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Information and Network Security. Ch4: Confidentiality Using Conventional Encryption. Conventional encryption to provide confidentiality. Historically, the focus of cryptology has been on the use of conventional encryption to provide confidentiality.
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Information and Network Security Ch4: Confidentiality Using Conventional Encryption
Conventional encryption toprovide confidentiality. • Historically, the focus of cryptology has been on the use of conventional encryption to provide confidentiality. • Authorization, Integrity, Digital signatures, and the use of public-key encryption, have been included in the theory only in the last several decades.
Placement of EncryptionFunction • The location of encryption function is needed to be decided if the encryption is to be used to counter attacks on Confidentiality. • First, we have to find out the potential locations of security attacks. • Second, decide where to place the encryption function.
Potential Locations forConfidentiality Attacks. • An attack can take place at any of the communications links. • The communications links can be: - Cable (telephone, twisted pair, coaxial cable, or optical fiber). - Microwave links. - Satellite channels.
Potential Locations forConfidentiality Attacks • Invasive taps or inductive taps are used to monitor electromagnetic emanation with both Twisted pair and Coaxial cables. • Neither type of tap is particularly useful with optical fiber. • Physically breaking the cable seriously degrades signal quality and it is therefore detectable.
Placement of Encryption Function • There are two major approaches to encryption placement: 1- Link encryption. 2- End-to-end encryption.
Key Distribution • For conventional encryption to work, the two parties to an exchange must share the same key, and that key must be protected from access by others. • Frequent key changes are required. • Therefore, the strength of cryptographic system relays on the key distribution technique.
Key Distribution • There are a number of ways to deliver the key: 1- Physical delivery between two parties A,B. 2- Third party physically delivered the key. 3- A and B use used key to encrypt the new key and transmit it to the other party. 4- Using an encrypted connection to third party, then the third party delivers a key on encrypted links to A and B.
A Key Distribution Scenario • One scenario to deploy the key distribution assumes that each user share a unique master key with the key distribution center (KDC). • Let us assume that user A wishes to establish a logical connection with B and require a one time session key to protect the data transmission over the connection. • A has a secret key ka, known only to itself and the KDC; similarly, B shares the master key kb with the KDC.
A Key Distribution Scenario • Steps: 1- A issues a request to the KDC for a session key, the message includes the identity of A and B and a unique identifier N1 for this transaction. 2- the KDC responds with a message encrypted using Ka, the message includes two items intended for A: - the one time session key Ks to be used for the session. - the original request message for matching.
A Key Distribution Scenario • Steps (Continue): And two items intended for B: - the one time session key, ks - An identifier of A IDA these two items are encrypted using kb 3- A stores the session key for use in the upcoming session and forwards to B the information that originated at the KDC for B.
A Key Distribution Scenario • Steps (Continue): • Because this information is encrypted with kb, it is protected. B now knows the session key ks , knows that the other party is A (from the IDA), and knows that the information originated at the KDC. • At this point, a session key has been securely delivered to A and B, and they may begin their protected exchange.
