When user A wants to share the file with user B, user A "right clicks to get the sharing URL" and sends it to B. Then a user would have a local store (on his computer) of all the K f for all his files, along with a file ID. With this trick, the same file will always end up into the same encrypted format, which can then be uploaded and de-duplicated at will. There is a nifty trick which consists in using the hash of the file itself, with a proper hash function (say, SHA-256), as K f. To implement de-duplication and caching and, more importantly, sharing, it is necessary that every user encrypting a given file f will end up using the same K f.
The point of the thing is that Bitcasa does not know K f. If data is encrypted client-side, then there must be a secret key K f for that file. Let's see if there is a way to make these promises come true. The commercial ad you link to, and the company web site, are really short on information and waving "20 patents" as a proof of competence is weird: patents do not prove that the technology is good, only that there are some people who staked a few thousand dollars on the idea that the technology will sell well. However, I suspect they could be required to remove the file (under DMCA safe harbour rules) or possibly to retain the content but then log any accounts which upload/download it in the future. They wouldn't be able to decrypt it (without RIAA/MPAA giving them the hash/key), and (particularly if they aren't enforcing per-user quotas becausrer they offer "infinite storage") they might not have retained logs of which users uploaded/downloaded it. Bitcasa would then be able to confirm whether or not that file had been stored or not. the RIAA/MPAA would be able to come with a subpoena and an encrypted-with-its-own-hash copy of whatever song/movie they suspect people have copies of."patented de-duplication algorithms" - there must be more going on than the above to justify a patent - possibly de-duplication at a block, rather than file level?.also storing the collection of objid-to-filename-and-hash/key tuples, client-side encrypted with a passphrase. "accessible anywhere" - if the objid-to-filename-and-hash/key mapping is only on the client then the files are useless from other devices, which limits the usefulness of cloud storage."compression" - wouldn't work server-side (the encrypted content will not compress well) but could be applied client-side before encryption.Regarding some of the other features claimed in the article: specific song MP3s) they'd be able to decrypt and prove you had a copy, but first they'd need to know which cloud-storage object/file held which song.Ĭlients would need to keep the hash for each cloud-stored object, and their local name for it, of course, to be able to access and unencrypt it.
If the RIAA/MPAA knew the hashes of the files in question (well known for e.g. I haven't thought through the details, but if a secure hash of the file content were used as the key then any (and only) clients who "knew the hash" would be able to access the content.Įssentially the cloud storage would act as a collective partial (very sparse, in fact) rainbow table for the hashing function, allowing it to be "reversed".įrom the article: "Even if the RIAA and MPAA came knocking on Bitcasa’s doors, subpoenas in hand, all Bitcasa would have is a collection of encrypted bits with no means to decrypt them." - true because bitcasa don't hold the objectid/filename-to-hash/key mapping only their clients do (client-side).
Įdit3: have a the same question and different answers This makes Bitcasa a very bad choice when the files you want to be confidential are not original. I find the claim pretty dubious with the level of information I have now, anyone knows more about how they claim to achieve that? Had the founders of the company not had a serious business background (Verisign, Mastercard.) I would have classified the product as snake oil right away but maybe there is more to it.Įdit: found a worrying tweet : !/csoghoian/status/113753932400041984, encryption key per file would be derived from its hash, so definitely looking like not the place to store your torrented film collection, not that I would ever do that.Įdit2: We actually guessed it right, they used so called convergent encryption and thus someone owning the same file as you do can know wether yours is the same, since they have the key. A "soon to enter beta" online backup service, Bitcasa, claims to have both de-duplication (you don't backup something already in the cloud) and client side encryption.Ī patent search yields nothing with their company name but the patents may well be in the pipeline and not granted yet.
0 kommentar(er)
