A public key is used in asymmetric cryptosystems and is needed to verify digital signatures or to encrypt data. There always exists a cryptographically linked private key to a public key.
A digital signature is a cryptographical scheme to verify the authenticity and integrity of digital data or documents and also to check the identity of the signer. In sproof the signer is represented by a profile. With a sproof profile you can register and digitally sign documents and data.