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Security. Cryptography (1). Intruders and eavesdroppers in communication. Cryptosystems. Symmetric key cryptosystems Same key is used for encryption and decryption DES Asymmetric key cryptosystems Public key and private key Usage depends on application RSA Hash functions
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Cryptography (1) • Intruders and eavesdroppers in communication.
Cryptosystems • Symmetric key cryptosystems • Same key is used for encryption and decryption • DES • Asymmetric key cryptosystems • Public key and private key • Usage depends on application • RSA • Hash functions • Detecting message tampering • MD5
Authentication • Authentication based on a shared secret key.
Efficient Authentication? • Authentication based on a shared secret key, but using three instead of five messages.
Authentication Using Public-Key Cryptography • Mutual authentication in a public-key cryptosystem.
Authentication Using a Key Distribution Center (1) • Figure 9-15. The principle of using a KDC.
Authentication Using a Key Distribution Center (2) • Figure 9-16. Using a ticket and letting Alice set up a connection to Bob.