未越界时得到 ArrayIndexOutOfBoundException-解网

问：

我正在编写一个带有 128 位密钥的 AES 实现。在 else 块的最后一行抛出异常。

    private static int KEY_SIZE_IN_BYTE = 16;
    private static int EXPANDED_KEY_SIZE_IN_BYTE = 176;
    private static int BYTE_PER_WORD = 4;

private static byte[][] doKeyExpansion(byte[] keyByteArray) {
        int keySizeInWord = KEY_SIZE_IN_BYTE / BYTE_PER_WORD;
        int expandedKeySizeInWord = EXPANDED_KEY_SIZE_IN_BYTE / BYTE_PER_WORD;
        
        byte[][] result = new byte[expandedKeySizeInWord][BYTE_PER_WORD];
        
        for(int i = 0; i < keySizeInWord; i++) {
            for(int j = 0; j < BYTE_PER_WORD; j++) {
                result[i][j] = keyByteArray[i * BYTE_PER_WORD + j];
            }
        }
        
        for(int i = keySizeInWord; i < expandedKeySizeInWord; i++) {
            byte[] temp = new byte[BYTE_PER_WORD];
            
            // Rotate word if 4 divides i
            if(i % 4 == 0) {
                for(int j = 0; j < BYTE_PER_WORD; j++) {
                    temp[j] = result[i - 1][(j + 1) % BYTE_PER_WORD];
                }
            } else {
                for(int j = 0; j < BYTE_PER_WORD; j++) {
                    byte a = result[i - 1][j];
                    temp[j] = 1;
                    byte b = 5;
                    temp[j] = b;

                    // Exception is thrown if this is not commented
                    //temp[j] = a;
                }
            }
            
            // Substitute using Sbox
            for(int j = 0; j < BYTE_PER_WORD; j++) {
                temp[j] = substitueWithSbox(temp[j]);
            }
            
            // xor round constant
            byte[] roundConstant = { (byte) ROUND_CONSTANT_FIRST_BYTE[(i / BYTE_PER_WORD) - 1], 0, 0, 0}; 
            temp = xorWord(temp, roundConstant);
            
            result[i] = xorWord(temp, result[i - 4]);
        }
        
        return result;
    }

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: Index 3 out of bounds for length 3

当我像这样注释掉它时，代码运行良好，没有问题。我试图像上面的几行一样将它们分开，并且作业的两边都不会触发任何异常。我不知道为什么会这样。

有人可以帮忙吗？

我添加这个是为了帮助提供情况的细节。如果第 83 行没有注释，第 87 行就会抛出一个摘录（感谢@tgdavies他纠正了我）。把它注释掉，它就会起作用。这是我迄今为止看到的最令人困惑的事情。

import java.util.BitSet;

public class Duplicate {
    
    private static byte HEX_BASE = 16;

    private static int KEY_SIZE_IN_BYTE = 16;

    private static int EXPANDED_KEY_SIZE_IN_BYTE = 176;
    private static int BYTE_PER_WORD = 4;

