1 files changed, 93 insertions, 0 deletions
diff --git a/src/common/signmessage.cpp b/src/common/signmessage.cpp
new file mode 100644
index 0000000000..1612751e44
--- /dev/null
+++ b/src/common/signmessage.cpp
@@ -0,0 +1,93 @@
+// Copyright (c) 2009-2010 Satoshi Nakamoto
+// Copyright (c) 2009-2022 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <common/signmessage.h>
+#include <hash.h>
+#include <key.h>
+#include <key_io.h>
+#include <pubkey.h>
+#include <uint256.h>
+#include <util/strencodings.h>
+
+#include <cassert>
+#include <optional>
+#include <string>
+#include <variant>
+#include <vector>
+
+/**
+ * Text used to signify that a signed message follows and to prevent
+ * inadvertently signing a transaction.
+ */
+const std::string MESSAGE_MAGIC = "Bitcoin Signed Message:\n";
+
+MessageVerificationResult MessageVerify(
+    const std::string& address,
+    const std::string& signature,
+    const std::string& message)
+{
+    CTxDestination destination = DecodeDestination(address);
+    if (!IsValidDestination(destination)) {
+        return MessageVerificationResult::ERR_INVALID_ADDRESS;
+    }
+
+    if (std::get_if<PKHash>(&destination) == nullptr) {
+        return MessageVerificationResult::ERR_ADDRESS_NO_KEY;
+    }
+
+    auto signature_bytes = DecodeBase64(signature);
+    if (!signature_bytes) {
+        return MessageVerificationResult::ERR_MALFORMED_SIGNATURE;
+    }
+
+    CPubKey pubkey;
+    if (!pubkey.RecoverCompact(MessageHash(message), *signature_bytes)) {
+        return MessageVerificationResult::ERR_PUBKEY_NOT_RECOVERED;
+    }
+
+    if (!(PKHash(pubkey) == *std::get_if<PKHash>(&destination))) {
+        return MessageVerificationResult::ERR_NOT_SIGNED;
+    }
+
+    return MessageVerificationResult::OK;
+}
+
+bool MessageSign(
+    const CKey& privkey,
+    const std::string& message,
+    std::string& signature)
+{
+    std::vector<unsigned char> signature_bytes;
+
+    if (!privkey.SignCompact(MessageHash(message), signature_bytes)) {
+        return false;
+    }
+
+    signature = EncodeBase64(signature_bytes);
+
+    return true;
+}
+
+uint256 MessageHash(const std::string& message)
+{
+    HashWriter hasher{};
+    hasher << MESSAGE_MAGIC << message;
+
+    return hasher.GetHash();
+}
+
+std::string SigningResultString(const SigningResult res)
+{
+    switch (res) {
+        case SigningResult::OK:
+            return "No error";
+        case SigningResult::PRIVATE_KEY_NOT_AVAILABLE:
+            return "Private key not available";
+        case SigningResult::SIGNING_FAILED:
+            return "Sign failed";
+        // no default case, so the compiler can warn about missing cases
+    }
+    assert(false);
+}