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Caesar Cipher Program in Java

Last Updated on May 22, 2023 by Prepbytes

In this article, we will dive into the fascinating world of encryption and guide you through the process of building your own Caesar Cipher program in Java. Whether you’re a beginner seeking an introduction to encryption or an experienced developer looking to enhance your Java programming skills, this article will provide you with a comprehensive foundation to understand and implement the Caesar Cipher.

By the end of this article, you will have not only built your own Caesar Cipher program in Java but also gained a deeper understanding of encryption techniques and their practical applications. Armed with this knowledge, you will be well-prepared to tackle more complex encryption algorithms and contribute to the ever-evolving field of cybersecurity.

What is Caesar Cipher?

Caesar Cypher is a fascinating problem that dates back to the time of Julius Caesar, when information was transmitted by changing the original message in a way similar to how the encryption-decryption phenomenon is used today, as off-topic as that may appear at first.

If character B needs to be shifted by three positions, then B->C->D->E can define the transition nicely. Encryption is achieved by acquiring the shift input, n, then shifting each character in the string by n places.

Decryption of character is the process of translating a character back to its unencrypted form, which is B. To qualify as a Caesar Cypher, this method of substitution is applied to each word’s character.

The shift value and modulo can be added together to find values that are more than the unit value of the highest alphabet, z, which is 26 according to the two formulas below.

Dry Run of Caesar Cipher Program in Java

We can now see more clearly whether or not the Caesar cypher genuinely functions. Let’s walk through an example step by step to learn how it operates.

Our task is to first encrypt and then decrypt the input word, ATLAS, returning it to its original form. We can accomplish this using the detailed technique shown and discussed below.

In the above illustration, A was moved by three places and placed as D in the result string.

The alteration made of T with change of +3 in 1st index will lead to storage of V in the string.

At index 2, L was replaced with O, that is stored in the 2nd index of result string.

Similar to the operation at the 0th index, here also, A is going to turn into D when shifted by 3 positions. Thus D is going to be stored in the resultant string.

The final operation on the last index to replace S in a similar fashion, leads to V getting stored in the result string.

Algorithm of Caesar Cipher Program in Java

We talked about utilizing the shifting integer to replace character values on every character stored in the string in the previous section. Let’s now examine what would be a clear algorithm to reinforce our understanding of the Java Caesar cypher program.


  1. Take a shifting integer between the ranges of 1 and 25, and a string.
  2. Make a fresh result string.
  3. For every character in the string, iterate:
    • Depending on whether the character is being encrypted or decrypted, shift it by n places and store it as char type, newchar.
    • Include newchar, the shifted character, in the result string.
  4. Return the string or print it.

Code for Caesar Cipher Program In Java

Let’s move on to the code element of this Java Caesar cypher program once we have a good knowledge of how each phase in the process plays out.

class CaesarCipher {

    public static StringBuffer encrypt(String plaintext, int shift) {
        StringBuffer result = new StringBuffer();
        for (int i = 0; i < plaintext.length(); i++) {
            if (Character.isUpperCase(plaintext.charAt(i))) {
                char ch = (char)(((int)plaintext.charAt(i) +
                                  shift - 65) % 26 + 65);
            } else {
                char ch = (char)(((int)plaintext.charAt(i) +
                                  shift - 97) % 26 + 97);
        return result;
    public static void main(String[] args) {
        String plaintext = "ATLAS";
        int shift = 3;
        System.out.println("Plaintext  : " + plaintext + "\n");
        System.out.println("Shift : " + shift + "\n");
        System.out.println("Ciphertext: " + encrypt(plaintext, shift));

Explanation: The plain text string and shift integer are obtained from the user and sent to the encrypt method in the driver code, where the result is declared and stored in a StringBuffer().

Each character in the plaintext is subject to the condition, with shifting carried out inside the program’s loop. In order to print the outcome, we finally return the result to the main function.
k to the main function to print the result.


Plaintext  : ATLAS

Shift : 3

Ciphertext: DWODV

Analysis of Caesar Cipher Program in Java

In terms of the study of the code for the Java Caesar cypher program, it is clear from the logic that we will traverse each character to change the value for encryption; as a result, the code will, at worst, be linear in complexity. The time complexity is therefore written as O(N).

In terms of space complexity, we’ll be storing the string in a stringBuffer that can accommodate up to N values. As a result, the complexity of the auxiliary space is often O(N).

By implementing the Caesar Cipher in Java, you have gained a solid understanding of string and character manipulation, as well as the use of loops for iterative processes. This hands-on experience will not only enhance your Java programming skills but also serve as a stepping stone to explore more advanced encryption techniques.

Remember that the Caesar Cipher is a relatively simple encryption method, and while it provides a great starting point, it has certain vulnerabilities. As you progress in your journey, you may want to explore more robust and secure encryption algorithms, such as the Advanced Encryption Standard (AES) or the Rivest Cipher (RC4).

Additionally, you can further extend your program by incorporating features such as input validation, handling special characters, or implementing a user-friendly interface. The possibilities are endless, and with each enhancement, your skills as a programmer and your understanding of encryption will continue to grow.


Q1. Why is the Caesar Cipher considered a weak encryption method?
Ans. The Caesar Cipher is considered weak because it has a limited key space of only 26 possible shifts. Additionally, it is vulnerable to frequency analysis attacks, where an attacker can analyze the occurrence of letters in the cipher text to deduce the key and decrypt the message.

Q2. Is the Caesar Cipher still used today?
Ans. The Caesar Cipher itself is no longer widely used for secure communication due to its vulnerabilities. However, it serves as a foundational concept in the study of encryption and cryptography. Modern encryption algorithms build upon more complex mathematical principles and advanced techniques.

Q3. Can I use the Caesar Cipher to encrypt messages in other languages besides English?
Ans. Yes, the Caesar Cipher can be used to encrypt messages in any language that uses an alphabet. However, keep in mind that the shift value must be adjusted according to the specific language’s alphabet size and letter frequency.

Q4. How can I decrypt a message encrypted with the Caesar Cipher if I don’t know the shift value?
Ans. If you don’t know the shift value, you can perform a brute-force attack by trying all possible shift values and examining the decrypted messages. However, this method is only practical for small text lengths, as the number of possibilities increases with the length of the message.

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