Identity Lock Key
The Identity Lock Key (ILK) is used to secure a user's identity association with each site where they use SQRL. The IUK and ILK together form a Curve25519 key pair. During identity association, it is combined with a Random Lock Key to create a Verify Unlock Key.
tmp = CurvePrivateKey( IUK ); ILK = CurvePublicKey( tmp );
The ILK is stored in the Type 1 block of the Secure Storage System.