Question 1

Encrypt the message using polyalphabetic cipher, given key = 'codebreaker'. Note - you can use the VIGENERE table, which is given here. The tableu is an example of polyalphabetic cipher.

It was the threat of enemy interception that

Question 2

One way to avoid sharing the key is to use the autokey substitution cipher. A text-autokey uses the previous message text to determine the next element in the keystream (as you decrypt the text, you use the plain text as key).

Example:

Key: TEST

Encrypted Text: MSVTRWVTSMKWUC

The decrypted text is:

MSVT RWV TSMK WUC

TEST TODA

TODA

Decrypt the following cipher encrypted by Autokey cipher, given key = 'try'.

MYC VPT JMG VJD OWK QLC UHS JFQ TLV

HINT: You need to use the Vigenere tableau as a decryption toolso you should follow the opposite procedure of what you did in exercise 1.

Question 3

Find the plaintext and the key from the following cyphertext. You can use the tool at http://rumkin.com/tools/cipher/caesar.php (Links to an external site.)Links to an external site. to try different keys.

SHQQVWDWHXQLYHUVLWB

The Plaintext is:

The Key (number only (i.e. 45)) is:

Question 4

Encrypt the decrypted message using the keyword = 'GOOGLE' (Vigenere).

Table 2.3 The Modern Vigenre Tableau a A BCDEFGHIJK LMNOPQRSTUVWX Y Z C D E F G H?JKLMNOPQRSTUVWXYZA G HIJK LMN O P QRST UV W X Y Z ABC DEF H?JKI, M N O P Q R S T U v w X Y Z A B C D E F G IJ K L MN OP QR ST UVW X Y ZABCDEFG H JKLMNOPQRs.r ? v w X Y Z A B C D E F G H I KLMA N O P Q R S T U V W X Y Z A B C D E F G H I J L MNOPQR STUVWXYZABCDEFGHIJK m M NOP QRSTUVWX Y Z ABCDEFGH IJK L o O PQRSTUV W X Y Z ABCDEFGH IJK L M N p P QRS TU VWXY ZABCDEFGHK L MNO Q RSTUV W X Y Z ABC DEFGH I K L MNOP ,,T ? ? w X Y Z A B C D E F G H I J K L M N 0 P Q R T UVW X Y ZABC DE FGHIJKLMNO PQ R S U VWXYZ ABCDEF GHIJKLMNOPQ R S T X Y Z A B C D E F G H I J K L M N O P Q R S T U w W XY Z ABCDEFGHIJK LMNOPQRSTUV x X Y Z ABCDE FGHIJKLMNOPQRSTUV W y Y Z ABCDEF G HIJK LMN O P QR STUV W X : Z A B C DE F G HIJ K L M N O P Q R STUV W X Y