(cryptography) An intermediate value used in forming a signature, unrelated to the contents of the message being signed.

Is there a word signed?

signed used as an adjective:

Having a signature, endorsed.

Is pre a real word?

a prefix occurring originally in loanwords from Latin, where it meant “before” (preclude; prevent); applied freely as a prefix, with the meanings “prior to,” “in advance of,” “early,” “beforehand,” “before,” “in front of,” and with other figurative meanings (preschool; prewar; prepay; preoral; prefrontal).