Tugas 1 - Keamanan Jaringan

Summary

In this video, the speaker introduces two classic encryption methods: Transposition Cipher and Progressive Caesar Cipher. The Transposition Cipher works by rearranging letters in a grid, reading vertically to create the encrypted message. The Progressive Caesar Cipher, a variation of the Caesar Cipher, shifts each letter progressively with increasing values (e.g., +3, +5, +7). Decryption for both ciphers involves reversing the process. The video also touches on techniques for dealing with unknown shifts and encrypting numbers, demonstrating practical examples for each method to enhance understanding.

Takeaways

• 😀 Cipher is a traditional method of encryption and decryption used historically to protect messages and texts.
• 😀 The Transposition Cipher (Scissor Box Cipher) involves writing the message into a grid and then reading it column by column to encrypt it.
• 😀 To use the Transposition Cipher, if the message length doesn’t fit a perfect grid, padding (such as 'X') is added to fill the grid.
• 😀 The encrypted text in Transposition Cipher is generated by reading the grid columns vertically (top to bottom).
• 😀 Decryption in the Transposition Cipher involves reversing the process, reading the encrypted message from top to bottom and then re-assembling it row by row.
• 😀 Progressive Shift Cipher increases the shift value progressively for each character in the message (e.g., +3 for the first letter, +5 for the second, etc.).
• 😀 In Progressive Shift Cipher, to encrypt a message, each letter is shifted by an increasing value based on its position in the message.
• 😀 Decryption of Progressive Shift Cipher involves reversing the shift, subtracting progressively larger values from each character.
• 😀 Numbers in ciphers, particularly Progressive Shift, are handled digit by digit, with each digit shifted individually using a modular operation.
• 😀 In case the shift pattern is unknown, techniques such as Frequency Analysis or Machine Learning can be used to deduce the correct shift values.
• 😀 For number encryption in Progressive Shift Cipher, each digit is shifted separately, and the formula used is (Old number + Shift) mod 10.

Q & A

What is a cipher, and how is it used in encryption and decryption?

A cipher is a traditional method of encryption and decryption used to protect messages or text. It has been historically used to secure communication by transforming readable text into an unreadable format and vice versa.

What is the difference between a transposition cipher and a substitution cipher?

A transposition cipher rearranges the letters of the plaintext according to a specific pattern, while a substitution cipher replaces the letters with other letters or symbols based on a defined rule.

How does a transposition cipher work?

In a transposition cipher, the plaintext is written into a grid, and the characters are read in a specific pattern to generate the ciphertext. For example, the characters can be read column-wise after filling the grid row by row.

What is the role of padding characters in a transposition cipher?

Padding characters, like 'X', are added when the length of the message does not perfectly fit the grid dimensions. These extra characters fill empty spaces to ensure the grid is completely filled.

How does decryption work in a transposition cipher?

To decrypt a transposition cipher, the encrypted message is written in columns, and the message is read row by row. This process reverses the encryption method, recovering the original plaintext.

What is a progressive cipher?

A progressive cipher is a variant of the Caesar cipher where the shift value increases progressively with each character. For example, the first letter is shifted by 3, the next by 5, the next by 7, and so on.

How is encryption performed using a progressive cipher?

In a progressive cipher, the shift value starts from a defined number and increases progressively with each character. For instance, the first letter is shifted by 3, the second by 5, and the third by 7, continuing the pattern.

What happens if the shift value is unknown in a progressive cipher?

If the shift value is unknown, statistical analysis can be used to guess the shift pattern. One approach is to analyze letter frequencies or use machine learning techniques to predict the correct shifts.

How does decryption work in a progressive cipher?

To decrypt a message encrypted with a progressive cipher, the reverse shifts are applied. For example, the first letter is shifted backward by 3, the second by 5, and so on, until the original message is restored.

How are numbers encrypted using a progressive cipher?

For numbers, each digit is treated separately. The digits are shifted according to the defined pattern, and the encryption is done for each individual number. For example, 5 becomes 9, 0 becomes 6, etc., when applying the shifts.