ideas on cryptographyare interesting but not easy to grasp, i've got the question below.

digital singnature (e.g. implementation in .NET) applies to keyed hash algorthim underlying. since the represented content can't be revealed by its hash value at all, whyneed the hash value be extra encrypted?

the purpose of hashalgorthim is to establish the identity to itsrepresented content. even if the non-encrypted hash value is interrupted even altered by 3rd party, how could the harm really be done?

thx!

another thought. to make substantial difference between hash and keyed hash, it could be that while the key keeps change, the keyed hash changes as well even if the represented content is the same.

keyed hash makes better sense when the mechanism of easily updatable keys exists in the application and the represented content is relatively static. is that the main reason ?