crypto-slides-07-pk0.1x1

crypto-slides-07-pk0.1x1 - Public Key Cryptography c...

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Unformatted text preview: Public Key Cryptography c circlecopyrt Eli Biham - August 18, 2010 199 Public Key Cryptography (7) Key Exchange All the ciphers mentioned previously require keys known a-priori to all the users, before they can encrypt and decrypt. To communicate securely, they need to have a common key, known only to them . Possible key exchanges : 1. An a-priori meeting to exchange keys. 2. Sending the keys by a special courier. 3. Using an already existing common key, to encrypt additional keys. c circlecopyrt Eli Biham - August 18, 2010 200 Public Key Cryptography (7) Key Exchange (cont.) The problem : A meeting is required between the users (or their couriers), in order to be able to communicate securely. Conclusion : Two users who have never met cannot communicate securely! c circlecopyrt Eli Biham - August 18, 2010 201 Public Key Cryptography (7) Example Two armies during a war. Unit 1 Unit 2 Enemy The enemy wins, since it found all the keys that our army use for communica- tion....
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crypto-slides-07-pk0.1x1 - Public Key Cryptography c...

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