用CaesarCipherBreaker拆分字符串 [英] Splitting a string with CaesarCipherBreaker
问题描述
如何为此示例添加代码,以创建一个CaesarCipherBreaker方法,该方法将加密的邮件分为两个键。到目前为止,我已经写下了这么多的东西:
How would I add code to this example for creating a CaesarCipherBreaker method that splits the encrypted message by two keys. So far I have this much written down:
import edu.duke.*;
public class TestCaesarCipherTwo {
public int[] countOccurrencesOfLetters(String message) {
//snippet from lecture
String alph = "abcdefghijklmnopqrstuvwxyz";
int[] counts = new int[26];
for (int k=0; k < message.length(); k++) {
char ch = Character.toLowerCase(message.charAt(k));
int dex = alph.indexOf(ch);
if (dex != -1) {
counts[dex] += 1;
}
}
return counts;
}
public int maxIndex(int[] values) {
int maxDex = 0;
for (int k=0; k < values.length; k++) {
if (values[k] > values[maxDex]) {
maxDex = k;
}
}
return maxDex;
}
public String halfOfString(String message, int start) {
StringBuilder halfString = new StringBuilder();
for (int index=start;index < message.length();index += 2) {
halfString.append(message.charAt(index));
}
return halfString.toString();
}
public void simpleTests() {
FileResource fileResource = new FileResource();
String fileAsString = fileResource.asString();
CaesarCipherTwoKeys cctk = new CaesarCipherTwoKeys(17, 3);
String encrypted = cctk.encrypt(fileAsString);
System.out.println("Encrypted string:\n"+encrypted);
String decrypted = cctk.decrypt(encrypted);
System.out.println("Decrypted string:\n"+decrypted);
String blindDecrypted = breakCaesarCipher(encrypted);
System.out.println("Decrypted string using breakCaesarCipher():\n"+blindDecrypted);
}
public String breakCaesarCipher(String input) {
int[] freqs = countOccurrencesOfLetters(input);
int freqDex = maxIndex(freqs);
int dkey = freqDex - 4;
if (freqDex < 4) {
dkey = 26 - (4-freqDex);
}
CaesarCipherTwoKeys cctk = new CaesarCipherTwoKeys(dkey);
return cctk.decrypt(input);
}
}
警告:我也有一个构造函数错误CaesarCipherTwoKeys中的CaesarCipherTwoKeys不能应用于给定的类型; CaesarCipherTwoKeys(CaesarCipherTwoKeys(dkey); 说明 CaesarCipherTwoKeys cctk =需要int,int;发现int ...
。
WARNING: I also have a constructor error on this line CaesarCipherTwoKeys cctk = new CaesarCipherTwoKeys(dkey);
stating CaesarCipherTwoKeys in class CaesarCipherTwoKeys cannot be applied to given types; required int,int; found int...
.
breakCaesarCipher方法现在只显示出一个键,而不是两个。我应该如何编写一个分割加密字符串的方法,找出用于解密的两个密钥。
The breakCaesarCipher method I have now only figures out one key, not two. How should I go about writing a method that splits an encrypted string, figuring out two keys used for decryption.
推荐答案
如果我正确理解你的代码,你可以直接调用你的 halfOfString
(两次)获得密文的两个部分,然后使用通常的方法分别在两个部分上打破一个Ceaser-Cipher。
If I understand your Code correctly, you could just call your halfOfString
(two times) to get the two parts of the ciphertext and then use your usual approach to breaking a Ceaser-Cipher on both parts separately.
您的错误似乎结果从两键加密(不出意外)两个键的事实。你应该给他们两个构造函数。
Your error seems to result from the fact that the two-key-encryption expects (unsurprisingly) two keys. You should give them both to the constructor.
public String breakCaesarCipher(String input) {
String in_0 = halfOfString(input, 0);
String in_1 = halfOfString(input, 1);
// Find first key
// Determine character frequencies in ciphertext
int[] freqs_0 = countOccurrencesOfLetters(in_0);
// Get the most common character
int freqDex_0 = maxIndex(freqs_0);
// Calculate key such that 'E' would be mapped to the most common ciphertext character
// since 'E' is expected to be the most common plaintext character
int dkey_0 = freqDex_0 - 4;
// Make sure our key is non-negative
if (dkey_0 < 0) {
dkey_0 = dkey_0+26;
}
// Find second key
int[] freqs_1 = countOccurrencesOfLetters(in_1);
int freqDex_1 = maxIndex(freqs_1);
int dkey_1 = freqDex_1 - 4;
if (freqDex_1 < 4) {
dkey_1 = dkey_1+26;
}
CaesarCipherTwoKeys cctk = new CaesarCipherTwoKeys(dkey_0, dkey_1);
return cctk.decrypt(input);
}
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