20. When any portion of an electronic record is signed with a digital signature, the digital signature shall be treated as a secure electronic signature with respect to such portion of the record, if —
the digital signature was created during the operational period of a valid certificate and is verified by reference to the public key listed in such certificate; and
the certificate is considered trustworthy, in that it is an accurate binding of a public key to a person’s identity because —
the certificate was issued by a licensed certification authority operating in compliance with the regulations made under section 42 ;
the certificate was issued by a certification authority outside Singapore recognised for this purpose by the Controller pursuant to regulations made under section 43;
the certificate was issued by a department or ministry of the Government, an organ of State or a statutory corporation approved by the Minister to act as a certification authority on such conditions as he may by regulations impose or specify; or
the parties have expressly agreed between themselves (sender and recipient) to use digital signatures as a security procedure, and the digital signature was properly verified by reference to the sender’s public key.