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Security in Computing Chapter 2, Elementary Cryptography. Summary created by Kirk Scott. 1. Notation. S = Sender R = Recipient or Receiver T = Transmission Medium O = Outsider, possibly an Interceptor or Intruder. 2. Possible Attacks on Messages in Transition. A. Block the message
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wrr is a strong clue because it contains a double letter, and wr only reinforces this
If encryption was done by mono-alphabetic substitution, letter frequency analysis breaks the code
2. In the cryptographic arms race, you can essentially assume that anything encrypt is breakable
The book chooses to illustrate the idea behind Vernam with an example based on addition and modular arithmetic rather than XOR
The idea is that this is a system where the algorithm is extremely simple
Here is a little truth table showing that on a bit-wise basis, (p XOR q) XOR q = p:
Randomly guessing plaintext key pairs would have this kind of probability:
In any language, including English, some sequences are common and some are rare
This information comes from the Wikipedia article on differential cryptanalysis.
“In 1994, a member of the original IBM DES team, Don Coppersmith, published a paper stating that differential cryptanalysis was known to IBM as early as 1974, and that defending against differential cryptanalysis had been a design goal. According to author Steven Levy, IBM had discovered differential cryptanalysis on its own, and the NSA was apparently well aware of the technique. IBM kept some secrets, as Coppersmith explains: "After discussions with NSA, it was decided that disclosure of the design considerations would reveal the technique of differential cryptanalysis, a powerful technique that could be used against many ciphers. This in turn would weaken the competitive advantage the United States enjoyed over other countries in the field of cryptography." Within IBM, differential cryptanalysis was known as the "T-attack" or "Tickle attack".”
In order to be secure, the hashing algorithm or key has to be kept secret
X transmits trust to Y by performing and posting this transformation: D(KX PRIV, KY PUB)
A certificate consists of a full chain of individual “vouchers” that reaches the top of the hierarchy
At the lowest level, the message or contents of Z’s certificate become: