Fundamentals of Cryptography
1) Jason sends a message to Kristin using public key encryption.
a) What key will Jason use to encrypt the message?
b) What key will Kristin use to decrypt the message?
c) What key will Kristin use to encrypt the reply?
What key will Jason use to decrypt the reply?
Asymmetric Encryption his Private Key
2) What characteristics would make an encryption absolutely unbreakable? What characteristics would make an encryption impractical to break?
Classic encryption utilize ciphers to code plaintext into ciphertext using a secret coding and decoding process. The effectiveness of this process varies depending on the type and number of ciphers and the methods in which they are applied to the text. Unpredictable randomness makes an encryption absolutely unbreakable. This utilizes a onetime pad with each bit encrypted independently. A Block cipher with plaintext divided into blocks and an algorithm that produces blocks is impractical to break.
3) Does a substitution need to be a permutation of the plaintext symbols? Why or why not ?
No, substitution does not have to be a permutation of the plaintext symbols. This is because Cryptanalysis can be Ciphertext only. full or partial plaintext, cyphertext of any plaintext, algorithm and ciphertext or ciphertext and plaintext
4) Explain why the product of two relatively simple ciphers, such as a substitution and a transposition, can achieve a high degree of security.
Using the Diffusion Property a small change in plaintext produces an unpredictable change in ciphertext. When this is combined with a Confusion Property where a nearly correct key gives no indication of this it results in difficult exhaustive key searching so that two relatively simple ciphers can achieve a high degree of security.
5) If the useful life of DES was about 20 years (1977-1999), how long do you predict the useful life of AES to be? Justify your answer.
I predict it will be effective for 25 years. I am basing this upon the fact that it already is 12 years and AES still has not been evaluated in detail, It uses algorithms for security this provides computational efficiency, practical memory requirements, software suitability and flexibility. In order for AES to become ineffective computers capable of rapidly cycling though the permutations need to be readily available. Although this can occur quickly, the companies will be developing more complex ciphers as the potential hackers are breaking the lower level, less secure ciphers and algorithms. Many companies do not use the highest level of security available because the cost of applying the code is prohibitive for most communication. However, as processor speeds increase it reduces the cost of employing encryption codes. As that occurs the level of security increases throughout a system, thereby increasing exponentially, the effort needed to reach the most secure data.
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