Secret key encryption is sometimes referred to as zero knowledge, meaning that only the user has the encryption key needed to decrypt the data. Since data is encrypted using the secret key, identical files encrypted with different keys will be different.
To be truly zero knowledge, the file hosting service must not be able to store the user's passwords or see their data even with physical access to the servers. For this reason, secret key encryption is considered the highest level of access security in cloud storage.
This form of encryption is rapidly gaining popularity, with companies such as SpiderOak being entirely zero knowledge file storage and sharing.
Since secret key encryption results in unique files, it makes data deduplication impossible and therefore may use more storage space.