Implementation of Hill cipher in Java

// File name:HillCipher.java
import java.util.*;
class Basic{
  String allChar="ABCDEFGHIJKLMNOPQRSTUVWXYZ";
  int indexOfChar(char c)
 {
  for(int i=0;i < allChar.length();i++)
  {
   if(allChar.charAt(i)==c)
    return i;
  }
  return -1;
 }
 
 char charAtIndex(int pos)
 {
  return allChar.charAt(pos);
 }
}
class Hill{
    
        Hill(int block)
        {
            this.block=block;
        }
    
       Basic b1=new Basic();
       int block=2;
       int key[][]=new int[block][block];
       
       
       void keyInsert()throws Exception
       {
           Scanner scn=new Scanner(System.in);
           System.out.println("Enter key Matrix");
           for(int i=0;i < block;i++)
           {
                for(int j=0;j < block;j++)
                {
                    key[i][j]=scn.nextInt();
                } 
           }
       }
       
       void KeyInverseInsert()throws Exception
       {
           Scanner scn=new Scanner(System.in);
           System.out.println("Enter key Inverse Matrix:");
           for(int i=0;i < block;i++)
           {
                for(int j=0;j < block;j++)
                {
                    key[i][j]=scn.nextInt();
                } 
           }
       }
       
       String encryptBlock(String plain)throws Exception
       {
           plain=plain.toUpperCase();
           int a[][]=new int[block][1],sum=0;
           int cipherMatrix[][]=new int[block][1];
           String cipher="";
           
           for(int i=0;i < block;i++)
           {
               a[i][0]=b1.indexOfChar(plain.charAt(i));
           }
       
           
           for(int i=0;i < block;i++)
   {
    for(int j=0;j < 1;j++)
    {   
     for(int k=0;k < block;k++)
     {
      sum=sum+key[i][k]*a[k][j];
     }
     cipherMatrix[i][j] = sum%26;
     sum = 0;
    }
   }
          
           
           for(int i=0;i < block;i++)
           {
              cipher+=b1.charAtIndex(cipherMatrix[i][0]);
           }
           return cipher;
       }
       
       String encrypt(String plainText)throws Exception
       {
           String cipherText="";
            keyInsert();
           
            plainText=plainText.toUpperCase();
            
               int len=plainText.length();
          // System.out.println(plainText.substring(1,2+1));
           
               while(len%block!=0)
               {
                   plainText+="X";
                   System.out.println(len);
                   len=plainText.length();
               }
           
           
           for(int i=0;i < len-1;i=i+block)
           {
              cipherText+=encryptBlock(plainText.substring(i,i+block));
              cipherText+=" "; 
           }
           return cipherText;
       }
       
        String decryptBlock(String cipher)throws Exception
       {
           cipher=cipher.toUpperCase();
           int a[][]=new int[block][1],sum=0;
           int plainMatrix[][]=new int[block][1];
           String plain="";
           
           for(int i=0;i < block;i++)
           {
               a[i][0]=b1.indexOfChar(cipher.charAt(i));
           }
       
           
           for(int i=0;i < block;i++)
   {
    for(int j=0;j < 1;j++)
    {   
     for(int k=0;k < block;k++)
     {
      sum=sum+key[i][k]*a[k][j];
     }
                                        while(sum < 0)
                                        {
                                              sum+=26;
                                        }
     plainMatrix[i][j] = sum;
     sum = 0;
    }
   }
          
           
           for(int i=0;i < block;i++)
           {
              plain+=b1.charAtIndex(plainMatrix[i][0]);
           }
           return plain;
       }
       
       String Decrypt(String cipherText)throws Exception
       {
           String plainText="";
           KeyInverseInsert();
           cipherText=cipherText.replaceAll(" ", "");
           
            cipherText=cipherText.toUpperCase();
            
               int len=cipherText.length(); 

           for(int i=0;i < len-1;i=i+block)
           {
              plainText+=decryptBlock(cipherText.substring(i,i+block));
              plainText+=" "; 
           }
           return plainText;
       }
       
}

class HillCipher{
       public static void main(String args[])throws Exception
       {
           String plainText,cipherText;  
           int block;
           Scanner scn=new Scanner(System.in);
          
           System.out.println("Enter plain-text:");
           plainText=scn.nextLine();
           
           System.out.println("Enter block size of matrix:");
           block=scn.nextInt();
           Hill hill=new Hill(block);
           
           plainText=plainText.replaceAll(" ", "");
           cipherText= hill.encrypt(plainText);
           
           System.out.println("Encrypted Text is:\n"+cipherText);
           
           String decryptedText= hill.Decrypt(cipherText);
           System.out.println("Decrypted Text is:\n"+decryptedText);
           
                    
       }
}

OUTPUT

Enter plain-text:
meet
Enter block size of matrix:
2
Enter key Matrix
3 1
5 2
Encrypted Text is:
OQ FG
Enter key Inverse Matrix:
2 -1
-5 3
Decrypted Text is:
ME ET