[정보보호, 암호론] 플레이페어 암호(Playfair Cipher): 1,2차 세계대전과 내셔널 트레져2

Playfair Cipher Explained by Kenny Lam

플레이페어 암호는 1차 세계대전과 2차 세계대전에서 사용된 암호입니다. 설명이 잘된 영상이 있어 담아둡니다.

History: It was used for tactical purposes by British forces in the Second Boer War and in World War I

and for the same purpose by the Australians and Germans during World War II.

@Wikipedia

플레이페어(Playfair Cipher)는 스코틀랜드의 과학자 라이온 플레이페어(Lyon Playfair)가 만들었으며 5by5 행렬을 사용합니다.

Encrypt: To encrypt a message, one would break the message into groups of 2 letters. If there is a dangling letter at the end, we add an X. For example. "Secret Message" becomes "SE CR ET ME SS AG EX". We now take each group and find them out on the table. Noticing the location of the two letters in the table, we apply the following rules, in order.

1. If both letters are the same, add an X between them. Encrypt the new pair, re-pair the remining letters and continue.

2. If the letters appear on the same row of your table, replace them with the letters to their immediate right respectively, wrapping around to the left side of the row if necessary. For example, using the table above, the letter pair GJ would be encoded as HF.

3. If the letters appear on the same column of your table, replace them with the letters immediately below, wrapping around to the top if necessary. For example, using the table above, the letter pair MD would be encoded as UG.

4. If the letters are on different rows and columns, replace them with the letters on the same row respectively but at the other pair of corners of the rectangle defined by the original pair. The order is important - the first letter of the pair should be replaced first. For example, using the table above, the letter pair EB would be encoded as WD.

Decrypt: To decipher, ignore rule 1. In rules 2 and 3 shift up and left instead of down and right. Rule 4 remains the same. Once you are done, drop any extra Xs that don't make sense in the final message and locate any missing Qs or any Is that should be Js.

이 암호는 영화 내셔널 트레져2에서 DEATH라는 암호키로 나오기도 했습니다.

  

Playfair Cipher