Procedure of Identification at gov.gr via winbank Credentials
The Greek State has created the website gov.gr which offers citizens an ever-expanding group of online services.
Login to the gov.gr can be done via winbank credentials for the Solemn Declaration and Authorization services. So you can, easily and quickly, issue electronically, a valid solemn declaration and an authorization letter, without visiting a Citizens' Service Centre (KEΠ) or a police station, to certify the authenticity of your signature.
If you do not have winbank credentials you can register online. The only condition is that you must have an active debit card in your possession and have declared your mobile phone to Piraeus Bank. So you can easily, in just a few minutes, register online for winbank credentials.
See the steps here and register online for winbank.