Deduplicate the message verifying code

The logic of verifying a message was duplicated in 2 places:

src/qt/signverifymessagedialog.cpp
  SignVerifyMessageDialog::on_verifyMessageButton_VM_clicked()

src/rpc/misc.cpp
  verifymessage()

with the only difference being the result handling. Move the logic into
a dedicated

src/util/message.cpp
  MessageVerify()

which returns a set of result codes, call it from the 2 places and just
handle the results differently in the callers.

1 files changed, 49 insertions, 0 deletions

diff --git a/src/util/message.h b/src/util/message.h
new file mode 100644
index 0000000000..6adda5d3ff
--- /dev/null
+++ b/src/util/message.h
@@ -0,0 +1,49 @@
+// Copyright (c) 2009-2010 Satoshi Nakamoto
+// Copyright (c) 2009-2020 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_UTIL_MESSAGE_H
+#define BITCOIN_UTIL_MESSAGE_H
+
+#include <string>
+
+extern const std::string strMessageMagic;
+
+/** The result of a signed message verification.
+ * Message verification takes as an input:
+ * - address (with whose private key the message is supposed to have been signed)
+ * - signature
+ * - message
+ */
+enum class MessageVerificationResult {
+    //! The provided address is invalid.
+    ERR_INVALID_ADDRESS,
+
+    //! The provided address is valid but does not refer to a public key.
+    ERR_ADDRESS_NO_KEY,
+
+    //! The provided signature couldn't be parsed (maybe invalid base64).
+    ERR_MALFORMED_SIGNATURE,
+
+    //! A public key could not be recovered from the provided signature and message.
+    ERR_PUBKEY_NOT_RECOVERED,
+
+    //! The message was not signed with the private key of the provided address.
+    ERR_NOT_SIGNED,
+
+    //! The message verification was successful.
+    OK
+};
+
+/** Verify a signed message.
+ * @param[in] address Signer's bitcoin address, it must refer to a public key.
+ * @param[in] signature The signature in base64 format.
+ * @param[in] message The message that was signed.
+ * @return result code */
+MessageVerificationResult MessageVerify(
+    const std::string& address,
+    const std::string& signature,
+    const std::string& message);
+
+#endif // BITCOIN_UTIL_MESSAGE_H