Key Cryptography Basics

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Key Cryptography Basics Problems with internet transactions As discussed in class there are several problems with internet communication. The major three are: Eavesdropping is the risk of having private information viewed as it travels from sender to recipient by a third party. The most popular fear is having your credit card number and information stolen while purchasing something online, but this would apply to any private information delivered over the internet. Tampering is the risk of a third party intercepting a private transaction of information and changing it. An example of this would be altering the recipient fields on a purchase order. Impersonation is the risk of someone impersonating a trusted recipient in order to receive private information. This Encryption Cryptograms in the newspaper are probably one of the most basic forms of encryption. A simple system of swapping letters for other letters is used to disguise the message making it indistinguishable to anyone who does not know the rules of the system. Even though the cryptogram system is so simplistic it is actually considered sporting to crack, the basic logic of encoding is the same for more sophisticated methods. Key Based Encryption (symmetric encryption) In this example of Key based encryption we first create a number conversion table so that we can apply mathematical rules to our message after converting it. Number Conversion Table: a b C d e f g h i j k l m 1 2 3 4 5 6 7 8 9 10 11 12 13 n o P q r s T u v w x y z Space 14 15 16 17 18 19 20 21 22 23 24 25 26 0 Then we decide upon a key. In order to decipher this code the recipient will also be required to posses this key. It will become obvious by the end of our example that the shorter the key the easier the code will be to crack. Key: Encrypted We then take the message and the key convert them using the conversion table and add them together. Then in order to reassign them to a letter value we take the mod base 27 in order to restrict the letter assignment to numbers within the 0 to 27 table. Message: on the internet nobody knows you are a dog

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