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# 8606 ins prac 1.docx

ins sem 6 pillais college

ins sem 6 pillais college

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### 8606 ins prac 1.docx

1. 1. [Type here] [Type here] Khushal Choudhary 8606 PRACTICAL NO. 1 Aim: Implementing Substitution Ciphers a) Caesar Cipher Code: // Practical 1 A import java.util.Scanner; public class practical1a { int total_alphabets=26,key=3; String encrypted=" ",decrypted=" "; char ch; public String encrypt (String plain) { for(int i=0;i<plain.length();i++) { ch=plain.charAt(i); if(ch==' ') encrypted+="-"; else if(ch>='A' && ch<='Z') { if(ch<='Z'-key) { encrypted+=String.valueOf((char)(ch+key)); } else { encrypted+=String.valueOf((char)(ch- (total_alphabetskey))); } } else { encrypted+=String.valueOf(ch); } } return encrypted; } public String decrypt (String cipher) { for(int i=0;i<cipher.length();i++) { ch=cipher.charAt(i); if(ch==' ') decrypted+="-"; else if(ch>='A' && ch<='Z') { if(ch>='A'+key) {
2. 2. [Type here] [Type here] Khushal Choudhary 8606 decrypted+=String.valueOf((char)(ch-key)); } else { decrypted+=String.valueOf((char)(ch+(total_alphabetskey))); } } else { decrypted+=String.valueOf(ch); } } return decrypted; } public static void main(String[] args) { String plaintext, ciphertext; practical1a cc= new practical1a(); System.out.println("Enter text"); plaintext=new Scanner(System.in).nextLine().toUpperCase(); ciphertext=cc.encrypt(plaintext); System.out.println("Encrypted text="+ciphertext); plaintext=cc.decrypt(ciphertext); System.out.println("Decrypted text="+plaintext); } } Output: Modified Caesar Cipher Code:
3. 3. [Type here] [Type here] Khushal Choudhary 8606 } } else { decrypted+=String.valueOf(ch); } } return decrypted; } public static void main(String[] args) { String plaintext, ciphertext; int key; practical1b cc= new practical1b(); System.out.println("Enter text"); plaintext=new Scanner(System.in).nextLine().toUpperCase(); System.out.println("Enter key "); key=new Scanner(System.in).nextInt(); ciphertext=cc.encrypt(plaintext,key); System.out.println("Encrypted text="+ciphertext); plaintext=cc.decrypt(ciphertext,key); System.out.println("Decrypted text="+plaintext); } } Output: Monoalphabetic
4. 4. [Type here] [Type here] Khushal Choudhary 8606 Code: } Output: d) Poly-Alphabetic Code: import java.util.*; public class Poly { public static void main(String[]args) { String plaintext="HOWAREYOU"; String secretkey="HELLOHELL"; System.out.println("Plain text before encryption:"+plaintext); String encryptedtext=encrypt(plaintext,secretkey); System.out.println("Encrypted text after encryption:"+encryptedtext); String decryptedtext=decrypt(encryptedtext,secretkey); System.out.println("Decrypted text after decryption:"+decryptedtext); } private static String encrypt(String plaintext, String secretkey) { StringBuffer encryptedString=new StringBuffer(); int encryptedInt; for(int i=0;i<plaintext.length();i++) { int plaintextInt=(int)(plaintext.charAt(i)); int secretkeyInt=(int)(secretkey.charAt(i)); encryptedInt=(plaintextInt+secretkeyInt)%26; encryptedString.append((char)((encryptedInt)+(int)'A')); } return encryptedString.toString(); } private static String decrypt(String decryptedtext, String secretkey) {
5. 5. [Type here] [Type here] Khushal Choudhary 8606 StringBuffer decryptedString=new StringBuffer(); int decryptedInt; for(int i=0;i<decryptedtext.length();i++) { int decryptedtextInt=(int)(decryptedtext.charAt(i)); int secretkeyInt=(int)(secretkey.charAt(i)); decryptedInt=decryptedtextInt-secretkeyInt; if(decryptedInt<0) Output: