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34
src/main/java/ch/fhnw/kry/CTR.java
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34
src/main/java/ch/fhnw/kry/CTR.java
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package ch.fhnw.kry;
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import java.util.Random;
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import java.util.concurrent.ThreadLocalRandom;
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public class CTR {
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private final SPN spn = new SPN();
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private final int iv;
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private final int key;
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public CTR(int key) {
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this.iv = generateIV();
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this.key = key;
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}
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public int getIV() {
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return iv;
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}
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public int generateIV() {
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Random random = ThreadLocalRandom.current();
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byte[] r = new byte[2];
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random.nextBytes(r);
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return r[0] << 8 & r[1];
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}
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public int decrypt(int block, int idx) {
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int e = (iv + idx) % (1 << 16);
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e = spn.decryptBlock(key, e);
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return block ^ e;
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}
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}
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49
src/main/java/ch/fhnw/kry/Decrypt.java
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49
src/main/java/ch/fhnw/kry/Decrypt.java
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package ch.fhnw.kry;
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import java.nio.charset.StandardCharsets;
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import static ch.fhnw.kry.Main.BLOCK_LENGTH;
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public class Decrypt {
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public String decrypt(String keyString, String chiffre) {
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int key = Integer.parseInt(keyString, 2);
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var ctr = new CTR(key);
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int[] data = strToArray(chiffre);
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byte[] decryptedData = new byte[data.length * 2];
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for (int i = 0; i < data.length; i++) {
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int block = data[i];
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int decryptedBlock = ctr.decrypt(block, i);
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decryptedData[i * 2] = (byte)(decryptedBlock >>> 8);
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decryptedData[i * 2 + 1] = (byte)(decryptedBlock & 0x0000_00FF);
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}
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String decryptedString = new String(decryptedData, StandardCharsets.US_ASCII);
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return decryptedString;
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}
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/**
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* Convert a bit string into an integer array.
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*
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* Because later we only ever look at the lower 16 bits,
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* we stuff every block of 16 bits into the lower half of an int
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* (meaning the igh 16 bits of the ints in the array are always 0).
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*
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* @param bits Bit string. Its length must be a multiple of 16.
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* @return int array, with every int's lower 16 bits set to 16 bits of the input string.
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*/
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public int[] strToArray(String bits) {
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int[] data = new int[bits.length() / BLOCK_LENGTH];
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for (int i = 0; i < data.length; i++) {
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int startIdx = i * BLOCK_LENGTH;
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String wordBits = bits.substring(startIdx, startIdx + BLOCK_LENGTH);
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int word = Integer.parseInt(wordBits, 2);
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data[i] = word;
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}
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return data;
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}
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}
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*/
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public class Main {
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private static final String KEY = "00111010100101001101011000111111";
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private static final String CHIFFRE =
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static final String KEY = "00111010100101001101011000111111";
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static final String CHIFFRE =
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"00000100110100100000101110111000000000101000111110001110011111110110000001010001010000111010000000010011011001110010101110110000";
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static final int BLOCK_LENGTH = 16;
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public static void main(String[] args) {
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}
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@ -3,6 +3,7 @@ package ch.fhnw.kry;
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import java.util.HashMap;
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import java.util.Map;
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import static ch.fhnw.kry.Main.BLOCK_LENGTH;
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import static java.util.Map.entry;
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public class SPN {
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@ -62,37 +63,9 @@ public class SPN {
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entry(15, 15)
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);
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private static final int BLOCK_LENGTH = 16;
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private static final int ROUNDS = 4;
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public String decrypt(int key, String chiffre) {
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return null;
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}
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/**
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* Convert a bit string into an integer array.
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*
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* Because later we only ever look at the lower 16 bits,
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* we stuff every block of 16 bits into the lower half of an int
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* (meaning the igh 16 bits of the ints in the array are always 0).
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*
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* @param bits Bit string. Its length must be a multiple of 16.
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* @return int array, with every int's lower 16 bits set to 16 bits of the input string.
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*/
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public int[] strToArray(String bits) {
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int[] data = new int[bits.length() / BLOCK_LENGTH];
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for (int i = 0; i < data.length; i++) {
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int startIdx = i * BLOCK_LENGTH;
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String wordBits = bits.substring(startIdx, startIdx + BLOCK_LENGTH);
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int word = Integer.parseInt(wordBits, 2);
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data[i] = word;
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}
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return data;
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}
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/**
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* Encrypt a block with the defined SPN.
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*
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20
src/test/java/ch/fhnw/kry/CTRTest.java
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20
src/test/java/ch/fhnw/kry/CTRTest.java
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package ch.fhnw.kry;
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import org.junit.jupiter.api.Test;
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import static org.junit.jupiter.api.Assertions.*;
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class CTRTest {
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@Test
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void generateIV() {
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var ctr = new CTR(0);
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int count = 0;
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while(count < Integer.MAX_VALUE) {
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int iv = ctr.generateIV();
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assert (iv < 1 << 16);
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count++;
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}
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}
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}
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src/test/java/ch/fhnw/kry/DecryptTest.java
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28
src/test/java/ch/fhnw/kry/DecryptTest.java
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package ch.fhnw.kry;
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import org.junit.jupiter.api.Test;
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import static ch.fhnw.kry.Main.CHIFFRE;
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import static ch.fhnw.kry.Main.KEY;
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import static org.junit.jupiter.api.Assertions.*;
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class DecryptTest {
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@Test
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void strToArray() {
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var decrypt = new Decrypt();
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String input = "00000100110100100000101110111000000000101000111110001110011111110110000001010001010000111010000000010011011001110010101110110000";
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int[] data = decrypt.strToArray(input);
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assertEquals(8, data.length);
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assertEquals(0x04D2, data[0]);
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assertEquals(0x2BB0, data[data.length - 1]);
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}
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@Test
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void decrypt() {
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var decrypt = new Decrypt();
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String decrypted = decrypt.decrypt(KEY, CHIFFRE);
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}
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}
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assertEquals(y, spn.encryptBlock(key, x));
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assertEquals(x, spn.decryptBlock(key, y));
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}
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@Test
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void strToArray() {
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var spn = new SPN();
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String input = "00000100110100100000101110111000000000101000111110001110011111110110000001010001010000111010000000010011011001110010101110110000";
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int[] data = spn.strToArray(input);
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assertEquals(8, data.length);
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assertEquals(0x04D2, data[0]);
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assertEquals(0x2BB0, data[data.length - 1]);
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}
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}
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