Caesar Cipher

Definition

Definition

The Caesar Cipher is a simple substitution cipher technique in cryptography. It involves shifting the letters of the alphabet by a fixed number of positions. It's named after Julius Caesar, who is reputed to have used it to communicate with his generals

Explanation

In the Caesar Cipher algorithm, a fixed number called the "key" or "shift" is chosen. This key determines how many positions each letter in the plaintext message is shifted. For instance, with a shift of 3, 'A' becomes 'D', 'B' becomes 'E', and so forth. The alphabet wraps around, meaning 'Z' becomes 'C'. Ultimately, the shifted letters constitute the ciphertext

Guidance

• Decide on a shift value, typically denoted by 'k'
• Iterate through each character in the plaintext message
• For each character
  • if it's a letter, shift it by 'k' positions
  • preserve uppercase/lowercase and handle wrapping around the alphabet
  • if it's not a letter, leave it unchanged
• Assemble the shifted characters to form the ciphertext

Tips

• remember to handle both uppercase and lowercase letters separately
• ensure the shift value is within the range 1-25 to avoid redundant shifts
• watch out for non-alphabetic characters in the plaintext and maintain their positions in the ciphertext

Practice

Practice

caesarCipher(plaintext, shift):
  ciphertext = ""
  for each character in plaintext:
    if character is an uppercase letter:
      shifted_char = (character + shift - 'A') % 26 + 'A'
    else if character is a lowercase letter:
      shifted_char = (character + shift - 'a') % 26 + 'a'
    else:
      shifted_char = character
    ciphertext += shifted_char
  return ciphertext

Solution

package main

func caesarCipher(text string, shift int) string {
    result := ""
    for _, char := range text {
        if char >= 'A' && char <= 'Z' {
            result += string((int(char-'A')+shift)%26 + 'A')
        } else if char >= 'a' && char <= 'z' {
            result += string((int(char-'a')+shift)%26 + 'a')
        } else {
            result += string(char)
        }
    }
    return result
}

public class CaesarCipher {

  public static String caesarCipher(String text, int shift) {
    StringBuilder result = new StringBuilder();
    for (char c : text.toCharArray()) {
      if (Character.isUpperCase(c)) {
        result.append((char) ((c + shift - 'A') % 26 + 'A'));
      } else if (Character.isLowerCase(c)) {
        result.append((char) ((c + shift - 'a') % 26 + 'a'));
      } else {
        result.append(c);
      }
    }
    return result.toString();
  }
}

function caesarCipher(text, shift) {
  return text.replace(/[a-zA-Z]/g, function (char) {
    const baseCharCode = char <= "Z" ? 65 : 97;
    return String.fromCharCode(
      ((char.charCodeAt(0) - baseCharCode + shift) % 26) + baseCharCode,
    );
  });
}

fun caesarCipher(text: String, shift: Int): String {
    return text.map { char ->
        when {
            char in 'A'..'Z' -> ((char - 'A' + shift) % 26 + 'A'.toInt()).toChar()
            char in 'a'..'z' -> ((char - 'a' + shift) % 26 + 'a'.toInt()).toChar()
            else -> char
        }
    }.joinToString("")
}

def caesar_cipher(text, shift):
    result = ""
    for char in text:
        if char.isalpha():
            base = ord('A') if char.isupper() else ord('a')
            result += chr((ord(char) - base + shift) % 26 + base)
        else:
            result += char
    return result

fn caesar_cipher(text: &str, shift: u8) -> String {
    text.chars()
        .map(|c| {
            if c.is_ascii_alphabetic() {
                let base = if c.is_ascii_uppercase() { b'A' } else { b'a' };
                ((c as u8 - base + shift) % 26 + base) as char
            } else {
                c
            }
        })
        .collect()
}

function caesarCipher(text: string, shift: number): string {
  return text.replace(/[a-zA-Z]/g, (char: string) => {
    const baseCharCode = char <= "Z" ? 65 : 97;
    return String.fromCharCode(
      ((char.charCodeAt(0) - baseCharCode + shift) % 26) + baseCharCode,
    );
  });
}