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Edward avatar Crypto

Key distribution protocol involves only 2 parties, given E[k1,E(k2,m)]=E[k2, E(k1, m)]

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Edward

Given an one-key cipher such that: E[k1,E(k2,m)]=E[k2, E(k1, m)] Is there any key distribution protocol that involves only two parties (Alice and Bob) without the key distribution center? The protocol should allow Alice to send a session key to Bob with confidentiality using the one-key cipher.

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poncho avatar Crypto
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poncho

Is there any key distribution protocol that involves only two parties (Alice and Bob) without the key distribution center?

Yes, it's Shamir's Three Pass Protocol; it works exactly how you describe. It indeed provides confidentiality, assuming that the attacker cannot modify the messages, and assuming that the cipher it is based on is secure.

Now, it's not used in practice (at least, I've never seen it used); we generally use either a Diffie-Hellman exchange or public key encryption instead.

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