From 77daf867234c0a85dae328b62cb36984eca58667 Mon Sep 17 00:00:00 2001
From: Jonathan Naylor <naylorjs@yahoo.com>
Date: Mon, 14 Dec 2020 12:22:43 +0000
Subject: [PATCH] Decode encrypted POCSAG messages (thanks to JG1UAA for the
 code).

---
 POCSAGControl.cpp | 23 +++++++++++++++++++++--
 POCSAGControl.h   |  4 +++-
 2 files changed, 24 insertions(+), 3 deletions(-)

diff --git a/POCSAGControl.cpp b/POCSAGControl.cpp
index 703a7ad..afa9050 100644
--- a/POCSAGControl.cpp
+++ b/POCSAGControl.cpp
@@ -1,5 +1,5 @@
 /*
-*	Copyright (C) 2018,2019 Jonathan Naylor, G4KLX
+*	Copyright (C) 2018,2019,2020 Jonathan Naylor, G4KLX
 *
 *	This program is free software; you can redistribute it and/or modify
 *	it under the terms of the GNU General Public License as published by
@@ -147,10 +147,23 @@ bool CPOCSAGControl::readNetwork()
 
 	addAddress(functional, output->m_ric, output->m_buffer);
 
+	std::string out;
 	switch (functional) {
 		case FUNCTIONAL_ALPHANUMERIC:
 			output->m_text = std::string((char*)(data + 4U), length - 4U);
-			LogDebug("Message to %07u, func Alphanumeric: \"%s\"", output->m_ric, output->m_text.c_str());
+			switch (output->m_ric) {
+			case 4512U:
+				decodeROT1(output->m_text, 3U, out);
+				LogDebug("Message to %07u, func Alphanumeric: (%u) \"%s\"", output->m_ric, output->m_text.at(1U) - 0x1FU, out.c_str());
+				break;
+			case 4520U:
+				decodeROT1(output->m_text, 2U, out);
+				LogDebug("Message to %07u, func Alphanumeric: (%u-%u) \"%s\"", output->m_ric, output->m_text.at(0U) - 0x1FU, output->m_text.at(1U) - 0x20U, out.c_str());
+				break;
+			default:
+				LogDebug("Message to %07u, func Alphanumeric: \"%s\"", output->m_ric, output->m_text.c_str());
+				break;
+			}
 			packASCII(output->m_text, output->m_buffer);
 			break;
 		case FUNCTIONAL_NUMERIC:
@@ -483,3 +496,9 @@ void CPOCSAGControl::enable(bool enabled)
 
 	m_enabled = enabled;
 }
+
+void CPOCSAGControl::decodeROT1(const std::string& in, unsigned int start, std::string& out) const
+{
+	for (size_t i = start; i < in.length(); i++)
+		out += in.at(i) - 1U;
+}
diff --git a/POCSAGControl.h b/POCSAGControl.h
index f101ba5..7f585e8 100644
--- a/POCSAGControl.h
+++ b/POCSAGControl.h
@@ -1,5 +1,5 @@
 /*
-*   Copyright (C) 2018,2019 by Jonathan Naylor G4KLX
+*   Copyright (C) 2018,2019,2020 by Jonathan Naylor G4KLX
 *
 *   This program is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU General Public License as published by
@@ -81,6 +81,8 @@ private:
 	bool openFile();
 	bool writeFile(const unsigned char* data);
 	void closeFile();
+
+	void decodeROT1(const std::string& in, unsigned int start, std::string& out) const;
 };
 
 #endif