Editing Transposition cipher (section)

== General principle ==
Plaintexts can be rearranged into a ciphertext using a [[Key (cryptography)|key]], scrambling the order of characters like the shuffled pieces of a [[jigsaw puzzle]]. The resulting message is hard to decipher without the key because there are many ways the characters can be arranged.

For example, the plaintext "THIS IS WIKIPEDIA" could be encrypted to "TWDIP SIHII IKASE". To decipher the encrypted message without the key, an attacker could try to guess possible words and phrases like DIATHESIS, DISSIPATE, WIDTH, etc., but it would take them some time to reconstruct the plaintext because there are many combinations of letters and words. By contrast, someone with the key could reconstruct the message easily:
 C I P H E R     Key
 1 4 5 3 2 6     Sequence (key letters in alphabetical order)
 T H I S I S     Plaintext
 W I K I P E
 D I A * * *
 
 Ciphertext by column:
   #1 TWD, #2 IP, #3 SI, #4 HII, #5 IKA, #6 SE
 Ciphertext in groups of 5 for readability:
   TWDIP SIHII IKASE
In practice, a message this short and with a predictable keyword would be broken almost immediately with [[Cryptanalysis|cryptanalysis techniques]].

Transposition ciphers have several vulnerabilities (see the section on "Detection and cryptanalysis" below), and small mistakes in the encipherment process can render the entire ciphertext meaningless.

However, given the right conditions - long messages (e.g., over 100–200 letters), unpredictable contents, unique keys per message, strong transposition methods, and so on - guessing the right words could be computationally impossible without further information. In their book on codebreaking historical ciphers, Elonka Dunin and Klaus Schmeh describe double columnar transposition (see below) as "one of the best manual ciphers known".<ref>{{Cite book |last1=Elonka |first1=Dunin |url=http://worldcat.org/oclc/1158165142 |title=Codebreaking: A Practical Guide |last2=Schmeh |first2=Klaus |publisher=Robinson |year=2020 |isbn=978-1-4721-4421-8 |pages=247 |oclc=1158165142}}</ref>