Encrypting Cloud Files on Android, BlackBerry, Windows Phone and iPad / iPhone

One of the issues that becomes apparent with more users choosing to work from mobile phones and tablets is the issue of security. Sometimes these devices can end up in the wrong hands and when that happens it is reasonable to take precautions about how can open and gain access to files you have stored in the Cloud.

The secondary security concern can be with Cloud the Providers themselves. Users often want to protect certain  files on the actual Cloud where they reside, and to that end they can want to use encryption independent of the Cloud Provider.

This particular use case can be solved by using the Cloud encryption service that SMEStorage provides. This features is provided to free, personal, and Cloud File Server users.

Encryption works when users upload files from SMEStorage web or desktop access Client, to any of the 35 Cloud Storage and Saas Providers that SMEStorage supports. Users connect over SSL and assign files a key phrase to file that are uploaded. This key phrase is not stored anywhere on the SME service, and files are encrypted as they stream through the SME service to the remote Cloud Provider.

When web, windows / Mac / Linux, or iOS, Android, WP7 or BlackBerry mobile clients are used to try and access an encrypted file then a password prompt will be presented and the file will be unable to be accessed until this key phrase is entered. If the files is share using a file share link then anyone who then tries to open the file will also be required to enter the key phrase before accessing the file.


SMEStorage uses AES-256 encryption using the Rijndael cipher, with Cipher Block Chaining (CBC) where the block size is 16 bytes. The cipher Rijndael consists of:

– an initial Round Key addition
– Nr-1Rounds
– a final round.

The chaining variable goes into the “input” and the message block goes into the “Cipher Key. The likelihood of recovering a file that has been encrypted using our encryption is fairly remote. The most efficient key-recovery attack for Rijndael is exhaustive key search. The expected effort of exhaustive key search depends on the length of the Cipher Key and for a 16-byte key, 2 to the power of 127 applications of Rijndael.

Any AES-256 decryption tool that supports the Rijndael cipher with 16 byte blocksizes can be used to un-encrypt files. For example the popular freeware file manager Total Commander has a free plugin to handle such decryption.

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