In cryptography, a cipher (or cypher) is an algorithm for performing encryption or decryption—a series of well-defined steps that can be followed as a procedure. An alternative, less common term is encipherment. To encipher or encode is to convert information into cipher or code. In common parlance, "cipher" is synonymous with "code", as they are both a set of steps that encrypt a message; however, the concepts are distinct in cryptography, especially classical cryptography. Codes generally substitute different length strings of characters in the output, while ciphers generally substitute the same number of characters as are input. There are exceptions and some cipher systems may use slightly more, or fewer, characters when output versus the number that were input. Codes operated by substituting according to a large codebook which linked a random string of characters or numbers to a word or phrase. For example, "UQJHSE" could be the code for "Proceed to the following coordinates." When using a cipher the original information is known as plaintext, and the encrypted form as ciphertext. The ciphertext message contains all the information of the plaintext message, but is not in a format readable by a human or computer without the proper mechanism to decrypt it. The operation of a cipher usually depends on a piece of auxiliary information, called a key (or, in traditional NSA parlance, a cryptovariable). The encrypting procedure is varied depending on the key, which changes the detailed operation of the algorithm. A key must be selected before using a cipher to encrypt a message. Without knowledge of the key, it should be extremely difficult, if not impossible, to decrypt the resulting ciphertext into readable plaintext. Most modern ciphers can be categorized in several ways * By whether they work on blocks of symbols usually of a fixed size (block ciphers), or on a continuous stream of symbols (stream ciphers). * By whether the same key is used for both encryption and decryption (symmetric key algorithms), or if a different key is used for each (asymmetric key algorithms). If the algorithm is symmetric, the key must be known to the recipient and sender and to no one else. If the algorithm is an asymmetric one, the enciphering key is different from, but closely related to, the deciphering key. If one key cannot be deduced from the other, the asymmetric key algorithm has the public/private key property and one of the keys may be made public without loss of confidentiality. (Wikipedia).
An informal introduction to cryptography. Part of a larger series teaching programming at http://codeschool.org
From playlist Cryptography
Symmetric Key Cryptography: The Keyword Cipher
This is the second in a series about cryptography; an extremely important aspect of computer science and cyber security. It covers a substitution cipher called the keyword cipher, also known as the Vigenère cipher. It explains how a keyword, or key phrase, can be used to effectively gene
From playlist Cryptography
Symmetric Key Cryptography: The Caesar Cipher
This is the first in a series about cryptography; an extremely important aspect of computer science and cyber security. It introduces symmetric key cryptography with a well known substitution cipher, namely the Caesar Cipher. It includes a few examples you can try for yourself using diff
From playlist Cryptography
Cryptograph: Substitution Cipher (Caesar Cipher)
This lesson explains how to encrypt and decrypt a message using a Caeser cipher. Site: http://mathispower4u.com
From playlist Cryptography
An informal introduction to cryptography. Part of a larger series teaching programming at http://codeschool.org
From playlist Cryptography
From playlist Week 2 2015 Shorts
Perfect Cipher - Applied Cryptography
This video is part of an online course, Applied Cryptography. Check out the course here: https://www.udacity.com/course/cs387.
From playlist Applied Cryptography
Modern Symmetric Ciphers - Applied Cryptography
This video is part of an online course, Applied Cryptography. Check out the course here: https://www.udacity.com/course/cs387.
From playlist Applied Cryptography
Follow-up: Barbie electronic typewriter
Here is a copy of the description from the Barbie video: ---- I first found this story on the crypto museum website, which has great information about the Barbie typewriter (and other cipher machines) https://www.cryptomuseum.com/crypto/mehano/barbie/ ------- Thanks to Sarah Everett fr
From playlist My Maths Videos
Cryptography and Network Security by Prof. D. Mukhopadhyay, Department of Computer Science and Engineering, IIT Kharagpur. For more details on NPTEL visit http://nptel.iitm.ac.in
From playlist Computer - Cryptography and Network Security
Live CEOing Ep 544: Language Design in Wolfram Language [Ciphers & WFR Submissions] [Part 01]
In this episode of Live CEOing, Stephen Wolfram discusses upcoming improvements and features to the Wolfram Language. If you'd like to contribute to the discussion in future episodes, you can participate through this YouTube channel or through the official Twitch channel of Stephen Wolfram
From playlist Behind the Scenes in Real-Life Software Design
Cryptography and Network Security by Prof. D. Mukhopadhyay, Department of Computer Science and Engineering, IIT Kharagpur. For more details on NPTEL visit http://nptel.iitm.ac.in
From playlist Computer - Cryptography and Network Security
What is Bill Cipher? (Scientific Analysis)
What is Bill Cipher? Today we discover the very very confusing science of what Gravity Fall's Bill Cipher is. =======WARNING VERY VERY CONFUSING======= This video talks about dimensions and alternate universes. Your mind might explode! Sources: -http://en.wikipedia.org/wiki/Four-dim...
From playlist Scientific Videos
Cryptography and Network Security by Prof. D. Mukhopadhyay, Department of Computer Science and Engineering, IIT Kharagpur. For more details on NPTEL visit http://nptel.iitm.ac.in
From playlist Computer - Cryptography and Network Security
The Barbie electronic typewriter - with Just My Typewriter
I first found this story on the crypto museum website, which has great information about the Barbie typewriter (and other cipher machines) https://www.cryptomuseum.com/crypto/mehano/barbie/ ------- Thanks to Sarah Everett from Just My Typewriter, check out her channel here: https://www.y
From playlist My Maths Videos
25c3: An introduction to new stream cipher designs
Speaker: Tor E. Bjørstad Turning data into line noise and back Even with "nothing to hide", we want to protect the privacy of our bits and bytes. Encryption is an important tool for this, and stream ciphers are a major class of symmetric-key encryption schemes. Algorithms such as RC4 (us
From playlist 25C3: Nothing to hide
Cryptography and Network Security by Prof. D. Mukhopadhyay, Department of Computer Science and Engineering, IIT Kharagpur. For more details on NPTEL visit http://nptel.iitm.ac.in
From playlist Computer - Cryptography and Network Security
One Time Pad - Applied Cryptography
This video is part of an online course, Applied Cryptography. Check out the course here: https://www.udacity.com/course/cs387.
From playlist Applied Cryptography