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Porta Cipher

Porta Cipher

Encrypt and decrypt Latin text with the Porta cipher online. Use a keyword, preserve spaces and punctuation, and work with the historical reciprocal polyalphabetic Porta table.

Input
0 chars · 0 bytes
Try:
Result
✓ Polyalphabetic substitution cipher ✓ We never store your messages ✓ Processed on our server
Examples
Encrypt HELLO WORLD
Key: PORTA
Input HELLO WORLD
Output OYTUB CHJUQ

Keyword: PORTA. The Porta table transforms each Latin letter while the space remains unchanged.

Encrypt a longer message
Key: SECRET
Input DEFEND THE EAST WALL
Output ZTTZLZ KWS ZPJK HOTN

Keyword: SECRET. The keyword repeats across the Latin letters of the message.

Decrypt with the same keyword
Key: PORTA
Input OYTUB CHJUQ
Output HELLO WORLD

Keyword: PORTA. Porta is reciprocal, so the same operation restores the original plaintext.

Preserve punctuation and numbers
Key: GUIDE
Input MEET AT 9 PM!
Output POVF PD 9 FQ!

Keyword: GUIDE. Digits, spaces, and punctuation stay unchanged; only Latin letters are encrypted.

How the Porta Cipher works

The Porta Cipher is a classical polyalphabetic substitution cipher that uses a keyword to choose one of thirteen paired alphabets for each letter of the message. The key letters are grouped into pairs: A/B, C/D, E/F, and so on through Y/Z. Letters from the same pair select the same Porta alphabet row.

As the text is processed, the keyword repeats across Latin letters only. Spaces, punctuation marks, numbers, and unsupported characters stay in place, so the layout of the message remains readable while the A-Z letters are transformed.

The most important feature of Porta is reciprocity. The same table and the same keyword are used for encryption and decryption, so applying the operation again restores the original text.

What this Porta Cipher tool does

This online Porta Cipher tool lets you encode and decode Latin text with a custom keyword. Enter plaintext to encrypt it, switch to decode mode for ciphertext, and use the same key in both directions because Porta is a reciprocal cipher.

The implementation follows the historical A-Z Porta table. It preserves uppercase and lowercase letters, ignores non-letter symbols in the keyword, and leaves non-Latin characters unchanged in the message.

Use it for cryptography lessons, puzzle making, CTF practice, checking historical examples, or comparing Porta with related keyword ciphers such as Vigenere and Beaufort. Like other classical ciphers, Porta is educational and not suitable for protecting sensitive information today.

FAQ

This implementation uses the historical Latin alphabet A-Z. Latin letters are encrypted or decrypted, while non-Latin characters are left unchanged.

Yes. Porta is reciprocal: applying the same Porta table with the same keyword converts plaintext to ciphertext and ciphertext back to plaintext.

Spaces, punctuation, numbers, and unsupported characters are preserved in the output. They also do not advance the keyword; only Latin letters consume key letters.

The keyword is repeated across the message. Each Latin key letter selects one of thirteen paired Porta alphabets: A and B select the same row, C and D select the same row, and so on.

Yes, but only Latin letters in the keyword are used. Spaces, digits, punctuation marks, and non-Latin symbols in the key are ignored.

Yes. Uppercase letters remain uppercase and lowercase letters remain lowercase in the result.

No. Porta is a historical classical cipher and can be attacked with modern cryptanalysis. Use it for education, puzzles, and demonstrations, not for real security.
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