I discovered that in java does not support 32 but integers. I had errors that i was getting when I had it in that form. So I switched over to BigInteger think it would fix this problem. So I kept on using BigInteger through the left and right shifting. Now i'm facing the problem of not getting the right output.
I'm using BigInteger to store a 128 byte key. But when running my code it's giving me the wrong output. And what i read was that it is possible to use masking which would solve this issue.
What I have tried:
when inputting the plaintText as: "0x0123456789ABCDEF"
Output is:
Original Plain Text:0x0123456789ABCDEF
CipherText:0xa0761126d09724fd
Decrypted CipherText is:0x8d5a4a234b3c6720
But when i input: 0x123456789ABCDEF
The output is:
Invalid block size!
Original Plain Text:0x123456789ABCDEF
CipherText:null
What am I doing wrong?
Here's my code:
import java.math.BigInteger;
public class TEA {
BigInteger [] K ; //128 bits key
private String plainText;
public static final BigInteger delta = new BigInteger("9e3779b9",16);
//constructor receives a string of plaintext and 128 bit key in hexadecimal
public TEA(String plainText, String key)
{
parseKey(key);
}
//constructor receives a hexadecimal
public TEA(String key)
{
parseKey(key);
}
//parses a 128 bit key, given in hexadecimal form, and store its value in 4 integers (total of 128 bits),
private void parseKey(String key)
{
if(key.substring(0,2).equals("0x"))
key= key.substring(2);
//validating input
if(key.length() != 32)
{
System.out.println("Invalid key size!");
return;
}
//dividing the key into 4 strings
String[] kStr = new String[4];
int index=-1;
for(int i=0; i<key.length(); i++)
{
if(i%8 == 0)
{
index++;
kStr[index]="";
}
kStr[index] = kStr[index] + key.charAt(i);
}
//converting the 4 hex strings into 4 integers
K= new BigInteger[4];
for(int i=0; i<4; i++)
K[i] = new BigInteger(kStr[i], 16);
}
//receives a plaintext block of 64 bits in hexadecimal to be encrypted
//returns the cipher block
String encryptBlock(String plainTextBlock)
{
if(plainTextBlock.substring(0,2).equals("0x"))
plainTextBlock= plainTextBlock.substring(2);
//validating input
if(plainTextBlock.length()!=16)
{
System.out.println("Invalid block size!");
return null;
}
//separating the string block into left and right blocks
String LStr = plainTextBlock.substring(0, 8); //left block (32 bit)
String RStr = plainTextBlock.substring(8); //right block (32 bit)
//converting left and right blocks to integers
BigInteger L = new BigInteger(LStr, 16);
BigInteger R = new BigInteger(RStr, 16);
BigInteger sum= new BigInteger("0");
//32 rounds
for(int i=0; i<32; i++)
{
sum = sum.add(delta);
L= sum(L, (sum(shiftLeft(R,4),K[0])) .xor(sum(R,sum)) .xor(sum(shiftRight(R,5),K[1]))) ;
R= sum(R, (sum(shiftLeft(L,4),K[2])) .xor(sum(L,sum)) .xor(sum(shiftRight(L,5),K[3]))) ;
//R= R.add( (shiftLeft(R,4).add(K[2])).xor(L.add(sum)).xor(shiftRight(L,5).add(K[3])) );
}
//joining back the blocks as hex
String cipherBlock = "0x"+L.toString(16)+R.toString(16)+"";
return cipherBlock;
}
//receives a ciphertext block of 64 bits in hexadecimal to be decrypted
//returns the plaintext block
String decryptBlock(String cipherBlock)
{
if(cipherBlock.substring(0,2).equals("0x"))
cipherBlock= cipherBlock.substring(2);
//validating input
if(cipherBlock.length()!=16)
{
System.out.println("Invalid block size!");
return null;
}
//separating the string block into left and right blocks
String LStr = cipherBlock.substring(0, 8); //left block (32 bit)
String RStr = cipherBlock.substring(8); //right block (32 bit)
//converting left and right blocks to integers
BigInteger L = new BigInteger(LStr, 16);
BigInteger R = new BigInteger(RStr, 16);
BigInteger sum= shiftLeft(delta,5);
//32 rounds
for(int i=0; i<32; i++)
{
R= subtract(R, (sum(shiftLeft(L,4),K[2])) .xor(sum(L,sum)) .xor(sum(shiftRight(L,5),K[3]))) ;
L= subtract(L, (sum(shiftLeft(R,4),K[0])) .xor(sum(R,sum)) .xor(sum(shiftRight(R,5),K[1]))) ;
//R= R.subtract( (L.shiftLeft(4).add(K[2])).xor(L.add(sum)).xor(L.shiftRight(5).add(K[3])) );
//L= L.subtract( (R.shiftLeft(4).add(K[0])).xor(R.add(sum)).xor(R.shiftRight(5).add(K[1])) );
sum = sum.subtract(delta);
}
//joining back the blocks as hex
String plainTextBlock = "0x"+L.toString(16)+R.toString(16)+"";
return plainTextBlock;
}
private BigInteger shiftLeft(BigInteger x, int steps)
{
BigInteger shifted=null;
boolean negative =false;
String xStr = x.toString(2);
//removing negative sign while shifting (currently)
if(xStr.charAt(0)=='-')
{
negative= true;
xStr = xStr.substring(1);
}
int additionalSize = 32- xStr.length();
for(int i=0; i<additionalSize; i++)
xStr= "0"+xStr;
for(int i=0; i<steps; i++)
{
xStr = xStr.substring(1);
xStr = xStr+"0";
}
//one last addition of negative sign if the number is negative
if(negative==true)
xStr= "-"+xStr;
//System.out.println(xStr);
shifted = new BigInteger(xStr,2);
return shifted;
}
private BigInteger shiftRight(BigInteger x, int steps)
{
BigInteger shifted=null;
boolean negative = false;
String xStr = x.toString(2);
//removing negative sign while shifting (currently)
if(xStr.charAt(0)=='-')
{
negative= true;
xStr = xStr.substring(1);
}
int additionalSize = 32- xStr.length();
for(int i=0; i<additionalSize; i++)
xStr= "0"+xStr;
for(int i=0; i<steps; i++)
{
xStr = xStr.substring(0,xStr.length()-1);
xStr = "0"+xStr;
}
//one last addition of negative sign if the number is negative
if(negative==true)
xStr= "-"+xStr;
shifted = new BigInteger(xStr,2);
return shifted;
}
private BigInteger sum(BigInteger a, BigInteger b)
{
BigInteger sum = a.add(b);
String sumStr = sum.toString(2);
if(sumStr.length()>32)
{
int diff = sumStr.length()- 32;
sumStr = sumStr.substring(diff);
}
BigInteger newSum = new BigInteger(sumStr,2);
return newSum;
}
private BigInteger subtract(BigInteger a, BigInteger b)
{
BigInteger sub = a.subtract(b);
String subStr = sub.toString(2);
if(subStr.length()>32)
{
int diff = subStr.length()- 32;
subStr = subStr.substring(diff);
}
BigInteger newSub = new BigInteger(subStr,2);
return newSub;
}
public static void main(String[] args)
{
String plainText="0x0123456789ABCDEF";
String key= "0xA56BABCD00000000FFFFFFFFABCDEF01";
TEA tea = new TEA(key);
String cipherText = tea.encryptBlock(plainText);
System.out.println("Original Plain Text:"+plainText);
System.out.println("CipherText:"+cipherText);
System.out.println("Decrypted CipherText is:"+tea.decryptBlock(cipherText));
}
}
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