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Cryptography uses encryption algorithms to make text unreadable, with the intended recipient using a key to decrypt it. Early ciphers used substitution or transposition, with modern algorithms being much more complex and secure.
Cryptography is the science of rendering text unreadable in order to pass it securely and secretly to the intended recipient, who uses a key to decrypt the message. An encryption algorithm is a defined series of steps to encrypt data. The original text is called the plaintext, and after the encryption algorithm has been applied to it, it is called the ciphertext. The encryption algorithm can be referred to as a cipher and is often given a name. For example, there is an encryption algorithm called Blowfish and another called AES (Advanced Encryption Standard), for example.
An encryption algorithm can depend on substitution, as in a substitution cipher, or on transposition, as in a transposition cipher. Examples of the earliest known ciphers were based on simple encryption algorithms. For example, Julius Caesar used a cipher that involved substitution in which he shifted the letters of the alphabet so that an A was represented by a D, a B was represented by an E, and so on. Since there are 26 letters in the alphabet, 25 such digits can be made: the 26th should replace A with A, which is not very secret. The key to this code can be thought of as the number of seats moved.
However, it is not necessary for an encryption algorithm to use letters. It can use numbers and other symbols as substitutes for letters. In the short story “The Gold Bug”, Edgar Allen Poe used a substitution cipher in which the encryption algorithm provides for this type of substitution, using symbols.
53##+305))6*;4826)4#.)4#);806*;48+8¶60))85;;)8*;:#*8+83(88)5*+;46(;88*96*?;8)*#(;485);5*+2:*#(;4956*2(5*-4)8¶8*;4069285);)6+8)4##;1(#9;48081;8:8#1;48+85;4)485+528806*81(#9;48;(88;4(#?34;48)4#;161;:188;#?;
If one were to solve this cipher, one would see that Poe did not assign the symbols to the letters in an orderly fashion with A = 1, B = 2, etc. So the encryption algorithm is a bit more complicated than the Alphabet Shift Algorithm. If you find one letter in one shift of the alphabet, you can easily derive them all. With Poe’s algorithm, on the other hand, knowing that A = 5, tells you nothing about B or any other letter.
The encryption algorithms used in modern applications, such as securing credit card transactions over the Internet, are much more complex. Keys can be up to 256 bits long or more. If they are to be hacked, it will only be with the help of computers. If the encryption key were to be obtained, however, the ciphertext could be read immediately.
