When itвЂ™s BobвЂ™s turn, his computer goes through the same process and creates an encrypted file identical to AliceвЂ™s. Alice backs up first, so the song is reduced to a hash and then encrypted on her computer using that hash.

Say Alice and Bob each have the same song on their hard drives and both use Bitcasa. The hash is then used to encrypt the file using the Advanced Encryption Standard. ItвЂ™s called one-way because while each file generates a unique hash (there is a vanishingly small possibility that two different files could generate the same hash), there is no way to reconstruct the original from the hash. A mathematical function called a one-way hash reduces the file to a relatively short string of digits, typically 256 or 512 bits. The trick is to use the file to create its own encryption key. If you want to get deep into the weeds of the technology, it is explained in detail in this paper, but here is how it works. And if you donвЂ™t know what is in files, the sort of de-duping Bitcasa promises seems impossible.Д«ut, as Bitcasa CEO Tony Gauda explains in this TechCrunch interview, the company is taking advantage of a new and very clever trick called convergent encryption. If files are encrypted, no one but the owner, or someone else given the key, has any idea of what the contents are. The savings from de-duplication could be considerable because with entertainment content, large numbers of people tend to have copies of a small number of movies or songs.Д«ut at first glance, these claims seemed to be contradictory. Bitcasa said it provided privacy and security by encrypting all files, but was able to offer a very inexpensive service because it avoided the storage of duplicate files, especially music and movies. A startup named Bitcasa made a splash at the TechCrunch Disrupt conference last week by promising unlimited backups to the cloud for just $10 a month.

Bitcasa works