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use of public and private keys

2.)Suppose there is a publicly readable file called /etc/public key. An entry in the file for user A consists of a user's identifier IDA, the user's public key, KUa, and the corresponding private key KRa. This private key is encrypted using DES with a key derived from the user's login password Pa. When A logs in the system decrypts Epa[KRa] to obtain KRa.
a.)The system then verifies that Pa was correctly supplied. How?
b.)How can an opponent attack this system?

Solution Preview

<br>1) The system decrypts the encrypted private key using the key derived from the login password.
<br>2) The system encrypts a random piece of text using the decrypted private key.
<br>3) The system decrypts this encrypted text using the public key.
<br>4) If the decrypted text matches ...

Solution Summary

The use of public and private keys are emphasized.