CryptologyCryptologyCryptologyCryptologyTim CahillTim Cahill

Ryan ChurchRyan Church

Cryptology• Cryptology - the science and study of cryptanalysis and

cryptography.

• Cryptography - the procedures, processes, methods, etc., of making and using secret writing, as codes or ciphers.

Ex: The process where you take your message and encode it using a key you make up. your sentence = yana is awesome your key = +3Encoded message = bdqd lv dzhvrph

• Cryptanalysis - the procedures, processes, methods, etc., used to translate or interpret secret writings, as codes and ciphers, for which the key is unknown.

Ex: encrypted segment = DEF cryptanalysis is the process where you go from the encrypted segment “DEF” to the decrypted segment “ABC” without using the key.

Terms (cont.)• Public key = in cryptography, a

value associated with a particular person and used to decrypt messages from that person or encrypt messages to him/her.

• Ex: key can be anything you make up, it could be as simple as encryption = letter +3, or more complicated like encryption = letter +3 -2 *3 /2.

• PROJECT PROGRESS• Main project is a hill cipher.

Which is a more complicated cipher which involves a two by two matrix.

Programming Example• Caesar cipher:

• #include<stdio.h>#define SIZE 10int main(){  int i=0;  char z, x[SIZE], c[SIZE]={0};  printf("Enter a 10 character message:  ");

  while(i<10){    c[i]=getchar();    i++;  }  i=0;   

while(i<10){    x[i]=c[i]+3;    printf("%c", x[i]);    i++;  }

printf("\n\n");  i=0;

  while(i<10){      z=x[i]-3;      i++;      printf("%c", z);    }        printf("\n");

  return 0;}

Quiz• 1) What is the difference between cryptology and

cryptography?

• 2) What is the main use for cryptology?

• 3) Draw how public key is used.

• 4) What would the encoded message of Yana be if the key is +4?

References• Spam and the ongoing battle for the inbox.

Communications of the ACM, Volume 50, #2 (2007), pages 24-33.Joshua Goodman, Gordon V. Cormack, David Heckerman.

• Textbook: Invitation to computer science java versionEdition 3, Schneider, copyright 07. pages 600-607

• An overview of cryptography. Gary C. Kessler, may 1998 (23 January 2009). (website) www.garykessler.net/library/crypto.html#purpose