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+File Format
+===========
+
+Header
+
+	 2 bytes header version (big endian uint16, currently 2)
+	16 bytes file id
+
+Data block
+
+	16 bytes GCM IV (nonce)
+	1-4096 bytes encrypted data
+	16 bytes GHASH
+
+
+Example: 1-byte file
+--------------------
+
+	Header     18 bytes
+	Data block 33 bytes
+
+Total: 51 bytes
+
+
+Example: 5000-byte file
+-----------------------
+
+	Header       18 bytes
+	Data block 4128 bytes
+	Data block  936 bytes
+
+Total: 5082 bytes