Hawkynt

Porta Cipher

Reciprocal polyalphabetic substitution cipher invented by Giovan Battista Bellaso in 1563. Uses 13-row substitution tableau where same operation encrypts and decrypts. Key feature is reciprocal property making it self-inverse.

Properties

Property	Value
Category	Classical Ciphers
Sub-category	Classical Cipher
Security status	🎓 Educational Only
Complexity	Intermediate
Inventor	Giovan Battista Bellaso
Year	1563
Origin	🇮🇹 Italy
Source	algorithms/classical/porta.js

Security

Status: 🎓 Educational Only

Known vulnerabilities

Issue	Description	Mitigation
Short keys create detectable repeating patterns vulnerable to Kasiski examination	—	Use longer, non-repeating keys
Only 13 effective substitution alphabets vs 26 in full polyalphabetic ciphers	—	Educational use only - not suitable for actual security

Documentation

• Wikipedia Article
• Historical Context
• Educational Tutorial

References

• dCode Implementation
• Practical Cryptography

Test vectors

3 vectors ship with this algorithm and run in the test suite. Byte values are hexadecimal.

Vector 1 — Practical Cryptography worked example - DEFENDTHEEASTWALLOFTHECASTLE under FORTIFICATION

Field	Value
key	464f5254494649434154494f4e
input	444546454e445448454541535457414c4c4f46544845434153544c45
expected	53594e4e4a534356524e524c41485554554b5543565259524c414e59

Vector 2 — Reciprocity - the same worked example run again on its own ciphertext returns the plaintext

Field	Value
key	464f5254494649434154494f4e
input	53594e4e4a534356524e524c41485554554b5543565259524c414e59
expected	444546454e445448454541535457414c4c4f46544845434153544c45

Vector 3 — First row of the published tableau read straight off - key letter A pairs A-M with N-Z

Field	Value
key	41
input	4142434445464748494a4b4c4d4e4f505152535455565758595a
expected	4e4f505152535455565758595a4142434445464748494a4b4c4d

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