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Ciphers Transcription

Welcome to our ciphers module. There are several different types of ciphers that we use in cryptography. A cipher is some type of system of converting plain text or unencrypted data to cipher text or encrypted data by rearranging characters, bits, or blocks of bits contained in the message. With a transposition cipher, we simply rearrange characters in a plain text message.

As you can see here, we have the word cipher, which then becomes R-H-I-E-P-C. We aren't really disguising any of the letters, we're just moving them around. With a substitution cipher we take a certain character in the plain text and replace it with a different character. The Caesar cipher is one of the earliest known examples of this type of cipher.

Here we shift all of the letters three places to the right in the alphabet. So c becomes f, i becomes l, p becomes s, and so on. With a mono-alphabetic cipher, we only use one alphabet. Which makes it very easy to use frequency analysis because of the popularity of certain words in the English language.

With poly-alphabetic ciphers, we use multiple alphabets so we can replace the same character with different characters during each round of encryption. Which makes it much harder for an attacker to determine what our plan text message was before it was encrypted. We have two different types of ciphers, block ciphers and stream ciphers.

A block cipher takes a chunk of the data to be encrypted and encrypts that entire block at one time. This is used in most modern algorithms and an example here is a transposition cipher. With a stream cipher, we only encrypt one bit, or one character, at a time, and this is known as the data stream.

The examples here are the Caesar cipher, and One Time Pads. For the CISSP exam, you should be familiar with the difference between a stream cipher and a block cipher. And very simply a stream cipher encrypts the data one bit at a time as it streams into the algorithm.

And a block cipher breaks up the data to be encrypted into blocks and then encrypts the data one block at a time. This concludes our ciphers module. Thank you for watching.