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Encryption

Explain the term Encryption.

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Encryption: At the core of most security services are encryption algorithms. These are functions that take as input a stream of bits (plaintext) and produce an output (cipher text) that bears no resemblance to the input. The encryption algorithm is reversible hence an authorized party can take the output and recover the original input. This process is called decryption. Encryption/decryption algorithms by themselves are very difficult to keep secret, and if revealed would invalidate the algorithm for future use. Hence, modern algorithms also include a key which will determine exactly how the algorithm will work in a given situation. If the key is compromised a new key can be chosen and the same algorithm can be used.

The primary characteristic of an encryption algorithm (and the usual approach to attacking one) is that there are no repetitive patterns in the cipher text and that patterns in the cipher text can not be related to simi lar patterns in the plaintext. For example, consider the simple substitution codes, which offset the alphabet by a fixed number of characters. So that A maps to F, B maps to G, and so on wrapping around when it gets to the end so that Z maps to E. It turns out that the frequencies of certain letters in different languages are well known and can be used to break a code like this quite easily. Similar patterns can be found for pairs of characters, etc. So a good encryption algorithm must try to mask the patterns that are inherent in the plaintext.

Encryption algorithms are classified into two broad categories-symmetric and asymmetric. These two categories differ in the number of different keys used, the operations performed, and the algorithm efficiency.

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