加密/解密程序无法正常运行 [英] Encryption/decryption program not working properly

问题描述

我正在尝试构建一个程序，该程序将ascii值从32到126的字符转换为9个空格以对其进行加密.然后我想解密它.它可以成功解密大多数值，但最后一组则不能.这是我的代码如下:

I am trying to build a program that takes the characters with ascii values from 32 to 126 and shifting them over by 9 spaces to encrypt them. Then I want to decrypt it. It successfully decrypts most of the values but the last bunch do not. Here's my code below:

public static void main(String[] args) {

    final int SIZE = 95; // total # of ascii vals being used
    int[] availableChars = new int[SIZE];
    int[] ePhrase = new int[SIZE];
    int[] dePhrase = new int[SIZE];

    for(int i = 0; i < SIZE; i++){
        availableChars[i] = (i + 32);
    }

    for(int i = 0; i < SIZE; i++){
        ePhrase[i] = encrypt(availableChars[i] - 32);
    }

    for(int i = 0; i < SIZE; i++){
        dePhrase[i] = decrypt(ePhrase[i] - 32);
    }
    System.out.print("\n");

    for(int i = 0; i < SIZE; i++){
        System.out.print(i + " ");
    }
    System.out.print("\n");

    for(int i = 0; i < SIZE; i++){
        System.out.print((char)availableChars[i] + " ");
        if(i >= 10){
            System.out.print(" ");
        }
    }

    System.out.print("\n");

    for(int i = 0; i < SIZE; i++){
        System.out.print((char)ePhrase[i] + " ");
        if(i >= 10){
            System.out.print(" ");
        }
    }   

    System.out.print("\n");

    for(int i = 0; i < SIZE; i++){
        System.out.print((char)dePhrase[i] + " ");
        if(i >= 10){
            System.out.print(" ");
        }
    }

}

public static int encrypt(int val){
    return ((val + 9) % 94) + 32;
}

public static int decrypt(int val){
    return ((val - 9) % 94) + 32;
}

推荐答案

除了两个小问题，您的算法还可以.第一个缺陷是模运算必须考虑字母的所有字符，即95，而不是Willis在其回答中已经解释的94.

Apart from two minor issues your algorithm is OK. The first flaw is that the modulo-operation must consider all characters of the alphabet and that is 95 instead of 94 as already explained by Willis in his answer.

第二个问题是您使用了错误模运算符.在解密期间，(val - 9)项可能变为负数.但是，对于负数，模运算的数学定义不同于许多编程语言(包括Java)中的定义.在凯撒密码算法中，数学模运算符是引用的，因此必须在实现中使用.另请参阅:使用原始128 ASCII表使用仿射密码对字符串进行加密/解密

The second problem is that you use a wrong modulo-operator. During decryption the term (val - 9) can become negative. However, for negative numbers the mathematical definition of the modulo-operation differs from the definition in many programming languages (including Java). In the Caesar-cipher-algorithm the mathematical modulo-operator is referred to and thus, has to be used in the implementation. See also: Encrypting/Decrypting a string using a Affine cipher using the original 128 ASCII table

可以使用Java模运算符%定义数学模运算符，如下所示:

The mathematical modulo-operator can be defined in terms of the Java modulo-operator % as follows:

private static int mod(int a, int b) {
    return ((a % b) + b) % b;
}

或者，可以使用方法int Math.floorMod(int a, int b).另请参见: https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Math.html#floorMod(int，int)

Alternatively, the method int Math.floorMod(int a, int b) can be used. See also: https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Math.html#floorMod(int,int)

要使用此mod运算符(以及适当的除数95)替换为encrypt-方法

To use this mod-operator (and also the proper divisor 95) replace in your encrypt-method

return ((val + 9) % 94) + 32;

使用

return mod(val + 9, 95) + 32;

以及您的decrypt方法

return ((val - 9) % 94) + 32;

使用

return mod(val - 9, 95) + 32;

然后输出变为:

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 
  ! " # $ % & ' ( ) *  +  ,  -  .  /  0  1  2  3  4  5  6  7  8  9  :  ;  <  =  >  ?  @  A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z  [  \  ]  ^  _  `  a  b  c  d  e  f  g  h  i  j  k  l  m  n  o  p  q  r  s  t  u  v  w  x  y  z  {  |  }  ~  
) * + , - . / 0 1 2 3  4  5  6  7  8  9  :  ;  <  =  >  ?  @  A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z  [  \  ]  ^  _  `  a  b  c  d  e  f  g  h  i  j  k  l  m  n  o  p  q  r  s  t  u  v  w  x  y  z  {  |  }  ~     !  "  #  $  %  &  '  (  
  ! " # $ % & ' ( ) *  +  ,  -  .  /  0  1  2  3  4  5  6  7  8  9  :  ;  <  =  >  ?  @  A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z  [  \  ]  ^  _  `  a  b  c  d  e  f  g  h  i  j  k  l  m  n  o  p  q  r  s  t  u  v  w  x  y  z  {  |  }  ~  

现在，纯文本和解密文本匹配，并且在加密文本中，纯文本的所有字符都移位了9.

Now, plain and decrypted text match and all characters of the plain text are shifted by 9 in the encrypted text.

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