Now open Cryptool Online and navigate to Frequency Analysis. Copy the Ciphertext from the previous question. Change the 'Fragment Length' from 1 to 2 or 3. What do you notice about the frequency of 2 letter and 3 letter words?

Open this link: https://www.101computing.net/frequency-analysis/ 

In the Frequency Analysis text box, delete what's already there and paste the following text:

NM NU I MWAMT ASNGHWUIDDE IPJSXKDHBYHB, MTIM I UNSYDH OIS NS RXUUHUUNXS XV I YXXB VXWMASH OAUM CH NS KISM XV I KNVH.

TXKHGHW DNMMDH JSXKS MTH VHHDNSYU XW GNHKU XV UAPT I OIS OIE CH XS TNU VNWUM HSMHWNSY I SHNYTCXAWTXXB, MTNU MWAMT NU UX KHDD VNQHB NS MTH ONSBU XV MTH UAWWXASBNSY VIONDNHU, MTIM TH NU PXSUNBHWHB IU MTH WNYTMVAD RWXRHWME XV UXOH XSH XW XMTHW XV MTHNW BIAYTMHWU.

Click 'Start Frequency Analysis' and looking at the histogram provided, and the patterns of the texts (single letter words, two letter words, consecutive repeated letters), substitute letters and click 'start substitution'. You'll see the letter you've inputted as the key being substituted into the paragraph. What's the plaintext? 

Can you find an interesting application of cryptography and summarise how it is used?

Go to the 'Cryptool online' homepage and select 'Atbash Cipher'. Looking at the alphabet:

ABCDEFGHIJKLMNOPQRSTUVWXYZ

Insert a plaintext of your choice. Looking at the ciphertext that is displayed, and the alphabet shown above, can you define what the Altbash cipher is?

c) If the keyword of a Vigenère Cipher has repeated letters, does this make it any easier to break?

b) Given that the keyword length is less than 7, the third and fourth letters of the plaintext are F and O, respectively, and that A is a letter in the keyword, find the keyword and the plaintext.

The ciphertext JNHYSMCDJOP was obtained by encrypting an English word using a Vigenère Cipher:

a) The first and ninth letters of the plaintext are identical. What does this tell you about the key?

You want to encrypt the three-letter word "CAT" using a One-Time Pad. You and the recipient have already shared a secret key.

Plaintext: CAT

1. Convert Plaintext to Binary: First, convert the word "CAT" into its 8-bit binary ASCII representation.
   (Hint: The ASCII value for 'C' is 67, 'A' is 65, and 'T' is 84.)
2. Encrypt with XOR: Perform a bitwise XOR operation between the plaintext binary and the key to produce the ciphertext.
3. Input the Ciphertext into your answer box

Two spies, Alice and Bob, are lazy. They generate a 6-digit key K and use it to encrypt two different 6-letter messages before destroying it.

Alice's message (Plaintext 1 or P1): ATTACK

Calculate the Ciphertexts using the One-Time Pad approach.

Eve doesn't know the key K, but she suspects it was reused. She decides to subtract the two ciphertexts she intercepted (C1 - C2) for each position, taking the result modulo 26. Calculate this resulting sequence of numbers.