** Cryptography, Computer Science**

- Chapter 1. Classical Cryptosystems
- Explain the Index of Coincidence (IOC).
- Why does the One Time Pad have
*Perfect Secrecy*?

- Chapter 4: Cryptographic Hash Functions
- What is a message digest?
- Most cryptographic hash functions are designed to take a string of any length and convert it to a _________ length string.
- Cryptographic hash functions are ____________ to collisions.

- Chapter 6: Discrete logs
- Describe the ElGamal Discrete Log Cryptosystem.
- What are the three algorithms used to solve for the discrete log?
- Referring to Crypto System 6.1, the value of p should have at least _____ digits in order to thwart known attacks.

- Diffie-Helman
- Describe the Diffie-Hellman key exchange method. Hint – read the Wiki article. Diffie-Hellman key exchange is not in the text in an explanatory form. Show the basic math behind it.

- Chapter 7: digital Signature Schemes
- What are the six attacks on digital signature security?
- Refer to page 283, CS 7.1. Suppose Alice’s RSA modulus is m = 91, her encryption exponent is e = 7 and her decryption exponent is d = 31.
- Alice wants to sign the message x = 21. Calculate her signature.
- Bob receives a message-signature pair from Alice (not related to the above) and decrypts it, and gets (x=89, y=54). Does he regard the pair as likely to be authentic, or does he know that the pair has been altered? Show your work.

- Pseudo Random Number/Bit Generators
- Explain how the Blum-Blum-Shub (BBS) generator works.
- For Example 8.4, page 337, reproduce the first two outputs 143135 and 177671 (after i = 0, 20749), in table 8.3. Show your work.

Please answer according to the text book below

http://www.icst.pku.edu.cn/course/Cryptography/CryptographyTheoryandpractice%283ed%29.pdf

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