Add 'spec.md'

spec.md

@@ -0,0 +1,21 @@
+## Unencrypted
+The packet contains 6-byte set instructions. There may be multiple instructions, concatenated together.
+An instruction is:
+```
+12 bits - x
+12 bits - y
+24 bits - rgb
+```
+
+## Encrypted
+The encrypted protocol works by encapsulating an unencrypted packet.
+The format is as follows:
+```
+32 bytes - An X25519 public key.
+24 bytes - Cipher nonce.
+16 bytes - MAC
+rest     - Ciphertext
+```
+
+Please note that all operations are being done with the [Monocypher](https://monocypher.org) library.  
+Implementations using other libraries may be incompatible.