2/18/2023 0 Comments Veni vidi vici symbol![]() What is the general process for encrypting a single character? Let's use a variable, c, to represent the plaintext letter that we are encrypting. We can use these functions to come up with the ciphertext given the key and the direction. For example, if we call letter_from_number with the argument 1, the value of the expression is b. For example, if we call number_from_letter with the argument d, the return value is 3.Īssume that we have another function named letter_from_number that turns a number between 0 and 25, inclusive, into a letter from the alphabet: 0 is a, 1 is b, 2 is c, etc. Assume that we have a function named number_from_letter that turns a letter into its position in the alphabet: a is 0, b is 1, c is 2, etc. Implementing the Caesar Cipher is done with modulo arithmetic and by equating each letter with a number according to its position in the alphabet. To be able to read the secured message, my parents would shift each letter of the ciphertext to the left by 5 and recover the original plaintext. Why? Because m is five letters to the right of h in the alphabet, j is five letters to the right of e in the alphabet, and so on. I would encrypt the message "hello" as "mjqqt". We would agree that I would encrypt my messages by shifting each letter 5 (the shift number) characters to the right (the direction). It is called a substitution cipher because each letter in the plaintext is substituted for a letter in the ciphertext.Īssume that I want to communicate with my parents. A type of substitution cipher, the sender and receiver agree on the key - a shift number and direction (left or right) - and, to encrypt, the sender shifts each letter in the plaintext in the chosen direction and by the number of spaces indicated by the shift number to create the ciphertext and, to decrypt, the receiver shifts each letter in the ciphertext in the opposite direction and same amount to restore the plaintext. One of the earliest encryption schemes was employed by Julius Caesar to keep his messages safe. Using a good encryption/decryption scheme and key to protect a message means that the sunglassed snooper has no way of knowing the contents of the message even if they know the algorithm used to protect the message. The data shared between communicating parties that can be used to configure the encryption/decryption scheme is called a key. If the methods of encryption and decryption are known, why can't the sender's foes use that information to recover the plaintext? Because encryption/decryption schemes usually rely on the sender and the intended recipient sharing some data that is used to configure the encryption/decryption scheme in a particular way. In an encryption/decryption scheme, there is a corresponding algorithm for taking the ciphertext and reversing the encryption - the process is known as decryption and is performed by the receiver.Įncryption/decryption schemes are publicly known, well documented and standardized. This process is known as encryption and is performed by the sender. In an encryption/decryption scheme, there is an algorithm for taking the original message (the plaintext) and transforming it to something that an eavesdropper can't understand (the ciphertext). The need led to the development of encryption.Įncryption/decryption methods are known as schemes. ![]() In other words, the sender and receiver had to assume that the spy knew the method by which they were keeping a secret and still be able to communicate privately. What the secretive sender needed to communicate with the reluctant reader was a method of communicating that could protect the information whether a spy knew the means for its protection or not. ![]() The technique of " security through obscurity" did not hold up long when exposed to dedicated adversaries. Whether by hiding the truth or using trusted intermediaries, early furtive senders would rely on surreptitiousness to keep a message secret. The battle between the coy and the nosy has been fought back and forth throughout the ages. No matter the mechanism, there have always been people who wanted to keep certain communications secret.Īnd, for as long as there have been secrets, there have been people dedicated to exposing them. Sometimes the writer would mail a letter and seal it with a wax stamp to indicate to the reader whether the message had been opened in transit. Sometimes the speaker would tell the message to a trusted courier who would deliver the message to the speaker's counterpart. Since the beginning of time people have sent messages that they only wanted the intended recipient to understand.
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