## bangor_boy

Hi I have been given a homework question asking to compare a made up Cipher along with know Ciphers, the cipher i have been given is called name cipher it takes the last letter of your first and second name and gives them a value and then adds them together an example would be Mac Apple = CE 3+5 = CE8. The algorithm for encrypting a plain text character at position n is simply to perform the XOR operation on the text with the key character using ^. So an example

C ^ C
O ^ E
N ^ 8
F ^ C
U ^ E
S ^ 8
E ^ C
D ^ E

How does this sound

The difference between this cipher and a verman cipher is that the verman cipher uses a random stream of data to XOR with plaintext. It isn't possible to use character frequency statistics to help crack the cipher as character frequency look for common pairs of letters for example "Th", "he" etc where in this cipher it is completely random which plain text letter gets XOR with the key so its impossible to match any letters.
It is possible to use brute force to crack the cipher as the bit size is quite low so wouldnt take that long to work out the cipher.
The name cipher would be stronger than Caesar cipher if the name cipher key is not known as the caesar cipher is very simple and just takes the user to work out how many places the letters have been shifted by.

Thanks

## Momerath 1,327

It is possible to use character frequency statistics to help crack the 'name' cipher. All you need to do is divide the encrypted text into three groupings (since we know the key is three characters long), determine the frequency of each group and XOR the highest frequency in each group with the most common value, which in English is the space character. This would, most likely, give us the original key which we can then use to decrypt the text.

If it doesn't give the key we can easily try the next most frequent letter, etc.

## bangor_boy

Cheers never looked at momerath in that way, what about the brute force and the Ceasar cipher

## Momerath 1,327

Ceasar cipher is easily broken with brute force as there are (in English, at least) only 25 possible keys. Even if you use a full 256 keys it's still (or even full 32 bit Unicode) trivial for modern computers.