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Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,7 @@
#include <secp256k1_musig.h>

#include "examples_util.h"
#include <string.h>

struct signer_secrets {
secp256k1_keypair keypair;
Expand Down Expand Up @@ -100,6 +101,19 @@ static int sign(const secp256k1_context* ctx, struct signer_secrets *signer_secr
/* The same for all signers */
secp256k1_musig_session session;

/* For adapter signature, committing to random scalar */
unsigned char presig[64];
int nonce_parity;
unsigned char adaptor_key[32];
unsigned char extracted_adaptor[32];
secp256k1_pubkey adaptor;
if (!fill_random(adaptor_key, sizeof(adaptor_key))) {
return 0;
}
if (!secp256k1_ec_pubkey_create(ctx, &adaptor, adaptor_key)) {
return 0;
}

for (i = 0; i < N_SIGNERS; i++) {
unsigned char seckey[32];
unsigned char session_id[32];
Expand Down Expand Up @@ -128,7 +142,7 @@ static int sign(const secp256k1_context* ctx, struct signer_secrets *signer_secr
if (!secp256k1_musig_nonce_agg(ctx, &agg_pubnonce, pubnonces, N_SIGNERS)) {
return 0;
}
if (!secp256k1_musig_nonce_process(ctx, &session, &agg_pubnonce, msg32, cache, NULL)) {
if (!secp256k1_musig_nonce_process(ctx, &session, &agg_pubnonce, msg32, cache, &adaptor)) {
return 0;
}
/* partial_sign will clear the secnonce by setting it to 0. That's because
Expand Down Expand Up @@ -158,7 +172,23 @@ static int sign(const secp256k1_context* ctx, struct signer_secrets *signer_secr
return 0;
}
}
return secp256k1_musig_partial_sig_agg(ctx, sig64, &session, partial_sigs, N_SIGNERS);

/* Since we are doing adaptor sig, complete pre-signature */
if (!secp256k1_musig_nonce_parity(ctx, &nonce_parity, &session)) {
return 0;
}
if (!secp256k1_musig_partial_sig_agg(ctx, presig, &session, partial_sigs, N_SIGNERS)) {
return 0;
}
if (!secp256k1_musig_adapt(ctx, sig64, presig, adaptor_key, nonce_parity)) {
return 0;
}
/* With sig64 "on-chain" now, other party can grab the revealed adaptor secret */
if (!secp256k1_musig_extract_adaptor(ctx, extracted_adaptor, sig64, presig, nonce_parity)) {
return 0;
}
assert(memcmp(extracted_adaptor, adaptor_key, sizeof(adaptor_key)) == 0);
return 1;
}

int main(void) {
Expand Down