Lots of websites offer upload space for you to store files. A few even claim to store your files securely. Even fewer explain how exactly what secure means. A securely stored file must have at least three characteristics. It must be unreadable to unauthorized parties, it must be tamper resistant, and it must be available when needed.
Making a file unreadable to unauthorized parties requires encryption. The encryption algorithm used must be strong, such as 256-bit AES. The file must be encrypted while it is being moved (in-flight) between computers using SSL. More importantly, the file must remain encrypted while it is stored (at- rest).
Making a file tamper resistant requires taking a digital signature. This signature is created using a hash function, which is a mathematical procedure that converts a large amount of data (your file) into a small unique data value (your signature). This same procedure is used by criminal forensic specialists to ensure that digital evidence remains tamper free. A digital signature of your file should be taken immediately after it’s uploaded and again just before it’s downloaded. If the two signatures do not match, your file must not be downloaded.
Making sure your files are available when needed requires that a regular backup be taken. In most cases a periodic (i.e. weekly) backup may suffice. However, under high volume conditions this method may be inadequate. A more robust approach requires that data files be stored within an infrastructure that is both redundant and distributed. This means that multiple copies of data files (redundant) are stored in geographically separate locations (distributed). If a file is lost or destroyed in one location it is immediately available from another location.
Make sure that your service provider clearly states how your files are stored. If nothing is mentioned about these safety measures, it’s highly likely that no precautions are being taken. If your file is intercepted by a hacker, you may not get a second chance.
James Bell
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