Header Protection (short header)
01smmmmm
1 byte
Dest CID
e.g. 8 bytes
PN
1-4 b
masked
Encrypted Payload + AEAD Tag
sample (16 bytes)
pn_offset
pn_offset + 4
AES-ECB(hp_key, sample)
mask
mask[0] ⊕ header → unmask mmmmm
mask[1..1+len] ⊕ PN bytes → packet number