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Re: Secret Sharing
From: Nir Izraeli <nirizr () gmail com>
Date: Sat, 03 Aug 2013 21:04:19 +0300

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On 8/1/13 7:01 PM, Jamie Riden wrote:
The answer is, I can't think of a better way of doing it. I
believe this is how EFS, etc. work - you have a single symmetric
encryption key and you encrypt this with the public key of anyone
who you want to be able to read the file.

+1.

One note though: you should get the PK{A,B} directly from the client
and not from the cloud service, if you want to avoid trusting the
cloud. the way you described it lets the cloud service hand out it's
own public key and then encrypt with B's PK afterwards.

But it's been a while since I read up on this, so I suggest you do
a sanity check.

cheers, Jamie

On 1 August 2013 15:48, saghar estehghari <s.estehghari () gmail com>
wrote:
Hi,

I'm working on a project which involves security of the cloud
data.

The scenario is as follows:

Users A and B have registered to a cloud service (cloud assumed
to be semi-trusted). A and B both have secret keys (KA and KB)
(for symmetric encryption) and public keys (PKA and PKB) on the
cloud server. KA and KB are each encrypted with the passwords of
A and B.

Now consider A wants to share a file F that is encrypted with key
K (K is generate randomly by A). Now K should be shared securely
with B over the cloud (we consider that B is not online at the
time of sharing). To do this one option would be encrypting K
with PKB which should be decrypted by B when he gets online.
However this option seems to be complicated for my client.

I was wondering whether you have better options in mind that
could help me. Please let me know if the explantation is not
clear.

Thanks



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