to another's data. Additionally, even Service Providers must not be able to access their customer's data without the customer's permission. Enterprise-class cloud backup An enterprise-class cloud backup solution must include an on-premises cache, to mitigate any issues due to inconsistent Internet connectivity. Hybrid cloud backup works by storing data to local disk so that the backup can be captured at high speed, and then either the backup software or a D2D2C (Disk to Disk to Cloud) appliance encrypts and transmits data to a service provider. This adds protection against local disasters. Recent backups are retained locally, to speed data recovery operations. There are a number of cloud storage appliances on the market that can be used as a backup target, including appliances from CTERA Networks, StorSimple and TwinStrata. Hybrid cloud backup is also beneficial for enterprise users who have security concerns. When storing data locally before sending it to the cloud, backup users can perform the necessary encryption operations, incl. technologies like: Data encryption cipher (AES 128, AES192, AES256 or blowfish) Windows Encrypting File System (EFS) Verification of files previously catalogued, permitting a Tripwire-like capability CRAM-MD5 password authentication between each component (storage, client and cloud) Configurable TLS (SSL) communications encryption between each component (storage, client and cloud) Computation of MD5 or SHA1 signatures of the file data, if configured Data encryption should additionally be applied when you choose a public cloud service provider. The same is important for the compression of backup data. The local backup cache is used to compress the data before sending it to the cloud in order to lower the network bandwidth load and improve backup speed. This becomes critical for enterprises which backup huge databases like Oracle or MS SQL or huge files like virtual machine images or mail server databases (EDB files of Exchange). Recent improvements in CPU availability allow increased use of software agents instead of hardware appliances for enterprise cloud backup. The software-only approach can offer advantages including decreased complexity, simple scalability, significant cost savings and improved data recovery times. Typical features Encryption Data should be encrypted before it is sent across the internet, and it should be stored in its encrypted state. Encryption should be at least 256 bits, and the user should have the option of using his own encryption key, which should never be sent to the server. Network backup A backup service supporting network backup can back up