ProtonMail has added a new contacts manager that they say is the first that includes zero access encryption and digital signature verification. This complements their email and VPN services.
ProtonMail Contacts, which has been in development foe a year or so is part of the recent Version 3.12 release of ProtonMail. As well as adding improved contacts functionality to ProtonMail there's a big push of bolstering security.
The new contact manager uses zero-access encryption. The protected contact fields are encrypted so you are able to decrypt and read them - not even ProtonMail can read them. Protected contact details are shown within an area with a lock icon.
While information such as a phone number can be protected other fields can;t. For example, it's not possible to encrypt email addresses as ProtonMail needs access to those in order to address a message.
ProtonMail Contact also uses digital signatures to verify the integrity of contacts data so that any tampering is detected. Digital signatures are used for all contact fields, including the email address.
There's more information on ProtonMail's blog.