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Porta Cipher

Tool to decrypt / encrypt with Porta cipher. Invented by an Italian physicist Della Porta, this poly alphabetical cipher changes of alphabet every letter.

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Porta Cipher -

Tag(s) : Cryptography, Poly-Alphabetic Cipher

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Porta Cipher

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Tool to decrypt / encrypt with Porta cipher. Invented by an Italian physicist Della Porta, this poly alphabetical cipher changes of alphabet every letter.

Answers to Questions

How to encrypt using Porta cipher?

The encryption by Porta uses a key and a series of 13 reversible alphabets each associated with 2 letters of the alphabet: A and B for the first, C and D for the second, and so on.

Example: The alphabets used by default are:

ABABCDEFGHIJKLM
NOPQRSTUVWXYZ
NOPQRSTUVWXYZABCDEFGHIJKLM
CDABCDEFGHIJKLM
ZNOPQRSTUVWXY
ZNOPQRSTUVWXYBCDEFGHIJKLMA
EFABCDEFGHIJKLM
YZNOPQRSTUVWX
YZNOPQRSTUVWXCDEFGHIJKLMAB
GHABCDEFGHIJKLM
XYZNOPQRSTUVW
XYZNOPQRSTUVWDEFGHIJKLMABC
IJABCDEFGHIJKLM
WXYZNOPQRSTUV
WXYZNOPQRSTUVEFGHIJKLMABCD
KLABCDEFGHIJKLM
VWXYZNOPQRSTU
VWXYZNOPQRSTUFGHIJKLMABCDE
MNABCDEFGHIJKLM
UVWXYZNOPQRST
UVWXYZNOPQRSTGHIJKLMABCDEF
OPABCDEFGHIJKLM
TUVWXYZNOPQRS
TUVWXYZNOPQRSHIJKLMABCDEFG
QRABCDEFGHIJKLM
STUVWXYZNOPQR
STUVWXYZNOPQRIJKLMABCDEFGH
STABCDEFGHIJKLM
RSTUVWXYZNOPQ
RSTUVWXYZNOPQJKLMABCDEFGHI
UVABCDEFGHIJKLM
QRSTUVWXYZNOP
QRSTUVWXYZNOPKLMABCDEFGHIJ
WXABCDEFGHIJKLM
PQRSTUVWXYZNO
PQRSTUVWXYZNOLMABCDEFGHIJK
YZABCDEFGHIJKLM
OPQRSTUVWXYZN
OPQRSTUVWXYZNMABCDEFGHIJKL

The Porta algorithm consists of taking the first letter of the key, finding the corresponding alphabet, and making a substitution of the first letter of the plain text with this alphabet.

Example: Encrypt the message DCODE with the key PORTA. The first letter of the key P corresponds to the alphabet TUVWXYZNOPQRSHIJKLMABCDEFG, which allows to substitute the letter D with P

The encryption is continued by taking the second letter of the key and the corresponding alphabet and substituting the second letter of the plain text, with this second alphabet and so on.

Example: DCODE is then encrypted WVJUR.

How to decrypt Porta cipher?

Decryption is the same as encryption if alphabets are reversible.

What are common Porta alphabets?

Several sets of reversible alphabets are mentioned, including:

NOPQRSTUVWXYZABCDEFGHIJKLM
ZNOPQRSTUVWXYBCDEFGHIJKLMA
YZNOPQRSTUVWXCDEFGHIJKLMAB
XYZNOPQRSTUVWDEFGHIJKLMABC
WXYZNOPQRSTUVEFGHIJKLMABCD
VWXYZNOPQRSTUFGHIJKLMABCDE
UVWXYZNOPQRSTGHIJKLMABCDEF
TUVWXYZNOPQRSHIJKLMABCDEFG
STUVWXYZNOPQRIJKLMABCDEFGH
RSTUVWXYZNOPQJKLMABCDEFGHI
QRSTUVWXYZNOPKLMABCDEFGHIJ
PQRSTUVWXYZNOLMABCDEFGHIJK
OPQRSTUVWXYZNMABCDEFGHIJKL
or
NOPQRSTUVWXYZABCDEFGHIJKLM
OPQRSTUVWXYZNMABCDEFGHIJKL
PQRSTUVWXYZNOLMABCDEFGHIJK
QRSTUVWXYZNOPKLMABCDEFGHIJ
RSTUVWXYZNOPQJKLMABCDEFGHI
STUVWXYZNOPQRIJKLMABCDEFGH
TUVWXYZNOPQRSHIJKLMABCDEFG
UVWXYZNOPQRSTGHIJKLMABCDEF
VWXYZNOPQRSTUFGHIJKLMABCDE
WXYZNOPQRSTUVEFGHIJKLMABCD
XYZNOPQRSTUVWDEFGHIJKLMABC
YZNOPQRSTUVWXCDEFGHIJKLMAB
ZNOPQRSTUVWXYBCDEFGHIJKLMA

How to recognize a Porta ciphertext?

The message has a low index of coincidencehref due to the use of several alphabets.

How to decipher Porta without key?

A Friedman test retrieves the key length probabilistically.

What are the variants of the Porta cipher?

This is not a variant but Porta is similar to the Bellasohref Cipher, another Italian, who uses several alphabets.

When Porta have been invented ?

In the 16th centuryhref

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Source code

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Questions / Comments


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