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# What is a Porta cipher?

Viewing 6 posts - 1 through 6 (of 6 total)
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• #87411
madness
Participant

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

#87426
ADecipher
Participant

Which challenge is the Porta Cipher?

#87450
madness
Participant

@ADecipher, NCC 2011 6B.

But that’s not what is the amazing thing.

#87463
f6exb
Participant

“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.

#87535
madness
Participant

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
```
#87709
madness
Participant

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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