digplanet beta 1: Athena
Share digplanet:

Agriculture

Applied sciences

Arts

Belief

Chronology

Culture

Education

Environment

Geography

Health

History

Humanities

Language

Law

Life

Mathematics

Nature

People

Politics

Science

Society

Technology

In classical cryptography, a permutation cipher is a transposition cipher in which the key is a permutation.

To apply a cipher, a random permutation of size e is generated (the larger the value of e the more secure the cipher). The plaintext is then broken into segments of size e and the letters within that segment are permuted according to this key.

In theory, any transposition cipher can be viewed as a permutation cipher where e is equal to the length of the plaintext; this is too cumbersome a generalisation to use in actual practice, however.

## Identifying the cipher

Because the cipher doesn't change any of the characters, the ciphertext will have exactly the same letter frequencies as the underlying plaintext. This means that the cipher can in many cases be identified as a transposition by the close similarity of its letter statistics with the letter frequencies of the underlying language.

## Breaking the cipher

Because the cipher operates on blocks of size e, the plaintext and the ciphertext have to have a length which is some multiple of e. This causes two weaknesses in the system: first, the plaintext may have to be padded (if the padding is identifiable then part of the key is revealed) and second, information relating to the length of the key is revealed by the length of the ciphertext. To see this, note that if the ciphertext is of length i then e must be one of the divisors of i. With the different possible key sizes different possible permutations are tried to find the permutation which results in the highest number of frequent bigrams and trigrams as found in the underlying language of the plaintext. Trying to find this permutation is essentially the same problem encountered when analysing a columnar transposition cipher: multiple anagramming.

Original courtesy of Wikipedia: http://en.wikipedia.org/wiki/Permutation_cipher — Please support Wikipedia.
A portion of the proceeds from advertising on Digplanet goes to supporting Wikipedia.
 67 videos foundNext >
 transposition netwinznetwinz TRANSPOSITION CIPHER Introduction: In cryptography, a transposition cipher is method of encryption by which the positions held by units of plaintext ... (4/6) World War II Code BreakersWorld War II Videos The Purple Machine was an Allied codename for one of several Japanese cipher machines used during World War Two. The nickname Purple Mach... (1/6) World War II Code BreakersThe Purple Machine was an Allied codename for one of several Japanese cipher machines used during World War Two. The nickname Purple Machine was derived from... (2/6) World War II Code BreakersWorld War II Videos The Purple Machine was an Allied codename for one of several Japanese cipher machines used during World War Two. The nickname Purple Mach... C++: Creating a Cipher SolverIt's been a considerable amount of time since I last uploaded a C++ video. This is partly due to the fact I had a bit of a hiatus due to exams and then never... (3/6) World War II Code BreakersWorld War II Videos The Purple Machine was an Allied codename for one of several Japanese cipher machines used during World War Two. The nickname Purple Mach... (5/6) World War II Code BreakersWorld War II Videos The Purple Machine was an Allied codename for one of several Japanese cipher machines used during World War Two. The nickname Purple Mach... (6/6) World War II Code BreakersWorld War II Videos The Purple Machine was an Allied codename for one of several Japanese cipher machines used during World War Two. The nickname Purple Mach... 11- Encrypt Decrpt with Reverse - Rail Fence-2.mp4 Dynamic Credentials and Ciphertext Delegation for Attrib ...Talk at crypto 2012. Authors: Amit Sahai, Hakan Seyalioglu, Brent Waters. See http://www.iacr.org/cryptodb/data/paper.php?pubkey=24290.
 67 videos foundNext >

We're sorry, but there's no news about "Permutation cipher" right now.

 Limit to books that you can completely read online Include partial books (book previews) .gsc-branding { display:block; }

Oops, we seem to be having trouble contacting Twitter