What is cryptography? Explain transposition cipher with an 5 example
Cryptography is the practice of secure communication in the presence of third parties. It involves the use of mathematical algorithms to transform plain text messages into encoded, unintelligible messages in order to prevent unauthorized access.
A transposition cipher is a type of cryptographic algorithm that rearranges the order of the letters or symbols in a message to create a new, scrambled message. This can be done by swapping the order of letters, shifting them across the message, or using a specific pattern to scramble the text. Here are five examples of transposition ciphers:
1. Rail Fence Cipher: The message is written in a zig-zag pattern across multiple rows and then read in a different order to create the encoded message. For example, the message "MEET ME AFTER SCHOOL" could be written as:
M . . . T . . . A . . . H . . . O . . .
. E . E . E . F . R . S . C . L . . .
. . T . . . M . . . E . . . O . . . L
The encoded message would be "MTAHOCERFSCLTEMOOL".
2. Columnar Transposition Cipher: The message is written in columns, and then the columns are rearranged according to a specific key. For example, if the key is "CAB", the message "ATTACK AT DAWN" would be written as:
A T A W N T K D A C
T C K A A A D T T
The encoded message would be "ATNKAATTACDTAW".
3. Route Cipher: The message is written in a spiral pattern on a grid, and then read off in a specific order to create the encoded message. For example, the message "NEVER GONNA GIVE YOU UP" could be written on a 4x4 grid as:
N E V E
R G O N
N A G I
V E Y O
Reading the message in a clockwise inward spiral starting from the top left corner would give the encoded message "NREVNAGIVOGUOEPY".
4. Scytale Cipher: The message is written along a long, thin rod (called a scytale), and then unwound to create the encoded message. For example, if the message "HELLO WORLD" is written on a scytale with a circumference of 5, the letters would be arranged as follows:
H L W
E O R
L D
L
The encoded message would be "HLLDLEOEORW".
5. Playfair Cipher: The message is written in a 5x5 grid with unique letters (excluding J) and then paired off into two letters. Using a specific set of rules, the letters are then swapped or shifted to create the encoded message. For example, the message "MEET YOU AT THE PARK" could be encoded as:
Plain text: ME ET YO UA TP AR KX
Encoded text: HN XK YT RU WL LS CZ
In this example, the "X" is used as a filler to make the number of letter pairs even. The rules for pairing the letters, exchanging them, and adding filler letters are specific to the Playfair Cipher.
Cryptography is the practice of secure communication by converting plaintext into ciphertext to protect the information from unauthorized access.
Transposition cipher is a type of encryption where the order of the letters in the plaintext is rearranged to form the ciphertext. It does not change the actual letters used, but only their positions. Here's an example of a transposition cipher:
1. Original Message: "HELLO WORLD"
2. Key: "31425"
3. Rearrange the letters of the original message based on the key:
- "H" stays in the first position.
- "E" moves to the third position.
- "L" moves to the fourth position.
- "L" moves to the second position.
- "O" moves to the fifth position.
- The space doesn't change its position.
- "W" moves to the first position.
- "O" moves to the third position.
- "R" moves to the fourth position.
- "L" moves to the second position.
- "D" moves to the fifth position.
4. Ciphertext: "HELOL WRODL"
In this example, the original message "HELLO WORLD" is encrypted into "HELOL WRODL" using the transposition cipher and the key "31425". To decrypt the ciphertext, the process is reversed by rearranging the letters back to their original positions based on the key.