Information Security Assignment Questions

ASSIGNMENT QUESTIONS-1

1. A sends a message to B in the encrypted format. What type of attack is possible in this scenario? 2. Using this Playfair matrix M F U N Z V E L D S encrypt this message: “mustseeyou”

H O W A T

I/J P X R B

K Q Y G C

3. Encrypt the message "meet me" using the Hill cipher with the key (

).

4. Using the Vigenère cipher, encrypt the word "explanation" using the key “leg”.

5. This problem explores the use of a one-time pad version of the Vigenère cipher. In this scheme, the key is a stream of random numbers between 0 and 26. For example, if the key is 3 19 5 ..., then the first letter of plaintext is encrypted with a shift of 3 letters, the second with a shift of 19 letters, the third with a shift of 5 letters, and so on. Encrypt the plaintext “sendmoremoney” with the key stream 9 0 1 7 23 15 21 14 11 11 2 8 9. 6. Using Rail fence technique, encrypt the plain text “postponeattacktilllnotice” using 3 rows.

7. What are the differences between DES and AES? 8. Decipher the message YITJP GWJOW FAQTQ XCSMA ETSQU SQAPU SQGKC PQTYJ using the Hill cipher with the inverse key 9. Encrypt using RSA algorithm : p = 3; q = 11, e = 7; M = 5 10. Calculate x and gcd(40,65) using extended Euclidean algorithm:

ANSWER KEYS

1. Traffic Analysis 2. Plain Text : MUST SEE YOU Cipher Text : UZ TB LD GZ PN 3. Plain Text : MEET ME Enciphering Matrix : (

)

Plain Text Vectors : (

)(

Cipher Text Vectors : ( (

)(

)

) (

)

)

(

)

(

( (

) )

) ( ( (

)

(

) (

)

) )

GVUIGV 4. PBVWETLXOZR 5. BEOKJDMSXZPMH 6. PTNTCINI OPETKLOC SOAATLTE 7. DES

AES

Stream cipher

Block cipher

Message 64 bit long

Message 128 bit long

No: of rounds = 16

No: of rounds = 10/12/14

Key length = 64 bits

Key length = 128/192/256 (depending on no: of rounds)

No: of S-boxes = 8

No: of S-boxes = 1

Key expansion produces 16 48-bit keys

Key expansion produces 44 128-bit keys

Look

up

tables

used

are:

Initial Look up table used is one S-box

permutation table, permuted choice 1, permuted

choice

2,

inverse

initial

permutation table, expansion permutation

table and S-boxes Other operations used are: XOR and left- Other shift operations

operations

substitution,

used

shifting

are:

rows,

bytemixing

columns, left circular rotation and XOR operation

8. Cipher Text : YITJP GWJOW FAQTQ XCSMA ETSQU SQAPU SQGKC PQTYJ Plain Text : DIFFICULTIES ARE THINGS THAT SHOW WHAT MEN ARE P 9. n = p*q n= 3*11=33 f(n) = (p-1)*(q-1) = 2*10 = 20 e=7 7*d = 1 (mod 20) => d = 3 PU = {7,33} PR = {3,33} M=5

10. 40*x = 1 (mod 65) Calculating GCD: 65 = 40(1) + 25 40 = 25(1) + 15 25 = 15(1) + 10 15 = 10(1) + 5 10 = 5(2) + 0 GCD = 5

Calculating x: 5 = 15 – 10(1) 5 = 15 – [25 – 15(1)](1) 5 = 15(2) – 25(1) 5 = [40 – 25(1)](2) – 25(1)

5 = 40(2) – 25(3) 5 = 40(2) – [65 – 40(1)](3) 5 = 40(5) – 65(3) X=5