Ciphertext is encrypted text that contains a form of the original plaintext that is unreadable by both computers and humans without the algorithm and the key that was used to encrypt it.
To put it simply, ciphertext is data that has been encrypted and it’s unreadable until it has been converted into plaintext with a key. It is also called cyphertext.
Read: Introduction to Cryptography.
Here are some terminology related to ciphertext:
- Plaintext, this is simply information readable by both humans and computers. It can be in many forms like hard copy text, music, movies and computer programs.
- Encryption, is simply the process of converting plaintext to ciphertext.
- Decryption, is the reverse process of encryption. Reverting cipertext to plaintext.
- Cipher, this is the algorithm used to turn plaintext into ciphertext and also reverting ciphertext to plaintext.
In this guide I will be discussing the following:
- How to convert plaintext to ciphertext.
- Difference between a cipher and ciphertext.
- Difference between ciphertext and plaintext.
- Ciphertext attack types.
- List of famous ciphertexts.
1) How to convert plaintext to ciphertext
There are many types of ciphers in cryptography including:
- Substitution ciphers.
- Transposition ciphers
- Polyalphabetic ciphers.
- Permutation ciphers.
- Monoalphabetic ciphers.
In this article I will use a simple substitution cipher called Caesar cipher. It simple shifts every letter of the alphabet by given number of spaces defined by the key.
Here is an example:
Plaintext: Learning ciphers and codes is fun.
First I need to generate the ciphertext alphabet using a specific key. In this case the key is 3.
Then to encode the plaintext, I simply convert every letter of my message with its equivalent in the ciphertext alphabet.
Thus, the ciphertext is: ohduqlqj flskhuv dqg frghv lv ixq.
2) What is the difference between a cipher and ciphertext
Ciphertext is the output of an encryption process, and the input of a decryption process while plaintext is information in human readable form.
- Read: What is a cipher.
A cipher is an encryption algorithm while ciphertext is an output of a given cipher.
3) What is the difference between ciphertext and plaintext
Cipher text is written in encrypted form and people can’t understand or decode it while plain text is just normal text written in any human understandable language like English.
Plaintext is an input for an encryption algorithm and can be in form of text, audio, video and also images.
4) Ciphertext attack types
The technique used to break ciphertext in order to understand the message encoded is called cryptanalysis.
There are many cryptanalysis techniques for breaking any ciphertext though some are more efficient than others.
Here are some types of ciphertext attacks models to crack a cipher:
- Ciphertext-only, possible when you have a collection of ciphertexts.
- Known-plaintext, this is done when one have a set of ciphertexts to which they know the corresponding plaintext.
- Chosen-plaintext attack, involves obtaining ciphertext corresponding to an arbitrary set of plaintexts of your own.
- Batch chosen-plaintext attack, choosing all plaintexts before any of them are encrypted.
- Adaptive chosen-plaintext attack, choosing subsequent plaintexts based on the information from previous encryptions.
- Chosen-ciphertext attack, involves taking the plaintexts corresponding to an arbitrary set of ciphertexts of your own.
- Related-key attack, where the keys are unknown but you have ciphertexts that are encrypted using two different keys.
5) List of ciphertexts
Here is a list of the most famous ciphertexts:
- Beale ciphers.
- The Bletchley Park cipher.
- The Book of the Law.
- Copiale cipher.
- D’Agapeyeff cipher.
- Dorabella cipher.
- The Magic words are Squeamish Ossifrage.
- Markovian Parallax Denigrate.
- The cryptogram in “The Gold-Bug”.
- The Babington plot ciphers.
- Tamam Shud case.
- Smithy code, embedded within the 2006 judgement on the Da Vinci code case.
- Voynich manuscript.
- The Zimmermann telegram.
- Zodiac killer ciphers.
- Cryptogram of Olivier Levasseur.
- Ricky McCormick’s encrypted notes.
- The use of the purple (cipher machine) by Japan before the Pearl Harbor attack.
- The Rohonc codex.
- The Shugborough inscription.
Now I want to hear from you.
What are some of your favorite ciphertexts?
Or maybe I missed an important aspect of ciphertext.
Either way, let me know by leaving a comment below.