Pip takes several steps to prevent people from finding out who Magwitch is. These steps are necessary, because under the conditions of Magwitch’s expulsion to Australia, he cannot return to London. So Magwitch wears a hat and an assumed name, Provis. He pretends to be Pip’s uncle. Pip only takes him out after dark, and only tells Herbert Pocket. Jaggers assists with some of the subterfuge.
Magwitch does not seem to be as nervous as Pip. He seems to think it will be easy to disguise himself, and trusts Pip to figure it out.
Dear boy,” he returned, “there's disguising wigs can be bought for money, and there's hair powder, and spectacles, and black clothes—shorts and what not. Others has done it safe afore, and what others has done afore, others can do agen. As to the where and how of living, dear boy, give me your own opinions on it.” (ch 40, enotes etext 224)
Pip decides that Magwitch will be no help, although he does make Herbert Pocket swear on a Bible, and plans to find him a quiet lodging nearby.