44 Essential Cryptography Terms You Should Know [Glossary]

Do you want to learn encryption but have trouble communicating with the other experts? Jargon alone should not stop you from learning cryptography.

This is a list of 44 most essential cryptography terms to help you communicate with security experts and understand how cryptosystems work.

This glossary includes some of the most important words and vocabulary used in crypto space.

44 Cryptography Terms You Must Know!

Alphabet – The alphabet is the set of characters, which are affected by the encryption process. Normally, it is a set of 26 letters, but it can be made longer by adding punctuation marks and also numbers to enhance the security of a cipher.

Break – To break a code is to work out what the original message of an intercept text is.

Brute force attack – A brute force attack is a method of breaking a code by using all possible keys for a given cipher.

Cipher – A cipher is an algorithm, which changes the normal order and arrangement of letters within a message.

Cipher disc – A cipher disc is a tool used to help in encrypting and decrypting messages that use a Caesar Shift. It consists of two concentric discs, each split into 26 equal parts, and labelled with the letters of the alphabet. The inner disc is rotated in relation to the outer disc, so that differnet letters pair up.

Ciphertext – The ciphertext is the encrypted message that is sent to the recipient.

Ciphertext alphabet – A ciphertext alphabet is a way to quickly encrypt a message using a monoalphabetic substitution. It is represented as a table where the top row shows the plaintext letters, and the bottom row shows the ciphertext letter which is used to replace it.

Code – A code is a system where whole words and phrases are replaced by other words and phrases to hide their meaning.

Codebook – A codebook is an extensive book that contains all the words and phrases to be used in a code system. It shows the codeword for each normal word to encrypt the message, and the normal word for each codeword for when decrypting.

Crib – A crib is a portion of ciphertext, which is known to be an encryption of a specific phrase of plaintext.

Cryptanalysis – Cryptanalysis is the study of revealing the hidden meaning of an encrypted text, when one does not know the method used to encrypt it. It simply means code breaking.

Cryptography – Cryptography is the study of hiding the meaning of a message by changing the content of the message using rules. It involves ciphers and codes.

Cryptology – Cryptology is the study of hidden writings, or writings with hidden meanings. It involves cryptography and steganography.

Decrypt – To decrypt or decipher a message is to revert the ciphertext back into the plaintext using the cipher and key.

Digraph – A digraph is a pair of letters or characters.

Encrypt – To encrypt or encipher a message is to take the original message and perform specific changes to the text to create the ciphertext using a given cipher and key.

Fractionation – A fractionation method is one that represents single characters by a pair of characters.

Frequency analysis – Is a method used by cryptanalysts to break substitution ciphers. It is because in any given language, each letters has its own attributes, certain letters appear more frequently than others do. By analyzing, which letters appear frequently is an intercept; you can make identify the letters they could be representing.

Homophones – Using homophones is a way of disrupting the natural frequency of letters in a piece of text, and thus making frequency analysis difficult. It involves assigning multiple symbols to the higher frequency letters to even out the distribution.

Indicator block – An indicator block is a block of ciphertext used to hide a part of the key within the message itself. It is often used in the running key cipher to identify the page and line number to use within the key text as the start of the keystream.

Intercept – An intercept is a piece of encrypted text, which you do not know the cipher or the key used in the encryption process.

Interceptor – An interceptor is any person who comes across an encrypted message, and is not the intended recipient of the message. They have to break the code, since they do not know the cipher and key used.

Iterations – Iterations are how many times a particular cipher is applied. Some ciphers can be applied multiple times to make the encryption more secure. For example, transposition ciphers.

Kirchhoff’s principle – It states that a cryptosystem must remain secure if the algorithm of the cipher is known publicly, and the strength of the cipher should depend on the keeping the key secret.

Key – A key is a piece of information, which makes the encryption process unique and more secure.

Keyword – A keyword or keyphrase is a key, which takes the form of a word. It consists of a phrase instead of a word.

Keystream – A keystream is a string of letters that is as long as the plaintext. Each letters is used to identify which column of the tabula recta should be used in the encryption process of a polyalphabetic cipher.

Modulo – The basic principle is that items repeat after you reach the modulo number. In ciphers, this is usually the length of the alphabet. To take a number modulo another number is to take the remainder when you divide the first number by the second.

Monolaphabetic substitution cipher – A monoalphabetic substitution cipher is a cipher where each letter in the plaintext is replaced by the same letter or symbol every time.

Null – A null is a letter or symbol used as a placeholder in a message. It has no meaning. Often the letter “X” is used. It is used to make a message the right length for a particular cipher algorithm to be performed.

Numeric escape character – A numeric escape character is used in ciphers, which convert letters to numbers. The character “#” or “\” is used to indicate that the next number is actually a number, and not a piece of encrypted text.

Perfect secrecy – An idea in cryptography that all codes and ciphers aim for, perfect secrecy means that the cipher is truly unbreakable. The only known example of a cipher that has perfect secrecy is the one-time pad.

Plaintext – The plaintext is the original message before encryption.

Polyalphabetic substitution cipher – A polyalphabetic substitution cipher is one where the ciphertext alphabet changes according to some rule. It means that the same plaintext letter is not always encrypted to the same ciphertext letter. These ciphers were designed to overcome frequency analysis.

Polygraphic substitution cipher – A polygraphic substitution cipher replaces groups of letters or characters at a time. For example, the plaintext “ki” could be encrypted to “se”.

Recipient – The recipient of a message is the intended recipient when the message was sent. They know both the cipher and the key used, and thus they are able to decrypt the ciphertext.

Security – The security of cipher is a measure of how hard it is to break the code.

Sender – The sender of a message is the person who writes the original message and encrypts this for security reasons before sending the information to the recipient.

Shannon’s Maxim – This is a reformulation of the Kirchhoff’s principle, which states, “The attacker knows the system”. Assuming that the attacker will immediately gain a full working familiarity with any cryptographic system you use.

Steganography – Steganography is the study of physical means to hide a message, such as invisible inks and microdot.

Substitution cipher – A cipher where each letter (or groups of letters) of the plaintext is replaced by another letter or symbol in a predetermined way.

Tabula recta – A tabula recta is a table, which shows all the possible shifts of a given alphabet in one place. You choose the letters from the keystream across the top, and the plaintext letters down the left hand side, and the ciphertext letter is the column and row that represents these two pieces of information.

Transparency – A transparency is when a character (or group of characters) encrypt to themselves. A cipher system that produces many transparencies is less secure.

Transposition cipher – A cipher where the order of the letters in the message is changed. The same letters appear, but they are mixed up in a non-sensible manner.


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