1 files changed, 51 insertions, 0 deletions
diff --git a/src/wallet/external_signer.cpp b/src/wallet/external_signer.cpp
index baf97700e7..3396111760 100644
--- a/src/wallet/external_signer.cpp
+++ b/src/wallet/external_signer.cpp
@@ -3,6 +3,10 @@
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 #include <chainparams.h>
+#include <core_io.h>
+#include <psbt.h>
+#include <util/strencodings.h>
+#include <util/system.h>
 #include <wallet/external_signer.h>
 
 ExternalSigner::ExternalSigner(const std::string& command, const std::string& fingerprint, std::string chain, std::string name): m_command(command), m_fingerprint(fingerprint), m_chain(chain), m_name(name) {}
@@ -65,4 +69,51 @@ UniValue ExternalSigner::GetDescriptors(int account)
     return RunCommandParseJSON(m_command + " --fingerprint \"" + m_fingerprint + "\"" + NetworkArg() + " getdescriptors --account " + strprintf("%d", account));
 }
 
+bool ExternalSigner::SignTransaction(PartiallySignedTransaction& psbtx, std::string& error)
+{
+    // Serialize the PSBT
+    CDataStream ssTx(SER_NETWORK, PROTOCOL_VERSION);
+    ssTx << psbtx;
+
+    // Check if signer fingerprint matches any input master key fingerprint
+    bool match = false;
+    for (unsigned int i = 0; i < psbtx.inputs.size(); ++i) {
+        const PSBTInput& input = psbtx.inputs[i];
+        for (auto entry : input.hd_keypaths) {
+            if (m_fingerprint == strprintf("%08x", ReadBE32(entry.second.fingerprint))) match = true;
+        }
+    }
+
+    if (!match) {
+        error = "Signer fingerprint " + m_fingerprint + " does not match any of the inputs:\n" + EncodeBase64(ssTx.str());
+        return false;
+    }
+
+    std::string command = m_command + " --stdin --fingerprint \"" + m_fingerprint + "\"" + NetworkArg();
+    std::string stdinStr = "signtx \"" + EncodeBase64(ssTx.str()) + "\"";
+
+    const UniValue signer_result = RunCommandParseJSON(command, stdinStr);
+
+    if (find_value(signer_result, "error").isStr()) {
+        error = find_value(signer_result, "error").get_str();
+        return false;
+    }
+
+    if (!find_value(signer_result, "psbt").isStr()) {
+        error = "Unexpected result from signer";
+        return false;
+    }
+
+    PartiallySignedTransaction signer_psbtx;
+    std::string signer_psbt_error;
+    if (!DecodeBase64PSBT(signer_psbtx, find_value(signer_result, "psbt").get_str(), signer_psbt_error)) {
+        error = strprintf("TX decode failed %s", signer_psbt_error);
+        return false;
+    }
+
+    psbtx = signer_psbtx;
+
+    return true;
+}
+
 #endif