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Overview of Key Establishment Techniques:Key Distribution, Key Agreement and PKI

We now begin our look at building protocols using the basic tools that we have discussed. The discussion in this lecture will focus on issues of key establishment and the associated notion of authentication These protocols are not real, but instead are meant to serve just as a high-level survey Later lectures will go into specific protocols and will uncover practical challenges faced when implementing these protocols | Overview of Key Establishment Techniques: Key Distribution, Key Agreement and PKI Wade Trappe Lecture Overview We now begin our look at building protocols using the basic tools that we have discussed. The discussion in this lecture will focus on issues of key establishment and the associated notion of authentication These protocols are not real, but instead are meant to serve just as a high-level survey Later lectures will go into specific protocols and will uncover practical challenges faced when implementing these protocols Key Establishment: The problem Securing communication requires that the data is encrypted before being transmitted. Associated with encryption and decryption are keys that must be shared by the participants. The problem of securing the data then becomes the problem of securing the establishment of keys. Task: If the participants do not physically meet, then how do the participants establish a shared key? Two types of key establishment: Key Agreement Key . | Overview of Key Establishment Techniques: Key Distribution, Key Agreement and PKI Wade Trappe Lecture Overview We now begin our look at building protocols using the basic tools that we have discussed. The discussion in this lecture will focus on issues of key establishment and the associated notion of authentication These protocols are not real, but instead are meant to serve just as a high-level survey Later lectures will go into specific protocols and will uncover practical challenges faced when implementing these protocols Key Establishment: The problem Securing communication requires that the data is encrypted before being transmitted. Associated with encryption and decryption are keys that must be shared by the participants. The problem of securing the data then becomes the problem of securing the establishment of keys. Task: If the participants do not physically meet, then how do the participants establish a shared key? Two types of key establishment: Key Agreement Key Distribution Key Distribution Key Agreement protocols: the key isn’t determined until after the protocol is performed. Key Distribution protocols: one party generates the key and distributes it to Bob and/or Alice (Shamir’s 3pass, Kerberos). Shamir’s Three-Pass Protocol: Alice generates and Bob generates . A key K is distributed by: Alice Bob Bob Calculates: Basic TTP Key Distribution KDC Ka Kb Step 1 Step 2 1. A Sends: {Request || IDA || IDB || N1} 2. KDC Sends: EKa[ KAB|| {Request || IDA || IDB || N1}||EKb(KAB, IDA)] Step 3 Step 4 3. A Sends: EKb(KAB, IDA) Step 5 4. B Sends: EKAB(N2) 5. A Sends: EKAB(f(N2)) Key Agreement In many scenarios, it is desirable for two parties to exchange messages in order to establish a shared secret that may be used to generate a key. The Diffie-Hellman (DH) protocol is a basic tool used to establish shared keys in two-party communication. Two parties, A and B, establish a shared secret by: The security of the DH scheme is based upon the intractibility of the .