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Beaufort Cipher

Beaufort Cipher

Encrypt and decrypt text with the Beaufort cipher online using a keyword and selectable alphabet. A classical polyalphabetic cipher where the same operation can be used for both encryption and decryption.

Input
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Result
✓ Polyalphabetic substitution cipher ✓ Same key encrypts and decrypts ✓ We never store your messages ✓ Processed on our server
Examples
Encrypt with the keyword FORT Key: FORT
Input DEFEND THE EAST WALL
Output CKMPSL YMB KRBM SRIU

Keyword: FORT. The repeating keyword is applied to each letter while spaces are preserved unchanged.

Decrypt with the same keyword Key: FORT
Input CKMPSL YMB KRBM SRIU
Output DEFEND THE EAST WALL

Keyword: FORT. Beaufort is reciprocal, so applying the same transformation again restores the original message.

Keyword encryption on a short message Key: FORT
Input HELLO WORLD
Output YKGIR SDCUL

Keyword: FORT. Each plaintext letter is transformed using the current keyword letter, then the keyword repeats.

Preserve spaces, numbers, and punctuation Key: FORT
Input MEET AT 9 PM!
Output TKNA FV 9 CH!

Keyword: FORT. Only letters are transformed; spaces, punctuation marks, numbers, and other symbols remain unchanged.

How the Beaufort cipher works

The Beaufort cipher is a classical polyalphabetic substitution cipher that uses a repeating keyword to transform text. Unlike the Vigenere cipher, each output letter is calculated from the key letter and the plaintext letter using a reversed relationship.

The most distinctive feature of the Beaufort cipher is its reciprocal nature. The same transformation is used for both encryption and decryption, which means the same keyword can process text in either direction.

Because the cipher changes substitutions based on the current key letter, it is more resistant to simple frequency analysis than monoalphabetic ciphers such as Caesar.

Beaufort cipher vs Vigenere

The Beaufort cipher belongs to the same family of keyword-based polyalphabetic ciphers as Vigenere. Both use a repeating keyword and a tabula recta style alphabet table.

The main difference is the encryption formula. In the Beaufort cipher, the key letter effectively determines the starting position and the plaintext letter is subtracted from it. This creates a reciprocal system where encryption and decryption use the same operation.

Although the practical security level is similar, Beaufort is often studied because of its elegant symmetry and historical use.

History of the Beaufort cipher

The Beaufort cipher is named after Sir Francis Beaufort, a British naval officer best known for creating the Beaufort wind force scale. The cipher became associated with military and naval communication during the nineteenth century.

Today it is mainly used in education, cryptography courses, and historical cipher collections. While no longer secure for real-world communication, it remains an important example of classical polyalphabetic encryption.

FAQ

Yes. The same transformation can be used for both encryption and decryption.

Only alphabet symbols participate in transformation; other characters are ignored in key stream.

No. Both use a repeating keyword, but the Beaufort cipher applies a different encryption rule and is reciprocal, meaning the same operation is used for encryption and decryption.

The Beaufort cipher is designed as a reciprocal cipher. Applying the algorithm again with the same keyword reverses the transformation automatically.

No. Like most classical ciphers, Beaufort can be broken with modern cryptanalysis and computing power. It is primarily used for learning and historical study.

Spaces, numbers, and punctuation marks are usually preserved unchanged. Only letters from the selected alphabet participate in encryption.

Sir Francis Beaufort was a British naval officer and hydrographer. The cipher bears his name and became associated with nineteenth-century military communication.
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