    
    private static int[] SBOX = {
            0x63, 0x7C, 0x77, 0x7B, 0xF2, 0x6B, 0x6F, 0xC5, 0x30, 0x01, 0x67, 0x2B, 0xFE, 0xD7, 0xAB, 0x76,
            0xCA, 0x82, 0xC9, 0x7D, 0xFA, 0x59, 0x47, 0xF0, 0xAD, 0xD4, 0xA2, 0xAF, 0x9C, 0xA4, 0x72, 0xC0,
            0xB7, 0xFD, 0x93, 0x26, 0x36, 0x3F, 0xF7, 0xCC, 0x34, 0xA5, 0xE5, 0xF1, 0x71, 0xD8, 0x31, 0x15,
            0x04, 0xC7, 0x23, 0xC3, 0x18, 0x96, 0x05, 0x9A, 0x07, 0x12, 0x80, 0xE2, 0xEB, 0x27, 0xB2, 0x75,
            0x09, 0x83, 0x2C, 0x1A, 0x1B, 0x6E, 0x5A, 0xA0, 0x52, 0x3B, 0xD6, 0xB3, 0x29, 0xE3, 0x2F, 0x84,
            0x53, 0xD1, 0x00, 0xED, 0x20, 0xFC, 0xB1, 0x5B, 0x6A, 0xCB, 0xBE, 0x39, 0x4A, 0x4C, 0x58, 0xCF,
            0xD0, 0xEF, 0xAA, 0xFB, 0x43, 0x4D, 0x33, 0x85, 0x45, 0xF9, 0x02, 0x7F, 0x50, 0x3C, 0x9F, 0xA8,
            0x51, 0xA3, 0x40, 0x8F, 0x92, 0x9D, 0x38, 0xF5, 0xBC, 0xB6, 0xDA, 0x21, 0x10, 0xFF, 0xF3, 0xD2,
            0xCD, 0x0C, 0x13, 0xEC, 0x5F, 0x97, 0x44, 0x17, 0xC4, 0xA7, 0x7E, 0x3D, 0x64, 0x5D, 0x19, 0x73,
            0x60, 0x81, 0x4F, 0xDC, 0x22, 0x2A, 0x90, 0x88, 0x46, 0xEE, 0xB8, 0x14, 0xDE, 0x5E, 0x0B, 0xDB,
            0xE0, 0x32, 0x3A, 0x0A, 0x49, 0x06, 0x24, 0x5C, 0xC2, 0xD3, 0xAC, 0x62, 0x91, 0x95, 0xE4, 0x79,
            0xE7, 0xC8, 0x37, 0x6D, 0x8D, 0xD5, 0x4E, 0xA9, 0x6C, 0x56, 0xF4, 0xEA, 0x65, 0x7A, 0xAE, 0x08,
            0xBA, 0x78, 0x25, 0x2E, 0x1C, 0xA6, 0xB4, 0xC6, 0xE8, 0xDD, 0x74, 0x1F, 0x4B, 0xBD, 0x8B, 0x8A,
            0x70, 0x3E, 0xB5, 0x66, 0x48, 0x03, 0xF6, 0x0E, 0x61, 0x35, 0x57, 0xB9, 0x86, 0xC1, 0x1D, 0x9E,
            0xE1, 0xF8, 0x98, 0x11, 0x69, 0xD9, 0x8E, 0x94, 0x9B, 0x1E, 0x87, 0xE9, 0xCE, 0x55, 0x28, 0xDF,
            0x8C, 0xA1, 0x89, 0x0D, 0xBF, 0xE6, 0x42, 0x68, 0x41, 0x99, 0x2D, 0x0F, 0xB0, 0x54, 0xBB, 0x16
            };
    
    private static int[] ROUND_CONSTANT_FIRST_BYTE = { 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x1B, 0x36 };

    public static void main(String[] args) {
        String plaintextExample = "0123456789abcdeffedcba9876543210".toUpperCase();
        String keyExample = "0f1571c947d9e8590cb7add6af7f6798".toUpperCase();
        String ciphertextExample = "ff0b844a0853bf7c6934ab4364148fb9".toUpperCase();
        
        String plaintextExample2 = "0023456789abcdeffedcba9876543210".toUpperCase();
        String ciphertextExample2 = "612b89398d0600cde116227ce72433f0".toUpperCase();
        
        byte[] keyByteArray = convertKeyToByteArray(keyExample);
        byte[][] expandedKey = doKeyExpansion(keyByteArray);
        
//      for(int i = 0; i < 44; i++) {
//          for(int j = 0; j < 4; j++) {
//              System.out.print(Integer.toHexString(Byte.toUnsignedInt(expandedKey[i][j])));
//          }
//      }
        
        System.out.println("Done");
    }
    
    private static void testByteArray(byte[] toTest) {
        for(int i = 0; i < toTest.length; i++) {
            System.out.print(toTest[i]);
        }
        System.out.println();
    }

    private static byte[][] doKeyExpansion(byte[] keyByteArray) {
        int keySizeInWord = KEY_SIZE_IN_BYTE / BYTE_PER_WORD;
        int expandedKeySizeInWord = EXPANDED_KEY_SIZE_IN_BYTE / BYTE_PER_WORD;
        
        byte[][] result = new byte[expandedKeySizeInWord][BYTE_PER_WORD];
        
        for(int i = 0; i < keySizeInWord; i++) {
            for(int j = 0; j < BYTE_PER_WORD; j++) {
                result[i][j] = keyByteArray[i * BYTE_PER_WORD + j];
            }
        }
        
        for(int i = keySizeInWord; i < expandedKeySizeInWord; i++) {
            byte[] temp = new byte[BYTE_PER_WORD];
            
