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Mega has launched

mega.co.nz

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Re: Mega has launched

#91

Post by cryptox »

jiggy2011 wrote: post #62
gjulianm wrote: post #48

I just found a weird things on they ToS [1] ... 8. Our service may automatically delete a piece of data you upload or give someone else access to where it determines that that data is an exact duplicate of original data already on our service. In that case, you will access that original data. Duplicate check, I get that. But, how do they do it? They say the files are encrypted on the browser, so if I upload file X an…

Possibly convergent encryption, basically when you encrypt the file you use a hash of the file as the key. This key can then be encrypted with several different passwords meaning that several people can decrypt this file.

Wouldn't this allow MEGA to also get a copy of the key so they can decrypt your data?

Re: Mega has launched

#92

Post by icebraining »

zalew wrote: post #85
gee_totes wrote: post #70

Earlier quoted context omitted.

Really? I'm on FF3 and I didn't get a notice, which was quite surprising. File upload didn't work though....

wow, that's even weirder. btw thanks for the downvote, whoever that was.

Resist complaining about being downmodded. It never does any good, and it makes boring reading.

http://ycombinator.com/newsguidelines.html

Re: Mega has launched

#93

Post by pyre »

g_lined wrote: post #82
Alphasite_ wrote: post #37

How exactly does this work, if they don't have access to the original? > 8. Our service may automatically delete a piece of data you upload or give someone else access to where it determines that that data is an exact duplicate of original data already on our service. In that case, you will access that original data.

They take a hash of every X MB of your data before upload. If the hash already exists, then they don't upload it. You just get added to the access list for that particular chunk along with the others who have uploaded it.

Seems unlikely that there would be many collisions though...

Re: Mega has launched

#95

Post by cynicalkane »

cryptox wrote: post #91
jiggy2011 wrote: post #62

Earlier quoted context omitted.

Possibly convergent encryption, basically when you encrypt the file you use a hash of the file as the key. This key can then be encrypted with several different passwords meaning that several people can decrypt this file.

Wouldn't this allow MEGA to also get a copy of the key so they can decrypt your data?

Mega would be storing copies of the key that can only be decrypted with a password.

Re: Mega has launched

#96

Post by jiggy2011 »

cryptox wrote: post #91
jiggy2011 wrote: post #62

Earlier quoted context omitted.

Possibly convergent encryption, basically when you encrypt the file you use a hash of the file as the key. This key can then be encrypted with several different passwords meaning that several people can decrypt this file.

Wouldn't this allow MEGA to also get a copy of the key so they can decrypt your data?

Only if they had a copy of the original plaintext file.

Re: Mega has launched

#97

Post by zalew »

icebraining wrote: post #92
zalew wrote: post #85

Earlier quoted context omitted.

wow, that's even weirder. btw thanks for the downvote, whoever that was.

Resist complaining about being downmodded. It never does any good, and it makes boring reading. http://ycombinator.com/newsguidelines.html

I'm sorry, officer.

Re: Mega has launched

#98

Post by jiggy2011 »

politician wrote: post #83
gjulianm wrote: post #48

I just found a weird things on they ToS [1] ... 8. Our service may automatically delete a piece of data you upload or give someone else access to where it determines that that data is an exact duplicate of original data already on our service. In that case, you will access that original data. Duplicate check, I get that. But, how do they do it? They say the files are encrypted on the browser, so if I upload file X an…

"A node token ("magic cookie") grants access to a subtree of the issuing user's filesystem. An associated symmetric key is required to decrypt and/or store decryptable data." https://mega.co.nz/#developers Apparently, they use unsalted symmetric key encryption which allows them to discover [hash(file), password] duplicates. By comparison, the old Megaupload would apparently deduplicate based on [hash(file)] matches.…

I'm not entirely sure what they mean by a "magic cookie" here.

The document does say it uses public/private keys for data transfer. You would not usually use public/private for data storage because of the huge keysizes required.

Re: Mega has launched

#100

Post by beala »

jiggy2011 wrote: post #88
beala wrote: post #78

Earlier quoted context omitted.

Deriving the key from the plaintext + the ciphertext is called a known-plaintext attack [1]. AES isn't vulnerable to this. [1] http://en.wikipedia.org/wiki/Known-plaintext_attack#Present_...

It is if you know that the key is derived directly and deterministically from the plaintext itself. Of course this will only give you the key to that one particular file, not any other files that you do not have yourself.

Ah I see this was in reference to your convergent encryption post above. Point taken.

Assuming that it works this way, it would allow Mega to figure out if you own a known "bad" file. Just take something like "New_Jay-Z_Album.zip," hash it, and try the hash against your encrypted files. It seems like Kim is trying to avoid this problem.

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