Double transposition cipher decoder and encoder

The double transposition cipher is considered one of the most secure ciphers that can be performed by hand. It is equivalent to using two columnar transposition ciphers, with same or different keys. During World War I and II, it was used by various agents and military forces.

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Double transposition cipher

Transposition grid


            

Options

Features

  • The double transposition cipher is an example of transposition cipher.
  • Until the VIC cipher, the double transposition cipher was considered as the most complicated cipher that an agent could operate reliably by hand.
  • It can encrypt any characters, including spaces and punctuation, but security is increased if spacing and punctuation is removed.
  • The message does not always fill up the whole transposition grid. The remaining of the transposition grid can then optionally be filled with a padding character, or left blank.
  • If the same key is used for encrypting multiple messages of the same length, they can be compared and attacked using a method called "multiple anagramming", finding solutions to both.

Sample text

uolbd reisi topic hpnoa rsnte

The ciphertext above represents "double transposition cipher" encrypted using the keys "secret" and "code".