            // Rotate word if 4 divides i
            if(i % 4 == 0) {
                for(int j = 0; j < BYTE_PER_WORD; j++) {
                    temp[j] = result[i - 1][(j + 1) % BYTE_PER_WORD];
                }
            } else {
                for(int j = 0; j < BYTE_PER_WORD; j++) {
                    byte a = result[i - 1][j];    // line 83
                    temp[j] = 1;
                    byte b = 5;
                    temp[j] = b;
                    temp[j] = a;    // line 87
                }
            }
            
            // Substitute using Sbox
            for(int j = 0; j < BYTE_PER_WORD; j++) {
                temp[j] = substitueWithSbox(temp[j]);
            }
            
            // xor round constant
            byte[] roundConstant = { (byte) ROUND_CONSTANT_FIRST_BYTE[(i / BYTE_PER_WORD) - 1], 0, 0, 0}; 
            temp = xorWord(temp, roundConstant);
            
            result[i] = xorWord(temp, result[i - 4]);
        }
        
        return result;
    }

    private static byte[] xorWord(byte[] byteArray1, byte[] byteArray2) {
        byte[] result;
        BitSet bitSet = new BitSet(byteArray1.length * 8);
        
        for(int i = 0; i < byteArray1.length; i++) {
            int unsignedByte1 = Byte.toUnsignedInt(byteArray1[i]);
            int unsignedByte2 = Byte.toUnsignedInt(byteArray2[i]);
            for(int j = 0; j < 8; j++) {
                bitSet.set(i * 8 + j, unsignedByte1 % 2 != unsignedByte2 % 2);
                unsignedByte1 /= 2;
                unsignedByte2 /= 2;
            }
        }
        
        result = bitSet.toByteArray();
        return result;
    }

    private static byte substitueWithSbox(byte b) {
        int temp = Byte.toUnsignedInt(b);
        return (byte) SBOX[temp];
    }

    private static byte[] convertKeyToByteArray(String keyExample) {
        byte[] result = new byte[KEY_SIZE_IN_BYTE];
        
        for(int i = 0; i < keyExample.length(); i += 2) {
            result[i/2] = convertHexBlockToByte(keyExample.substring(i, i+2));
        }
        
        return result;
    }

    private static byte convertHexBlockToByte(String hexBlock) {
        return (byte) (convertHexDitgitToDecimal(hexBlock.charAt(0)) * HEX_BASE +
                            convertHexDitgitToDecimal(hexBlock.charAt(1)));
    }

    private static byte convertHexDitgitToDecimal(char hexDigit) {
        byte result = 0;
        
        switch(hexDigit) {
        case '0':
            result = 0;
            break;
        case '1':
            result = 1;
            break;
        case '2':
            result = 2;
            break;
        case '3':
            result = 3;
            break;
        case '4':
            result = 4;
            break;
        case '5':
            result = 5;
            break;
        case '6':
            result = 6;
            break;
        case '7':
            result = 7;
            break;
        case '8':
            result = 8;
            break;
        case '9':
            result = 9;
            break;
        case 'A':
            result = 10;
            break;
        case 'B':
            result = 11;
            break;
        case 'C':
            result = 12;
            break;
        case 'D':
            result = 13;
            break;
        case 'E':
            result = 14;
            break;
        case 'F':
            result = 15;
            break;
        }
        
        return result;
    }

}

Java ArrayIndexOutOfboundsException

你写的是不可能的。如果你按原样接受该代码，并且它有效，然后取消注释你标记的那一行并且不做其他任何更改，那么它就不可能崩溃：所有涉及的变量都是局部的，并且你写在紧接前一行。检查你的工作：这真的是你的代码吗，那里真的发生了异常吗？然后更新问题。temp[j]

0赞 MarsAtomic 7/18/2021

启动调试器并设置断点。逐步完成你的代码，确保你认为正在发生的事情实际上是正在发生的事情。提示：你可能弄错了。

答：

1赞 tgdavies 7/18/2021 #1

运行这个小程序，但首先尝试预测它将打印什么。然后考虑您的功能：xorWord

public class BitSetEg {
    public static void main(String... args) {
        BitSet b = new BitSet(32);

        byte[] bytes = b.toByteArray();
        System.out.println(bytes.length);
    }
}

未越界时得到 ArrayIndexOutOfBoundException

Got ArrayIndexOutOfBoundException when not out of bound

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