INFA 640 Homework 2
Choose the best answer (one) and give reason in a few sentences for your choice or not choosing others. Please give a reference. To get full credit the reason should be in your own words, not a copy from any reference. Without reason in your own words you will not get full credit. The questions 1 thru 5 weigh 5 pts each. The sixth Question carries 25 pts. Please name your file as [lastname firstname INFA640_ HW2] Due last day of the session Sunday 7/22 11:59 PM pg. 1
a) Natural language letter frequency makes them easy to decode
b) Once you have the code book you can decode the message.
c) The number of letters in the alphabet makes them easy to decode.
d) Once the shift is determined the message is decoded almost instantly.
2) Claude Shannon presented the encryption design principles of _________________.
a) multiplication and factoring
b) exponentiation and Logarithms
c) confusion and diffusion
d) perplexion and reflection
Give reason how and why those help the encryption:
3) A good hash function creates _________ mapping between the source string and the output string.
b) as many as needed
d) one to one
Reason why is it a good function:
4) A number is relatively prime to another if they _____________.
a) have only each other as factors
b) have no prime factors in common
c) only have one prime factor in common
d) are both divisible by 7
5) Repudiation means
a) Faking one’s identity
c) Deny ownership
d) Plant clues in the text
6) (15 pts) The following is a ciphertext:
WSMODAMTSB, STARTKLIOH OL FGM AZGWM USGKOGWL EKGCFOFU AEML. OM’L AZGWM QTTHOFU BGWK MTAD YGEWLTR GF A UGAS AFR DGMOXAMTR MG RG MITOK ZTLM MG AEIOTXT OM, TLHTEOASSB CITF MIT LMAQTL AKT IOUI AFR MIT EGFLTJWTFETL KTASSB DAMMTK. OM OL AZGWM SABOFU MIT UKGWFRCGKQ YGK GMITKL’ LWEETLL, AFR MITF LMAFROFU ZAEQ AFR STMMOFU MITD LIOFT. EIKOL IARYOTSR
a) What kind of cipher text is this? Mono- or Poly alphabetic; [Hint: assume one and when that does not work look for the other] [1 points]
b) Describe your cryptanalysis process. List all the steps you went through to decrypt the message. The steps should be in sufficient details so that a reader would be able to decrypt the encrypted text without needing any help from you.
c) State the plain text message in readable form i.e. separating words if required
[the solution worked without the help from online tools will be given full credit]
[If you find solution online or use online tools and if you describe the steps by reverse engineering you will still get full credit]
[If you list partial steps you will get partial credit]
d) List features of the cipher- text that hindered and helped your decryption process. mention of helpful and hindering features [ 2 pts]
Note: Only a decrypted message even if it is correct one without the methodology and the detailed description of the self-explanatory steps used to decrypt, would not get points.