One more tweak after thinking about related keys and key stream reuse. Just a precaution.

node/Packet.cpp

@@ -2028,7 +2028,9 @@ void Packet::cryptField(const void *key,unsigned int start,unsigned int len)
 	unsigned char mangledKey[32];
 	unsigned char macKey[32];
 	_salsa20MangleKey((const unsigned char *)key,mangledKey);
-    mangledKey[0] ^= 1; // slightly alter key for this use case as an added guard against key stream reuse
+    mangledKey[0] ^= 0x7f;
+    mangledKey[1] ^= ((start >> 8) & 0xff);
+    mangledKey[2] ^= (start & 0xff); // slightly alter key for this use case as an added guard against key stream reuse
 	Salsa20 s20(mangledKey,256,field(ZT_PACKET_IDX_IV,8));
 	s20.crypt12(ZERO_KEY,macKey,sizeof(macKey)); // discard the first 32 bytes of key stream (the ones use for MAC in armor()) as a precaution
     unsigned char *const ptr = field(start,len);