Cryptanalysis

1. Cryptanalysis codes & ciphers

2. Transposition • Spacing • alter or eliminate spacing • the simplest transposition • Mirror writing • reverse words or write the entire message backward • Switching letters • Pig Latin is an example.

3. Transposition • Rail fence • alternate writing on 2 or 3 lines • the ciphertext is written horizontally

4. Rail fence W E C R E R D S O E E A I V D W E C R E R D S O E E A I V D Plaintext: WE ARE DISCOVERED Ciphertext: WECRERDSOEEAIVD

5. Transposition • Inside-out cipher • find the middle letter (or letters) in each word • write words (or the entire message) inside-out • different ways of doing this • Example: MISTY becomes SITMY, COOPER becomes OPOECR • Example: JESSE becomes EJSES, STRIPE becomes RTSEPI

6. Transposition • Geometric ciphers • To decipher the message, the recipient must have a copy of the original shape and know the direction of transposition. • A keyword is also needed for some transpositions.

7. Plaintext: Proceed to Philadelphia…

8. Plaintext: Peace can be achieved when it is built upon vigilance and strength. Keyword: diplomatics The ciphertext is created by removing the letters from each vertical column, in alphabetical order of the keyword. The ciphertext shown below has been put into blocks of 5 letters each.

9. Plaintext: Peace can be achieved when it is built upon vigilance and strength. Keyword: diplomatics The ciphertext is created by removing the letters from each diagonal going to the right, in alphabetical order of the keyword. The ciphertext shown below has been put into blocks of 5 letters each.

10. Transposition • Route cipher • Create a row x column matrix • Write the text of the message, following a particular pattern • The ciphertext is created by reading across rows from left to right, top to bottom • Recipient needs to know the dimensions of the matrix • Describe the correct path needed to read the message

11. Transposition • Columnar transposition • The message is written out in rows of defined length, creating a matrix • The ciphertext is created by going down the columns, in alphabetical order of a keyword • Nulls can be used to fill up columns • In irregular columnar transposition, nulls are not used. • The recipient needs to know the keyword. Dividing the message by the number of letters in the keyword gives the length of each column. • To read the message, write the letters down the columns and put them back in keyword (not alphabetical) order.

12. Transposition • Double columnar transposition • The message is written in rows, as for columnar transposition • Rearrange columns in alphabetical order of the keyword • Finally, read off rows in alphabetical order of the keyword (can be the same or a different keyword) • Myszkowski transposition • A special type of columnar transposition that uses a keyword with repeated letters • Read differently than usual

13. Transposition • Disrupted transposition • Crossword puzzle • Grille • Turning grille

14. Other Transposition Ciphers • Popsicle stick cipher • line up letters with marks on a popsicle stick • fill in the rest of the space with nonsense • each word on a separate line

15. Other Transposition Ciphers • Zombie cipher • random alphabet is used as encoding strip • write the first letter of message under A, and proceed from there, continuing onto the next row as needed • recipient needs a copy of the encoding strip to make sense of the message