From aab88fa8ebd9af971c1fc9e2f81b9cd9db538f90 Mon Sep 17 00:00:00 2001
From: Dirk Engling <erdgeist@erdgeist.org>
Date: Sun, 17 Jan 2021 01:12:38 +0100
Subject: Add v2 with GCM_IV_LENGTH of 96 bits == 12 bytes for performance and
 interop reasons

---
 receiver.cpp | 26 ++++++++++++++------------
 1 file changed, 14 insertions(+), 12 deletions(-)

diff --git a/receiver.cpp b/receiver.cpp
index 2fa2d8a..aaf9673 100644
--- a/receiver.cpp
+++ b/receiver.cpp
@@ -80,7 +80,7 @@ static time_t now() {
 }
 
 // Constants
-enum { SESSION_ID_LENGTH = 8, AES_KEY_LENGTH = 16, GCM_IV_LENGTH = 16, GCM_TAG_LENGTH = 16, MIN_PACKET_SIZE = 40 };
+enum { SESSION_ID_LENGTH = 8, AES_KEY_LENGTH = 16, GCM_IV_LENGTH_LEGACY = 16, GCM_IV_LENGTH = 12, GCM_TAG_LENGTH = 16, MIN_PACKET_SIZE = 40 };
 enum { DIRNAME_LENGTH = 10, FILENAME_LENGTH = 73, SIDOFFS = 20, KEYOFFS = 37 };
 
 class Session {
@@ -132,19 +132,21 @@ public:
         return open((_dirname + "/" + _filename).c_str(), O_WRONLY | O_APPEND | O_CREAT, 0755);
     }
 
-    void write_log(const uint8_t *packet, size_t len) {
+    void write_log(const uint8_t *packet, size_t len, int version = 2) {
+        const size_t iv_len = ( version == 1 ? GCM_IV_LENGTH_LEGACY : GCM_IV_LENGTH);
+
         // First check if the packet holds enough space for session id, iv and at least one gcm block
-        if (len < GCM_IV_LENGTH + GCM_TAG_LENGTH) {
+        if (len < iv_len + GCM_TAG_LENGTH) {
             std::cerr << "Error: Short packet, size " << len << std::endl;
             return;
         }
 
         const uint8_t *iv = packet;
-        const uint8_t *tag = packet + GCM_IV_LENGTH;
-        const uint8_t *payload = packet + GCM_IV_LENGTH + GCM_TAG_LENGTH;
-        len -= GCM_IV_LENGTH + GCM_TAG_LENGTH;
+        const uint8_t *tag = packet + iv_len;
+        const uint8_t *payload = packet + iv_len + GCM_TAG_LENGTH;
+        len -= iv_len + GCM_TAG_LENGTH;
 
-        std::string ivs(packet, packet +GCM_IV_LENGTH);
+        std::string ivs(packet, packet + iv_len);
         if (_used_ivs.find(ivs) != _used_ivs.end()) {
             std::cerr << "Error: Session " << std::hex << _session_id << " reused IV. Dropping packet" << std::endl;
             return;
@@ -163,7 +165,7 @@ public:
         uint8_t *output = static_cast<uint8_t*>(alloca(len));
 
         // This should fail on invalid input sizes
-        switch (mbedtls_gcm_auth_decrypt(&_ctx, len, iv, GCM_IV_LENGTH, (uint8_t*)&_session_id, SESSION_ID_LENGTH, tag, GCM_TAG_LENGTH, payload, output))
+        switch (mbedtls_gcm_auth_decrypt(&_ctx, len, iv, iv_len, (uint8_t*)&_session_id, SESSION_ID_LENGTH, tag, GCM_TAG_LENGTH, payload, output))
         {
             case 0:
                 write(_fd, output, len);
@@ -325,13 +327,13 @@ int main() {
             if (session == g_sessions.end())
                 g_sessions[session_id] = std::make_unique<Session>(session_id, rsa_plain_text);
             break;
-        case 1: {
+        case 1:
+        case 2:
             if (session != g_sessions.end())
-                session->second->write_log(packet + 1 + SESSION_ID_LENGTH, len - 1 - SESSION_ID_LENGTH);
+                session->second->write_log(packet + 1 + SESSION_ID_LENGTH, len - 1 - SESSION_ID_LENGTH, static_cast<int>(packet[0]));
             else
-                std::cerr << "Error: Can't log to unknown session " << std::hex << session_id << std::endl;
+                std::cerr << "Error: Can't log to unknown session " << std::hex << session_id << std::dec << std::endl;
             break;
-            }
         default:
             break;
         }
-- 
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