Codes, Ciphers, Encryption and Cryptography

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Cryptography is the discipline of using codes and ciphers to encrypt a message and make it unreadable unless the recipient knows the secret to decrypt it. Encryption has been used for many thousands of years. The following codes and ciphers can be learned and used to encrypt and decrypt messages by hand.

Monoalphabetic Ciphers

A monoalphabetic cipher uses the same substitution across the entire message. For example, if you know that the letter A is enciphered as the letter K, this will hold true for the entire message. These types of messages can be cracked by using frequency analysis, educated guesses or trial and error.


Polyalphabetic Ciphers

In a polyalphabetic cipher, the substitution may change throughout the message. In other words, the letter A may be encoded as the letter K for part of the message, but later on it might be encoded as the letter W.


Polygraphic Ciphers

Instead of substituting one letter for another letter, a polygraphic cipher performs substitutions with two or more groups of letters. This has the advantage of masking the frequency distribution of letters, which makes frequency analysis attackes much more difficult.


Transposition Ciphers

Unlike substitution ciphers that replace letters with other letters, a transposition cipher keeps the letters the same, but rearranges their order according to a specific algorithm.

Other Ciphers and Codes

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