Activity I

Symmetric Encryption

Symmetric encryption is the process of encoding and decoding messages using the same key. An important aspect of this type encryption is to ensure that the key is not compromised and that only the sender and receiver have access to the key used to modify the plain text.

Substitution is one technique used in symmetric encryption. The first part of this activity is intended to illustrate symmetric encryption using substitution. The second part of this activity illustrates the block cipher technique using a product technique that emulates the Feistel structure with substitution and transposition.

Work together in pairs on this activity. One class time will be devoted to this activity.

Part One

1. A file explaining the Special Forces symmetric substitution cipher is located in the Content Section of Blackboard. Use this technique for this exercise. Make sure you show all your work.
2. Using the two keys (memory words): cryptanalysis and network cryptology, encrypt the following message:
a. Be at the third pillar from the left outside the lyceum theater tonight at seven. If you are distrustful bring two friends.
b. You may make reasonable assumptions about how to treat redundant letters and excess letters in the memory words and how to treat spaces and punctuation. Identify your assumptions in you summary.
3. Decrypt the ciphertext to show the original message.
4. What are the advantages and disadvantages of using this technique? Would this technique have any merit in today's technology rich environment?

Part Two

1. A file explaining the Tiny Encryption Algorithm (TEA) which is a Feistel Block Cipher method is located in the Content Section of Blackboard. Use this technique for this exercise. Make sure you show all your work.
2. TEA operates on 64-bit blocks of plaintext using a 128 bit key. The plaintext is divided into two 32 bit blocks (L0, R0), and the key is divided into four 32 bit blocks (K0, K1, K2, K3). Encryption involves repeated application of a pair of rounds, defined as follows for rounds i and i + 1:

Li = Ri-1
Ri = Li-1 + F(Ri-1, K0, K1, δi)
Li+1 = Ri
Ri+1 = Li + F(Ri-1, K2, K3, δi+1)

where F (M, Kj, Kk, δi) = ((M<< 4) + Kj) + ((M>> 5) ) + Kk) + (M + δ1)
and where the logical shift of x by y bits is denoted by x<> y, and δi is a sequence of predetermined constants.

3. Using the TEA concept, but limiting the plaintext block to 16 bits and the key block to 32 bits, complete the following block cipher given the following plaintext message and key, respectively (in hexadecimal): A2B9H and 4C8AF6B9. Use B3H for δ.
4. Illustrate the operation of TEA using a block diagram or flow chart. Complete the first four rounds of iterations. Show the output values for Li and Ri for each of the rounds (Round 1, Round 2, Round 3, Round 4).
Deliverable Items

Theory or Principle Illustrated:

The description should include any mathematical analysis, results, or truth tables, as appropriate. All mathematical analyses must use the equation editor. All simulation results, and tables must be electronically generated and merged into the document text. This section develops the expected values of the activity. There should be a one to one correlation between the Part 1 and Part 2 "Procedure Steps" and the "Theory or Principle Illustrated" sections.

Experimental Data and Presentation:

This section is the recording and presentation of the data. This includes tables, charts, etc. Each step in the procedure that requires a measurement or observation should have a corresponding entry in this section. It may be necessary to record observations in tables to facilitate readability. Measurement values may need to be presented in table and graph format to facilitate the evaluation of the information. It is acceptable to include any error analysis along with the measured and theoretical or simulation data in this section. The procedure step should be referenced with the measurement value or observation. All information must be electronically generated and merged into the document text.

Discussion of Results:

This section is a detailed discussion of the results of the experiment. Each step in the procedure that requires a measurement or observation should have a corresponding discussion in this section. Discussions should include analysis and a comparison of the results with the expected value from the "Theory or Principle Illustrated" section. Explain differences between the actual and expected results here. It is acceptable to reference other sections of the report, namely the "Theory or Principle Illustrated", "Experimental Data and Results", and "Procedure" sections. Details of all tests performed including % error relative to the expected values are required. In addition, a conclusion relative to the purpose based on the comparison of actual test data to expected values is required.

CONDITIONS:

Given a pencil, paper, two memory 10-letter word(s) or phrases, in d classroom or field environment, under unconventional warfare (UW) conditions.

STANDARD:

Write a message using a double transposition cipher in 10 minutes without error.
PERFORMANCE MEASURES:

1. Write a message using a single transposition cipher in 5 minutes without error.
a. Write the first 10-letter memory word(3) or phrase across the paper.

NOTE: Leave enough space between the letters of the memory word to avoid confusion when writing the clear text message underneath.

b. Write the message underneath the 10 letters; place the eleventh letter of the message under the first letter of the message and continue writing on a letter-by-letter basis until the message is complete. Put Us at the ends of sentences and end of message to insure each letter of memory phrase has an equal number of letters underneath.

c. Alphabetize the first 10-letter memory word(s) or phrase. Put small numbers above each letter. For example A is 1, B is 2, C is 3, Z is 10.

d. Draw lines vertically separating the 10-letter memory word(s)/phrase. Extend these lines down the page until the bottom line of the message is reached.

e. Go to column number 1 and write down the first five letters in that column forming a 5-letter group.

f. If the letters in column 1 do not make a 5-letter group, go on to ooluen 2, and finish the group. (Always start at the top of the column and work down).g. If the letters in column 2 do not complete the 5-letter group, go on to column 3 and finish the group.

h. Continue this process until all letters are placed into 5-letter groups.
i. Put the 5-letter groups in order from left to right as if reading a page. (See fig 1.)

2. Write a message using a double transposition cipher in S minutes without error.
a. Write the second memory word(s)/phrase on the paper.

2 8 8 7 4 8 1 S 3 10
CORNFLAKES
SEND R E S U P P
L Y T O T illi I
DOER Y T HECK
UR CH X X AMMO
NEEDEDURCE
N T L Y W I T H MA

C A Z 1 N E S X

b. Place the first 5-letter group of the single transposition cipher underneath the first five letters of the second memory word(s)/phrase on a letter-by-letter basis.

c. Place the second 5-letter group of single transposition cipher under the second five letters of the memory word(s)/phrase.

d. Place the third 5-letter group of single transposition cipher under the first 5-letter group of single transposition cipher on a letter-by-letter basis.

e. Continue on until all 5-letter groups of single transposition cipher are placed under the second memory word(s)/phrase on a letter-by-letter basis.