signingprovider: Add musig2 secnonces

Adds GetMuSig2SecNonces which returns secp256k1_musig_secnonce*, and
DeleteMuSig2Session which removes the MuSig2 secnonce from wherever it
was retrieved. FlatSigningProvider stores it as a pointer to a map of
session id to secnonce so that deletion will actually delete from the
object that actually owns the secnonces.

The session id is just a unique identifier for the caller to determine
what secnonces have been created.

src/script/signingprovider.cpp

@@ -58,6 +58,21 @@ std::vector<CPubKey> HidingSigningProvider::GetMuSig2ParticipantPubkeys(const CP
     return m_provider->GetMuSig2ParticipantPubkeys(pubkey);
 }
 
+void HidingSigningProvider::SetMuSig2SecNonce(const uint256& id, MuSig2SecNonce&& nonce) const
+{
+    m_provider->SetMuSig2SecNonce(id, std::move(nonce));
+}
+
+std::optional<std::reference_wrapper<MuSig2SecNonce>> HidingSigningProvider::GetMuSig2SecNonce(const uint256& session_id) const
+{
+    return m_provider->GetMuSig2SecNonce(session_id);
+}
+
+void HidingSigningProvider::DeleteMuSig2Session(const uint256& session_id) const
+{
+    m_provider->DeleteMuSig2Session(session_id);
+}
+
 bool FlatSigningProvider::GetCScript(const CScriptID& scriptid, CScript& script) const { return LookupHelper(scripts, scriptid, script); }
 bool FlatSigningProvider::GetPubKey(const CKeyID& keyid, CPubKey& pubkey) const { return LookupHelper(pubkeys, keyid, pubkey); }
 bool FlatSigningProvider::GetKeyOrigin(const CKeyID& keyid, KeyOriginInfo& info) const
@@ -94,6 +109,26 @@ std::vector<CPubKey> FlatSigningProvider::GetMuSig2ParticipantPubkeys(const CPub
     return participant_pubkeys;
 }
 
+void FlatSigningProvider::SetMuSig2SecNonce(const uint256& session_id, MuSig2SecNonce&& nonce) const
+{
+    if (!Assume(musig2_secnonces)) return;
+    musig2_secnonces->emplace(session_id, std::move(nonce));
+}
+
+std::optional<std::reference_wrapper<MuSig2SecNonce>> FlatSigningProvider::GetMuSig2SecNonce(const uint256& session_id) const
+{
+    if (!Assume(musig2_secnonces)) return std::nullopt;
+    const auto& it = musig2_secnonces->find(session_id);
+    if (it == musig2_secnonces->end()) return std::nullopt;
+    return it->second;
+}
+
+void FlatSigningProvider::DeleteMuSig2Session(const uint256& session_id) const
+{
+    if (!Assume(musig2_secnonces)) return;
+    musig2_secnonces->erase(session_id);
+}
+
 FlatSigningProvider& FlatSigningProvider::Merge(FlatSigningProvider&& b)
 {
     scripts.merge(b.scripts);
@@ -102,6 +137,8 @@ FlatSigningProvider& FlatSigningProvider::Merge(FlatSigningProvider&& b)
     origins.merge(b.origins);
     tr_trees.merge(b.tr_trees);
     aggregate_pubkeys.merge(b.aggregate_pubkeys);
+    // We shouldn't be merging 2 different sessions, just overwrite with b's sessions.
+    if (!musig2_secnonces) musig2_secnonces = b.musig2_secnonces;
     return *this;
 }
 

src/script/signingprovider.h

@@ -9,11 +9,15 @@
 #include <addresstype.h>
 #include <attributes.h>
 #include <key.h>
+#include <musig.h>
 #include <pubkey.h>
 #include <script/keyorigin.h>
 #include <script/script.h>
 #include <sync.h>
 
+#include <functional>
+#include <optional>
+
 struct ShortestVectorFirstComparator
 {
     bool operator()(const std::vector<unsigned char>& a, const std::vector<unsigned char>& b) const
@@ -162,6 +166,9 @@ public:
     virtual bool GetTaprootSpendData(const XOnlyPubKey& output_key, TaprootSpendData& spenddata) const { return false; }
     virtual bool GetTaprootBuilder(const XOnlyPubKey& output_key, TaprootBuilder& builder) const { return false; }
     virtual std::vector<CPubKey> GetMuSig2ParticipantPubkeys(const CPubKey& pubkey) const { return {}; }
+    virtual void SetMuSig2SecNonce(const uint256& id, MuSig2SecNonce&& nonce) const {}
+    virtual std::optional<std::reference_wrapper<MuSig2SecNonce>> GetMuSig2SecNonce(const uint256& session_id) const { return std::nullopt; }
+    virtual void DeleteMuSig2Session(const uint256& session_id) const {}
 
     bool GetKeyByXOnly(const XOnlyPubKey& pubkey, CKey& key) const
     {
@@ -206,6 +213,9 @@ public:
     bool GetTaprootSpendData(const XOnlyPubKey& output_key, TaprootSpendData& spenddata) const override;
     bool GetTaprootBuilder(const XOnlyPubKey& output_key, TaprootBuilder& builder) const override;
     std::vector<CPubKey> GetMuSig2ParticipantPubkeys(const CPubKey& pubkey) const override;
+    void SetMuSig2SecNonce(const uint256& id, MuSig2SecNonce&& nonce) const override;
+    std::optional<std::reference_wrapper<MuSig2SecNonce>> GetMuSig2SecNonce(const uint256& session_id) const override;
+    void DeleteMuSig2Session(const uint256& session_id) const override;
 };
 
 struct FlatSigningProvider final : public SigningProvider
@@ -216,6 +226,7 @@ struct FlatSigningProvider final : public SigningProvider
     std::map<CKeyID, CKey> keys;
     std::map<XOnlyPubKey, TaprootBuilder> tr_trees; /** Map from output key to Taproot tree (which can then make the TaprootSpendData */
     std::map<CPubKey, std::vector<CPubKey>> aggregate_pubkeys; /** MuSig2 aggregate pubkeys */
+    std::map<uint256, MuSig2SecNonce>* musig2_secnonces{nullptr};
 
     bool GetCScript(const CScriptID& scriptid, CScript& script) const override;
     bool GetPubKey(const CKeyID& keyid, CPubKey& pubkey) const override;
@@ -225,6 +236,9 @@ struct FlatSigningProvider final : public SigningProvider
     bool GetTaprootSpendData(const XOnlyPubKey& output_key, TaprootSpendData& spenddata) const override;
     bool GetTaprootBuilder(const XOnlyPubKey& output_key, TaprootBuilder& builder) const override;
     std::vector<CPubKey> GetMuSig2ParticipantPubkeys(const CPubKey& pubkey) const override;
+    void SetMuSig2SecNonce(const uint256& id, MuSig2SecNonce&& nonce) const override;
+    std::optional<std::reference_wrapper<MuSig2SecNonce>> GetMuSig2SecNonce(const uint256& session_id) const override;
+    void DeleteMuSig2Session(const uint256& session_id) const override;
 
     FlatSigningProvider& Merge(FlatSigningProvider&& b) LIFETIMEBOUND;
 };