What is a Porta cipher?

[madness]

The Porta cipher is a Quagmire 4, and I can prove it.

[ADecipher]

Which challenge is the Porta Cipher?

[madness]

@ADecipher, NCC 2011 6B.

But that’s not what is the amazing thing.

[f6exb]

“The Porta cipher is a Quagmire 4, and I can prove it.”

I have seen the paper, but I haven’t read it yet and I think I won’t understand anything.

[madness]

OK, well, if you make a Q4 with these alphabet keys
AYCWEUGSIQKOMZBXDVFTHRJPLN NLPJRHTFVDXBZMOKQISGUEWCYA
and translate the shift key according to this table,
then encryption and decryption are the same as the Porta.

Porta, American      Porta, British       Q4
A,B                  A,B                  N
C,D                  Y,Z                  O
E,F                  W,X                  P
G,H                  U,V                  Q
I,J                  S,T                  R
K,L                  Q,R                  S
M,N                  O,P                  T
O,P                  M,N                  U
Q,R                  K,L                  V
S,T                  I,J                  W
U,V                  G,H                  X
W,X                  E,F                  Y
Y,Z                  C,D                  Z

[madness]

Here’s how to fake a Porta cipher with a Beaufort cipher:

Take your plaintext P.
Encrypt P with a monoalphabetic substitution cipher with key AOCQESGUIWKYMZLXJVHTFRDPBN.
Encrypt the result with a Beaufort, after changing the key according to the table below.
Encrypt the result with a monoalphabetic substitution cipher with key AYCWEUGSIQKOMZBXDVFTHRJPLN.
The result is your ciphertext C, which can be decrypted as a Porta.

Porta, American      Porta, British       Beaufort
A,B                  A,B                  Z
C,D                  Y,Z                  L
E,F                  W,X                  X
G,H                  U,V                  J
I,J                  S,T                  V
K,L                  Q,R                  H
M,N                  O,P                  T
O,P                  M,N                  F
Q,R                  K,L                  R
S,T                  I,J                  D
U,V                  G,H                  P
W,X                  E,F                  B
Y,Z                  C,D                  N

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