HillCipher.java

class hillCipher {
/* 3x3 key matrix for 3 characters at once */
public static int[][] keymat = new int[][] { { 1, 2, 1 }, { 2, 3, 2 },
{ 2, 2, 1 } }; /* key inverse matrix */
public static int[][] invkeymat = new int[][] { { -1, 0, 1 }, { 2, -1, 0 }, { -2, 2, -1
} };
public static String key = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
private static String encode(char a, char b, char c)
{ String ret = "";
int x, y, z;
int posa = (int) a - 65;
int posb = (int) b -
65; int posc = (int) c -
65;
x = posa * keymat[0][0] + posb * keymat[1][0] + posc * keymat[2]
[0]; y = posa * keymat[0][1] + posb * keymat[1][1] + posc *
keymat[2][1]; z = posa * keymat[0][2] + posb * keymat[1][2] + posc *
keymat[2][2]; a = key.charAt(x % 26);
b = key.charAt(y % 26);
c = key.charAt(z % 26); ret = 
"" + a + b + c; return ret;
}
private static String decode(char a, char b, char c)
{ String ret = "";
int x, y, z;
int posa = (int) a - 65;
int posb = (int) b -
65; int posc = (int) c -
65;
x = posa * invkeymat[0][0] + posb * invkeymat[1][0] + posc * invkeymat[2]
[0];
y = posa * invkeymat[0][1] + posb * invkeymat[1][1] + posc * invkeymat[2]
[1];
z = posa * invkeymat[0][2] + posb * invkeymat[1][2] + posc * invkeymat[2]
[2];
a = key.charAt((x % 26 < 0) ? (26 + x % 26) : (x % 26));
b = key.charAt((y % 26 < 0) ? (26 + y % 26) : (y %
26)); c = key.charAt((z % 26 < 0) ? (26 + z % 26) : (z %
26)); ret = "" + a + b + c;
return ret;
}
public static void main(String[] args) throws java.lang.Exception
{ String msg;
String enc =
""; String dec
= ""; int n;
msg = ("SecurityLaboratory");
System.out.println("simulation of Hill Cipher\n------------------------");
System.out.println("Input message : " + msg);
msg = msg.toUpperCase();
msg = msg.replaceAll("\\s", "");
/* remove spaces */ n = msg.length() % 3;
/* append padding text X */ if (n != 0)
{ for (int i = 1; i <= (3 - n); i++) {
msg += 'X';
}}
System.out.println("padded message : " + msg);
char[] pdchars = msg.toCharArray();
for (int i = 0; i < msg.length(); i += 3) {
enc += encode(pdchars[i], pdchars[i + 1], pdchars[i + 2]);
}
System.out.println("encoded message : " +
enc); char[] dechars = enc.toCharArray();
for (int i = 0; i < enc.length(); i += 3) {
dec += decode(dechars[i], dechars[i + 1], dechars[i + 2]);
}
System.out.println("decoded message : " + dec);
}
}
OUTPUT:
Simulating Hill Cipher
Input Message : SecurityLaboratory
Padded Message : SECURITYLABORATORY
Encrypted Message : EACSDKLCAEFQDUKSXU
Decrypted Message : SECURITYLABORATORY