Detailed error message for passphrases with null chars

Since users may have thought the null characters in their
passphrases were actually evaluated prior to this change,
they may be surprised to learn that their passphrases no
longer work. Give them feedback to explain how to remedy
the issue.

Author: john-moffett

src/qt/askpassphrasedialog.cpp

@@ -153,8 +153,19 @@ void AskPassphraseDialog::accept()
     case Unlock:
         try {
             if (!model->setWalletLocked(false, oldpass)) {
-                QMessageBox::critical(this, tr("Wallet unlock failed"),
-                                      tr("The passphrase entered for the wallet decryption was incorrect."));
+                // Check if the passphrase has a null character (see #27067 for details)
+                if (oldpass.find('\0') == std::string::npos) {
+                    QMessageBox::critical(this, tr("Wallet unlock failed"),
+                                          tr("The passphrase entered for the wallet decryption was incorrect."));
+                } else {
+                    QMessageBox::critical(this, tr("Wallet unlock failed"),
+                                          tr("The passphrase entered for the wallet decryption is incorrect. "
+                                             "It contains a null character (ie - a zero byte). "
+                                             "If the passphrase was set with a version of this software prior to 25.0, "
+                                             "please try again with only the characters up to — but not including — "
+                                             "the first null character. If this is successful, please set a new "
+                                             "passphrase to avoid this issue in the future."));
+                }
             } else {
                 QDialog::accept(); // Success
             }
@@ -173,8 +184,18 @@ void AskPassphraseDialog::accept()
             }
             else
             {
-                QMessageBox::critical(this, tr("Wallet encryption failed"),
-                                     tr("The passphrase entered for the wallet decryption was incorrect."));
+                // Check if the old passphrase had a null character (see #27067 for details)
+                if (oldpass.find('\0') == std::string::npos) {
+                    QMessageBox::critical(this, tr("Passphrase change failed"),
+                                          tr("The passphrase entered for the wallet decryption was incorrect."));
+                } else {
+                    QMessageBox::critical(this, tr("Passphrase change failed"),
+                                          tr("The old passphrase entered for the wallet decryption is incorrect. "
+                                             "It contains a null character (ie - a zero byte). "
+                                             "If the passphrase was set with a version of this software prior to 25.0, "
+                                             "please try again with only the characters up to — but not including — "
+                                             "the first null character."));
+                }
             }
         }
         else

src/wallet/rpc/encrypt.cpp

@@ -68,7 +68,17 @@ RPCHelpMan walletpassphrase()
         }
 
         if (!pwallet->Unlock(strWalletPass)) {
-            throw JSONRPCError(RPC_WALLET_PASSPHRASE_INCORRECT, "Error: The wallet passphrase entered was incorrect.");
+            // Check if the passphrase has a null character (see #27067 for details)
+            if (strWalletPass.find('\0') == std::string::npos) {
+                throw JSONRPCError(RPC_WALLET_PASSPHRASE_INCORRECT, "Error: The wallet passphrase entered was incorrect.");
+            } else {
+                throw JSONRPCError(RPC_WALLET_PASSPHRASE_INCORRECT, "Error: The wallet passphrase entered is incorrect. "
+                                                                    "It contains a null character (ie - a zero byte). "
+                                                                    "If the passphrase was set with a version of this software prior to 25.0, "
+                                                                    "please try again with only the characters up to — but not including — "
+                                                                    "the first null character. If this is successful, please set a new "
+                                                                    "passphrase to avoid this issue in the future.");
+            }
         }
 
         pwallet->TopUpKeyPool();
@@ -143,7 +153,16 @@ RPCHelpMan walletpassphrasechange()
     }
 
     if (!pwallet->ChangeWalletPassphrase(strOldWalletPass, strNewWalletPass)) {
-        throw JSONRPCError(RPC_WALLET_PASSPHRASE_INCORRECT, "Error: The wallet passphrase entered was incorrect.");
+        // Check if the old passphrase had a null character (see #27067 for details)
+        if (strOldWalletPass.find('\0') == std::string::npos) {
+            throw JSONRPCError(RPC_WALLET_PASSPHRASE_INCORRECT, "Error: The wallet passphrase entered was incorrect.");
+        } else {
+            throw JSONRPCError(RPC_WALLET_PASSPHRASE_INCORRECT, "Error: The old wallet passphrase entered is incorrect. "
+                                                                "It contains a null character (ie - a zero byte). "
+                                                                "If the old passphrase was set with a version of this software prior to 25.0, "
+                                                                "please try again with only the characters up to — but not including — "
+                                                                "the first null character.");
+        }
     }
 
     return UniValue::VNULL;