3GPP 24.501 v20.0.0 — the document's own text
8.2.7.35 Ciphering key data
Taught in 4. Inside TS 24.501, the document at the centre (CT1 — the group that writes what your phone says, overview).
This IE is included if the network needs to send ciphering key data to the UE for ciphered broadcast assistance data.