What is cryptography?

(upbeat music) - So, what is cryptography and cryptology? Cryptology is the overall study of codes and ciphers. Cryptography is the science and field of using codes and ciphers to create encryption mechanisms and secure communications. Securing information means protecting data when it's in transit or in motion and when it is stored, say on disc. The word cryptography comes from two Greek words meaning hidden writing. Cryptography has been at the foundation of communication, including computing communication, for well over 50 years. It focuses on the mechanisms of encrypting data. Depending on the cryptographic method involved, various properties fall out of its use. Confidentiality ensures that only the intended recipient can decrypt a message or data and read its contents. Nonrepudiation means that the sender of a message cannot deny sending or creating the message. Integrity focuses on ensuring that information hasn't been altered or deleted without authorization. Authenticity verifies that what you have is sent from a legitimate actual user. Cryptography is a science that continues to advance. Various advances in cryptography have made it harder and harder to break encryptions. Authentication and authorization strategies are not enough to protect against unwanted access to data. (upbeat music) So, when talking about cryptography we often use the terms code and cipher. Well, how are they different and how are they used together? Codes are substitution. These are where a symbol is replaced by another symbol, letters for numbers. Think about hieroglyphics or translation into another alphabet. Sometimes code replaces words with other words or phrases. For example, the phrase "The eagle has landed" was famously used by Neil Armstrong when Apollo 11 landed on the moon, but it also has a history of use in military operations. Sending telegraphs is another form of code where individual letters and numbers are changed into sequences of dots and dashes in a predictable way. Another historical example is that of the Navajo code talkers during World War II where information that was transmitted over the radio was translated into the Navajo language by the code talkers where they replaced words with other words in Navajo, such as turtle for tank. To use a code, one has to understand the translation from symbol to symbol or words to words. This may involve a code book. You look up the item in the code book, find its corresponding value, and send that. Decoding works in the inverse manner. So, when thinking about hieroglyphics as a form of coding, the Rosetta Stone is a form of code book used to decipher what the hieroglyphs meant. A cipher is different than a code. A cipher involves a transformation of the underlying letters, numbers, or binary bits on a computer. It involves shuffling them around in such a way that it obscures completely the meaning. It's either a mathematical computation that's done in a computer or a mechanical translation that may be done by a machine. What's put out from this is cipher text. It is an unreadable, encrypted form of the plain text that went into the system. One example of a cipher is a rotation cipher. This is where the letters of the alphabet are shifted up or down in the alphabet for each letter by a fixed or variable amount. One very common version of this is called ROT13, or Rotation 13, that has been used on the internet for some time as a way to somewhat obfuscate texts that shouldn't be seen immediately. (upbeat music) Codes and ciphers may be used together. In the 1950s, Soviet spies would take Russian messages, translate them using a code book into groups of numbers, and then use a cipher to encrypt those numbers to send their message. On the other side, an encryption algorithm would translate the encrypted message back into the groups of numbers. Those would then be looked up in the code book to result in the message that's being sent. A cipher or a code use a key. The key may be an algorithm and it may be a value used to initialize the algorithm to scramble the message. The strength of the encryption is based on the difficulty of someone reversing the process to be able to read a message. The best algorithms depend on the secrecy of the key rather than on hiding the algorithm. (upbeat music)