Unfortunately I'm not ...

One of my freelance proofreading clients (a small publisher) has asked me to sign a confidentiality agreement. Basically, if I ever leaked any information publicly in advance of a book's publication date, this agreement would give the publisher the right to recover unlimited damages from me.

Obviously I would never knowingly breach confidentiality but I'm uneasy about signing this document. It basically gives the client the right to sue me for as much as they like if anything goes wrong.

Has anyone else been asked to sign a document like this? Any thoughts about what I should do?

Thanks!