Following to their architectural design, they do not get access to any encryption key and no key leaves user device in unprotected form. Is not this enough to be advertised as "zero-knowledge" service provider?
Skycryptor provides zero-knowledge solution. It never can get access to user encryption keys or even search queries. Innovative key management solution allows to share encrypted files with contacts just via native cloud sharing experience and our proprietary searchable encryption algorithm keeps all your files just a few keyword away..