Cryptography: Caesar Cipher and Modulo Operator| Encryption and Decryption

Summary

In this video, the presenter introduces the basics of cryptography, explaining key concepts such as encryption, decryption, and cryptographic methods. The term 'cryptography' originates from Greek words meaning 'hidden writing'. The video covers two main techniques: the shift cipher, where letters are shifted by a fixed number, and the modulo operator, which uses mathematical operations to encrypt and decrypt messages. The presenter demonstrates these methods with examples, showing how letters in a word like 'mathematics' or 'power' are transformed into cipher text. The video concludes with an invitation to subscribe for more educational content.

Takeaways

• 😀 Cryptography comes from two Greek words: 'crypto' meaning hidden and 'graphene' meaning writing.
• 😀 Encryption is the process of transforming plaintext into coded text using an algorithm.
• 😀 Decryption is the reverse of encryption, converting coded messages back to plaintext.
• 😀 A key is a string of information used to unlock encrypted messages and make them readable.
• 😀 The Shift Cipher (Caesar Cipher) shifts letters in the alphabet by a specified number.
• 😀 In the Shift Cipher, the direction of the shift can either be to the left or right.
• 😀 Using a Shift Cipher with a shift of 3, 'mathematics' becomes 'wkhpdwdlfv'.
• 😀 The Modulo Operator method involves converting letters to numbers (a=0, b=1, etc.) and applying arithmetic to encrypt and decrypt messages.
• 😀 In Modulo encryption, you add the key value to the number corresponding to each letter and apply modulo 26 to handle overflow.
• 😀 To decrypt using the Modulo method, you subtract the key value from the number corresponding to each letter.
• 😀 An example of Modulo encryption with a key of 5 is the word 'power', which becomes 'tsbjw'.

Q & A

What is cryptography?

Cryptography is the practice of transforming readable data into an unreadable format to secure its confidentiality. The term originates from two Greek words: 'crypto,' meaning hidden, and 'graphene,' meaning writing.

What are the key terms in cryptography?

The key terms in cryptography include 'encryption,' which is the process of converting plain text into a coded format, and 'decryption,' which is the process of converting the coded message back into readable form. A 'key' is also a term used, referring to the string of information that helps reveal the encrypted message.

What is encryption?

Encryption is the process of transforming plain text into code using an algorithm, making it unreadable to unauthorized parties.

What is decryption?

Decryption is the reverse of encryption, where the encrypted code is converted back into plain text, making it readable again.

What is the shift cipher (also known as the Caesar cipher)?

The shift cipher, or Caesar cipher, is a simple type of substitution cipher where each letter in the plaintext is shifted by a certain number of positions in the alphabet. For example, shifting by 3 turns 'A' into 'D.'

How do you encrypt the word 'mathematics' using a shift cipher with a shift of 3?

To encrypt the word 'mathematics' with a shift of 3 to the right, you shift each letter three positions forward in the alphabet: M becomes P, A becomes D, T becomes W, and so on, resulting in the encrypted message 'WKHDWLV.'

What is the modulo operator in cryptography?

The modulo operator in cryptography involves converting each letter to a corresponding number (A = 0, B = 1, ..., Z = 25) and then adding the key value to that number. If the result exceeds 25, it wraps around to the beginning of the alphabet.

How do you encrypt the word 'power' using the modulo operator with a key value of 5?

To encrypt 'power' using a key value of 5, convert each letter to its corresponding number (P = 15, O = 14, etc.). Add 5 to each number and convert it back to letters, resulting in 'Uwtja.'

How do you decrypt a message encrypted with the modulo operator?

To decrypt a message encrypted with the modulo operator, subtract the key value from each number corresponding to the letter. If the result is negative, wrap around starting from Z and counting backward.

What happens if the result of a modulo operation is greater than 25 or negative?

If the result of a modulo operation exceeds 25, it wraps around to the beginning of the alphabet. If the result is negative, it starts from the end of the alphabet (Z) and counts backward.