FourSquareCipher

package ie.gmit.dip;

public class FourSquareCipher {
	private char[][] matrix = {
			{'A', 'B', 'C', 'D', 'E', 'Z', 'G', 'P', 'T', 'F'},
			{'F', 'G', 'H', 'I', 'K', 'O', 'I', 'H', 'M', 'U'},
			{'L', 'M', 'N', 'O', 'P', 'W', 'D', 'R', 'C', 'N'},
			{'Q', 'R', 'S', 'T', 'U', 'Y', 'K', 'E', 'Q', 'A'},
			{'V', 'W', 'X', 'Y', 'Z', 'X', 'V', 'S', 'B', 'L'},
			{'M', 'F', 'N', 'B', 'D', 'A', 'B', 'C', 'D', 'E'},
			{'C', 'R', 'H', 'S', 'A', 'F', 'G', 'H', 'I', 'K'},
			{'X', 'Y', 'O', 'G', 'V', 'L', 'M', 'N', 'O', 'P'},
			{'I', 'T', 'U', 'E', 'W', 'Q', 'R', 'S', 'T', 'U'},
			{'L', 'Q', 'Z', 'K', 'P', 'V', 'W', 'X', 'Y', 'Z'}
		};
			
	public FourSquareCipher() {
		
	}

	public FourSquareCipher (char[][] setMatrix){
		this.matrix=setMatrix;
	}
			
	

	public void setNewKeyUpperRight(char[] key){ 
		  int i=0;
		  while(i<key.length) {
			  // each character in the upperRight quadrant of the matrix array rows 0-5, columns 5-10
			  // is then replaced with key[i] the character at index i from the passed in array and i is incremented.
			  for(int row = 0;row<5;row++) {
				  for(int col = 5;col<10;col++) {
					matrix[row][col] = key[i];
					i++;
				  }
			  }
		        
		  }
		  
	 }
	  
	public char[][] setNewKeyBottomLeft(char[] key){ 
		  int i=0;
		  while(i<key.length) {
			  // each character in the bottom left quadrant of the matrix array rows 0-5, columns 5-10
			  // is then replaced with key[i] the character at index i from the passed in array and i is incremented.
			  for(int row = 5;row<10;row++) {
				  for(int col = 0;col<5;col++) {
					matrix[row][col] = key[i];
					i++;
				  }
			  }
		  }
		  return matrix;
	 } 
	  
	public void printmulti() {
			for(int row=0;row<matrix.length;row++) {
				System.out.print("{");
				for(int col = 0;col<matrix[row].length;col++) {
					System.out.print(" " +matrix[row][col]+ " ,");
				}
				System.out.println("}");
			}
			
		}
	  
	public String encrypt(String[] couples) {
		char plainLet1, plainLet2;
		// a new stringbuilder object is created
		StringBuilder ciphertext = new StringBuilder();
		// the passed string array is traversed
		for(int i=0;i<couples.length;i++) {
			// as long as the bigram-string at each index of the array is not null or full of white space then:
			if (couples[i] != null && couples[i].trim().length()>0) {
				// char variables are assigned the plain-text char's at index 0 and 1 of the bigram-string
				plainLet1 = couples[i].charAt(0);
				plainLet2 = couples[i].charAt(1);
				// the encrypted bigram string of the two original plain-text chars is appended to the stringbuilder
				ciphertext.append(encryptbigrams(plainLet1, plainLet2));
			}		
			
		}
		
		// the completed stringbuilder is then returned as a string.
		
		return ciphertext.toString();
	}
	
	public String encryptbigrams (char a, char b) {
		int xFirst = 0, yFirst = 0, xSecond = 0, ySecond = 0; 
		StringBuilder cipherbigram = new StringBuilder();
		// the first character 'a' of the bigram locates its position in the upper-left portion of the cipher square
		
			for(int row1=0;row1<5;row1++) {
				for(int col1=0;col1<5;col1++) {
					if(matrix[row1][col1]==a) {
						// variables are used to store the index no's of the row and column of the char locations in the matrix array.
						xFirst = row1;
						yFirst = col1;
					}
				}
			}
			// the second character 'b' of the bigram locates its position in the lower-right portion of the cipher square	
			for(int row4=5;row4<10;row4++) {
				for(int col4=5;col4<10;col4++) {
					if(matrix[row4][col4]==b) {
						// variables are used to store the index no's of the row and column of the char locations in the matrix array.
						xSecond = row4;
						ySecond = col4;
					}
				}
			}
			/* a stringbuilder then combines the intersection points at the intersection of the
			row of char 'a' above with the column of char 'b' above in the bottom right square and at the intersection of the
			column of char 'a' with the row of char 'b' */
			cipherbigram.append(matrix[xFirst][ySecond]).append(matrix[xSecond][yFirst]);
			
		// an encrypted bigram string is then returned to the encrypt method
		return cipherbigram.toString();
		
	}
	
	public String decrypt(String[] couples) {
		char encryptLet1, encryptLet2;
		StringBuilder plaintext = new StringBuilder();
		for(int i=0;i<couples.length;i++) {
			if (couples[i] != null && couples[i].trim().length()>0) {
				encryptLet1 = couples[i].charAt(0);
				encryptLet2 = couples[i].charAt(1);
				//
				plaintext.append(decryptbigrams(encryptLet1, encryptLet2));
			}		
			
		}
		//System.out.println(ciphertext.toString());
		return plaintext.toString();
	}	
	
	public String decryptbigrams (char a, char b) {
		int xFirst = 0, yFirst = 0, xSecond = 0, ySecond = 0; 
		StringBuilder cipherbigram = new StringBuilder();
		// the first character 'a' of the bigram locates its position in the upper-left portion of the cipher square
			for(int row2=0;row2<5;row2++) {
				for(int col2=5;col2<10;col2++) {
					if(matrix[row2][col2]==a) {
						// variables are used to store the index no's of the row and column of the char locations in the matrix array.
						xFirst = row2;
						yFirst = col2;
					}
				}
			}
			// the second character 'b' of the bigram locates its position in the lower-right portion of the cipher square	
			for(int row3=5;row3<10;row3++) {
				for(int col3=0;col3<5;col3++) {
					if(matrix[row3][col3]==b) {
						// variables are used to store the index no's of the row and column of the char locations in the matrix array.
						xSecond = row3;
						ySecond = col3;
					}
				}
			}
			/* a stringbuilder then combines the intersection points at the intersection of the
			row of char 'a' above with the column of char 'b' above in the bottom right square and at the intersection of the
			column of char 'a' with the row of char 'b' */
			cipherbigram.append(matrix[xFirst][ySecond]).append(matrix[xSecond][yFirst]);
			
			
		// a bigram string is then returned to encrypt method
		return cipherbigram.toString();
	}
	 
	
}