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Classical Ciphers
Vernam Cipher

Vernam Cipher

Encrypt and decrypt text using the Vernam cipher, a classical XOR-based encryption method. Generate random keys or use your own key for encryption and decryption. Encrypted data is returned in Base64 format for safe storage and transfer.

Key

For best security, use a random key that is as long as the message and never reuse it.

Input
0 chars · 0 bytes
Try:
Result
✓ One-time pad scheme ✓ Key length must equal message length ✓ We never store your messages ✓ Processed on our server
Examples
Encrypt basic text
Key: KEY
Input HELLO
Output AwAVBwo=

Key: KEY. Encrypt mode applies XOR and outputs Base64.

Decrypt Base64 text
Key: KEY
Input AwAVBwo=
Output HELLO

Key: KEY. Decrypt mode decodes Base64 and applies XOR.

Unicode text example
Key: SECRET
Input Hello World
Output GyAvPip0BCoxPiE=

The tool supports UTF-8 text and can encrypt data from many languages and writing systems.

Different key, different result
Key: SECRET
Input HELLO
Output GwAPHgo=

Changing the key changes every XOR operation and produces completely different encrypted output.

How Vernam cipher works

The Vernam cipher encrypts data by applying the XOR (exclusive OR) operation between each byte of the message and the corresponding byte of a key. Because XOR is reversible, applying the same key again restores the original text.

In this tool, encrypted binary data is automatically encoded as Base64 so it can be copied, stored, and transferred safely as text. During decryption, Base64 is decoded first and then XOR is applied using the same key.

For maximum security, the key should be random, at least as long as the message, and used only once. When a shorter key is reused, the cipher still demonstrates XOR encryption but no longer provides the security guarantees of a true One-Time Pad.

The Vernam cipher is historically important because it introduced the XOR principle that later became the foundation of many modern stream cipher designs.

Vernam cipher vs One-Time Pad

The One-Time Pad (OTP) is a special case of the Vernam cipher. For perfect theoretical security, the key must be truly random, at least as long as the message, and never reused.

Most practical Vernam implementations, including educational tools, use reusable text keys. While this still demonstrates XOR-based encryption, it does not provide the unconditional security associated with a true One-Time Pad.

The warning shown by this tool helps identify situations where the key is reused or shorter than the message, which weakens security and removes the guarantees of an OTP.

History of the Vernam cipher

The cipher is named after Gilbert Vernam, an engineer who developed XOR-based encryption techniques for teleprinter communication in the early 20th century.

His work became one of the foundations of modern cryptography and inspired later stream ciphers and secure communication systems.

FAQ

Yes. Vernam decryption requires exactly the same key that was used during encryption.

XOR result is binary data. Base64 makes it safe to copy, store and transfer as text.

Yes. The tool works byte-wise with UTF-8 data, so it supports multilingual input.

XOR encryption combines message data and key data using the XOR operation. Applying the same key again reverses the process and restores the original message.

Security depends on the key. A true One-Time Pad with a random single-use key is theoretically unbreakable, while reusable keys can be vulnerable to cryptanalysis.

A key shorter than the message must be repeated during encryption. Reusing key material weakens security and removes the theoretical guarantees of a true One-Time Pad.

The XOR operation produces binary output that usually has no readable patterns. The tool displays this data as Base64 text for convenience.
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From the glossary
Keystream