bitcoin: support sending to silent payment addresses

messages/btc.proto

@@ -112,6 +112,7 @@ message BTCSignInitRequest {
     SAT = 1;
   }
   FormatUnit format_unit = 8;
+  bool contains_silent_payment_outputs = 9;
 }
 
 message BTCSignNextResponse {
@@ -135,6 +136,7 @@ message BTCSignNextResponse {
   // Previous tx's input/output index in case of PREV_INPUT or PREV_OUTPUT, for the input at `index`.
   uint32 prev_index = 5;
   AntiKleptoSignerCommitment anti_klepto_signer_commitment = 6;
+  bytes generated_output_pkscript = 7;
 }
 
 message BTCSignInputRequest {
@@ -158,6 +160,10 @@ enum BTCOutputType {
 }
 
 message BTCSignOutputRequest {
+  // https://github.com/bitcoin/bips/blob/master/bip-0352.mediawiki
+  message SilentPayment {
+    string address = 1;
+  }
   bool ours = 1;
   BTCOutputType type = 2; // if ours is false
   // 20 bytes for p2pkh, p2sh, pw2wpkh. 32 bytes for p2wsh.
@@ -167,6 +173,9 @@ message BTCSignOutputRequest {
   // If ours is true. References a script config from BTCSignInitRequest
   uint32 script_config_index = 6;
   optional uint32 payment_request_index = 7;
+    // If provided, `type` must be `P2TR` and the payload must be empty. The output's pkScript is
+  // returned BTCSignNextResponse.
+  SilentPayment silent_payment = 8;
 }
 
 message BTCScriptConfigRegistration {

src/CMakeLists.txt

@@ -334,6 +334,7 @@ add_custom_target(rust-bindgen
     --allowlist-function keystore_lock
     --allowlist-function keystore_create_and_store_seed
     --allowlist-function keystore_copy_seed
+    --allowlist-function keystore_secp256k1_get_private_key
     --allowlist-function keystore_get_bip39_mnemonic
     --allowlist-function keystore_get_bip39_word
     --allowlist-function keystore_get_ed25519_seed

src/keystore.c

@@ -1000,6 +1000,29 @@ bool keystore_secp256k1_schnorr_bip86_sign(
     return secp256k1_schnorrsig_verify(ctx, sig64_out, msg32, 32, &pubkey) == 1;
 }
 
+bool keystore_secp256k1_get_private_key(
+    const uint32_t* keypath,
+    const size_t keypath_len,
+    bool tweak_bip86,
+    uint8_t* key_out)
+{
+    if (tweak_bip86) {
+        secp256k1_keypair __attribute__((__cleanup__(_cleanup_keypair))) keypair = {0};
+        secp256k1_xonly_pubkey pubkey = {0};
+        if (!_schnorr_bip86_keypair(keypath, keypath_len, &keypair, &pubkey)) {
+            return false;
+        }
+        const secp256k1_context* ctx = wally_get_secp_context();
+        return secp256k1_keypair_sec(ctx, key_out, &keypair) == 1;
+    }
+    struct ext_key xprv __attribute__((__cleanup__(keystore_zero_xkey))) = {0};
+    if (!_get_xprv_twice(keypath, keypath_len, &xprv)) {
+        return false;
+    }
+    memcpy(key_out, xprv.priv_key + 1, 32);
+    return true;
+}
+
 #ifdef TESTING
 void keystore_mock_unlocked(const uint8_t* seed, size_t seed_len, const uint8_t* bip39_seed)
 {

src/keystore.h

@@ -303,6 +303,12 @@ USE_RESULT bool keystore_secp256k1_schnorr_bip86_sign(
     const uint8_t* msg32,
     uint8_t* sig64_out);
 
+USE_RESULT bool keystore_secp256k1_get_private_key(
+    const uint32_t* keypath,
+    size_t keypath_len,
+    bool tweak_bip86,
+    uint8_t* key_out);
+
 #ifdef TESTING
 /**
  * convenience to mock the keystore state (locked, seed) in tests.

src/rust/bitbox02-rust/Cargo.toml

@@ -32,6 +32,7 @@ util = { path = "../util" }
 erc20_params = { path = "../erc20_params", optional = true }
 binascii = { version = "0.1.4", default-features = false, features = ["encode"] }
 bitbox02-noise = {path = "../bitbox02-noise"}
+streaming-silent-payments = {path = "../streaming-silent-payments"}
 hex = { workspace = true }
 sha2 = { workspace = true }
 sha3 = { workspace = true, optional = true }