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Consider a scenario with two security levels, Alice and Bob. Bob is Alice's boss. Bob must be able to read Alice's documents but not write anything to her documents.

I am using encryption keys to encrypt all of Alice's data, and then giving Bob the private key/ However I have realised this will not stop him editing it, just giving him the public key would allow him to edit it but not see it.

Basically how would Bob be able to see and not edit Alice's files?

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@Rook No, we don't use a homework tag here, for good reason. –  Gilles Dec 8 '12 at 23:20
    
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Why weren't your two questions (how to stop write downs & how to stop read ups) combined into "How to enforce the Bell-LaPadula model?" –  Henning Klevjer Dec 9 '12 at 13:32

1 Answer 1

Alice has the private key and the boss the public. The boss can use the public key to read things Alice makes, but Alice is the only one that can encrypt her stuff with the private key. Even if the boss edits a file he will not be able to save it (re-encrypt it) because he does not hold the private key. Alice can read and write because she holds both the encryption and decryption key.

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thank you so much, how would i go about allowing alice to edit something the boss has done but not read it ? –  test1245 Dec 8 '12 at 21:47
    
You can't. You can't have write without read permissions. –  Lucas Kauffman Dec 8 '12 at 22:04
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not even using any encryption keys to achieve this ? and create a blind - write ? –  test1245 Dec 8 '12 at 22:13
    
Do you have any practical use for this? I mean a "blind write" is kind of silly if you don't know where you are writing to. –  Lucas Kauffman Dec 8 '12 at 22:38
    
@LucasKauffman there are a few valid scenarios where "blind write" does make very good sense. E.g. messaging, logging, ... –  AviD Dec 9 '12 at 11:55

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