[#MuSig2AggregatePubkeys-04]
= MuSig2AggregatePubkeys
:mrdocs:

Compute the full aggregate pubkey from the given participant pubkeys in their current order. Outputs the secp256k1_musig_keyagg_cache and validates that the computed aggregate pubkey matches an expected aggregate pubkey. This is necessary for most MuSig2 operations.

== Synopsis

Declared in `<musig.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
std::optional<CPubKey>
MuSig2AggregatePubkeys(
    std::vector<CPubKey> const& pubkeys,
    xref:secp256k1_musig_keyagg_cache.adoc[secp256k1_musig_keyagg_cache]& keyagg_cache,
    std::optional<CPubKey> const& expected_aggregate);
----

== Return Value

The aggregate public key, or std::nullopt if aggregation fails or does not match expected_aggregate.

== Parameters

[cols="1,4"]
|===
| Name| Description
| *pubkeys*
| The participant public keys, in the order they should be aggregated.
| *keyagg_cache*
| Output cache populated with the aggregation state for later MuSig2 operations.
| *expected_aggregate*
| Optional aggregate pubkey to validate the computed result against.
|===


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