Classical cipher

Porta Cipher

Encrypt or decrypt with a repeating keyword and the standard 26-letter ACA Porta tableau. Choose whether to retain the message layout or produce normalized cipher groups.

0 / 50,000 characters

Only ASCII letters A-Z are transformed. Other characters are preserved or removed according to the output format.

The effective key is the uppercase A-Z letters from this field. Limit: 128 entered characters.

The keyword advances on message letters only.

Action
Try an example:

No output yet.

How this version works

This tool uses the American Cryptogram Association 26-letter convention. Each keyword pair selects one reciprocal row: A/B selects the first row, C/D the second, and so on through Y/Z.

  1. The keyword is reduced to its ASCII letters and converted to uppercase.
  2. The key repeats across ASCII message letters. Spaces, digits, punctuation, and Unicode characters do not advance it.
  3. Every A-M letter swaps with one N-Z letter in the selected row. Applying the same transform again with the same key restores the normalized input.

Formatting choices

  • Preserve layout and case retains every non-ASCII-letter character and the case of transformed letters.
  • Letters only removes all other characters and returns uppercase text.
  • Groups of five uses the same letters-only result, separated into five-letter blocks.

ACA Porta tableau

Columns are A-M. Each row shows the paired N-Z letter. Pairing works in both directions.

KEY  A B C D E F G H I J K L M
A/B  N O P Q R S T U V W X Y Z
C/D  O P Q R S T U V W X Y Z N
E/F  P Q R S T U V W X Y Z N O
G/H  Q R S T U V W X Y Z N O P
I/J  R S T U V W X Y Z N O P Q
K/L  S T U V W X Y Z N O P Q R
M/N  T U V W X Y Z N O P Q R S
O/P  U V W X Y Z N O P Q R S T
Q/R  V W X Y Z N O P Q R S T U
S/T  W X Y Z N O P Q R S T U V
U/V  X Y Z N O P Q R S T U V W
W/X  Y Z N O P Q R S T U V W X
Y/Z  Z N O P Q R S T U V W X Y

Security note: Porta is a historical cipher for study and puzzles. It is not suitable for protecting confidential information.