> What are all benefits this cryptography?

The core idea of public key crypto is that you have one operation
everybody can perform and one operation (usually the inverse or
something related) that only a selected group can perform. This may
include "everybody can encrypt, only I can decrypt" or "everybody can
verify but only my company can sign".

> Is possible to sign data by more than one user?
Absolutely. Just encode multiple signatures of the data. Or if you want
a signature to be identified with a group of persons, you can just share
the private signing key among them.

> Is possible encrypt data and decrypt it only if more than one user
> agree to decrypt?
In the secret-key setting this is no problem, if secret sharing is used.
In the public key setting, you'd need to encrypt a shared symmetric key,
e.g. encrypt the shares with different public keys and then a (nontrue)
subset of these private key holders would be required for message recovery.

BR

JPM


Am 26.05.2016 um 09:18 schrieb Andy:
> What are all benefits this cryptography? Is possible to sign data by
> more than one user? Is possible encrypt data and decrypt it only if
> more than one user agree to decrypt?
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