What is a Cryptographic Key?
In cryptography, a key is a string of characters used in a cryptographic algorithm to alter(lock) the data in such a way that it can be decrypted(unlocked) only by someone with the right key.
encrypt(“Hello world!”, key) = “U2FsdGVkX18zIUJRbr2nYpavPTPcDp4WxVV5X4qmwf4=”
The original data is named in cryptographic terms “plain text”, while the encrypted(locked) plain text is called cyphertext.
Before the era of computers, the ciphertext was quite simple compared to its modern counterparts, mainly they were based on substitution and shifting the plaintext by a certain number of characters. Few famous examples of ciphertext include:
- The Caesar Shift Cipher
Its first appearance is dated around the first Century AD in the Roman Empire, the chipper was named in honor of Julius Caesar which according to the historian Suetonius used it to encrypt secret messages. Due to the low level of literacy among the citizens of the roman empire the cipher remained secure during the roman era, after the demise of the roman empire, around 9th century AD, historical records exist which document multiple ways to crack it using frequency analysis from Al-Kindi.
Was a simple form of cryptography used in antiquity in Greece, Scytale is a simple tool of cylindrical form with a strip of parchment wound around it on which a message is written, used to form a transposition cipher, it was mainly used to communicate during military campaigns. The Recipient of the message would use a rod of exact same length on which it would wrap the message in order to decrypt it.
It is a method of hiding messages in plain text disguised as something else, the earliest record which documents the usage of this method was described by Herodotus in the Histories. Herodotus describes how the leader of the Ionian city of Miletus, in the late century BC, sent a message to one of his vassals by shaving the head of his most trusted servant and marking the message on onto his scalp, and then letting the slaves har regrow, on arrival to the destination the servant was ordered to shave again such that the recipient can “decrypt” the message.