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Lesson Objectives   Lesson Information   Slideshow   References   Questions

Lesson Objectives

1. Explain the difference between a block cipher and stream cipher and discuss types of each.
2. Illustrate and give real-world applications of secret key cryptography.
3. Discuss how encryption can be used to digitally sign a document.
4. Define certificates and explain their use in public key cryptography.
5. Explain Diffie-Hellman Key Exchange.
6. Explain the Shamir and Blakley secret sharing schemes.

Lesson Information

This lesson will look at a variety cryptographic techniques and constructs. It will begin by discussing different block and stream ciphers. The practical uses of secret key cryptography will also be discussed. Two examples are provided. A look at digital signatures will follow. At this point, certificates are defined. Certificates are used in public key cryptography to authenticate public keys. The Diffie-Hellman Key Exchange algorithm is provided. It is a secure way to establish a key between two people. Finally, the idea of secret sharing is presented. Two similar secret sharing schemes are then presented.

Slideshow

References

Crypto Applications, Tom Dunigan

Cryptography and Data Security, Peter Gutmann

Weird Attacks, Tom Dunigan

Questions

Listed below are a number of questions to assess your knowledge of the lesson objectives covered in this lesson. You can check your answers by scrolling down to the bottom of the document and checking the answer key.

1. (T/F) Stream ciphers are considered public key algorithms.
2. _________________ are fast and easy to implement, but they do not provide much security by themselves. This is why they are used as building blocks for more complex systems.
3. (T/F) It is not possible to forge a digital signature on a message.
4. A __________________ allows user's to retrieve other user's certificates or public keys.
5. (T/F) The Diffie-Hellman key exchange algorithm is able to set up a common key between Alice and Bob only if Lucifer is only able to eavesdrop.
6. (T/F) Secret sharing schemes allow n shares of a secret to be distributed, but require k of the shares to learn the original secret.
7. ___________ is a perfectly secure secret sharing scheme. In other words, no information is learned about the secret until the required number of shares are assembled.
8. (T/F) Using an Electronic Code Book, if two of the same plaintexts are passed through the algorithm will produce different ciphertexts.
9. For Alice to compute the digitial signatue of a message M, she uses her __________ key to encrypt the message.
10. For Bob to check the digital signaute of message M to verify that it came from Alice, Bob learns Alices's ____________ key and decrypts the signature and compares it to the message.
11. (T/F) Using Blakley's Secret Sharing Scheme, if k of n shares are needed to recover the secret, then k-1 shares know more about the secret then k-2 shares.

Answer Key

1. The answer to question 1 is False.
2. The answer to question 2 is Linear Feedback Shift Register.
3. The answer to question 3 is False.
4. The answer to question 4 is Certificate Authority.
5. The answer to question 5 is True.
6. The answer to question 6 is True.
7. The answer to question 7 is Shamir Secret Sharing.
8. The answer to question 8 is False.
9. The answer to question 9 is Private or Secret.
10. The answer to question 10 is Public.
11. The answer to question 11 is True.

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