AES加密/解密java充氣城堡解釋？

Question

有人可以解釋一下這個程序在做什麼，指出一些主要觀點？我在看代碼，我完全迷失了。我只需要解釋加密/解密階段。我認爲它在一個點上生成了AES 192密鑰，但我不是100％確定的。我不確定byte/ivBytes用於哪一個。

import java.security.Key; 
import javax.crypto.Cipher; 
import javax.crypto.KeyGenerator; 
import javax.crypto.spec.IvParameterSpec; 

public class RandomKey 
{ 
    public static void main(String[] args) throws Exception 
    { 
    byte[] input = new byte[] { 
         0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 
         0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f, 
         0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07 }; 


    byte[] ivBytes = new byte[] { 
         0x00, 0x00, 0x00, 0x01, 0x04, 0x05, 0x06, 0x07, 
         0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01 }; 

    //initializing a new initialization vector 
    IvParameterSpec ivSpec = new IvParameterSpec(ivBytes); 
    //what does this actually do? 
    Cipher cipher = Cipher.getInstance("AES/CTR/NoPadding", "BC"); 
    //what does this do? 
    KeyGenerator generator = KeyGenerator.getInstance("AES","BC"); 
    //I assume this generates a key size of 192 bits 
    generator.init(192); 
    //does this generate a random key? 
    Key encryptKey = generator.generateKey(); 

    System.out.println("input: " +toHex(input)); 

    //encryption phase 
    cipher.init(Cipher.ENCRYPT_MODE, encryptKey, ivSpec); 
    //what is this doing? 
    byte[] cipherText = new byte[cipher.getOutputSize(input.length)]; 
    //what is this doing? 
    int ctLength = cipher.update(input, 0, input.length, cipherText,0); 

    //getting the cipher text length i assume? 
    ctLength += cipher.doFinal (cipherText, ctLength); 
    System.out.println ("Cipher: " +toHex(cipherText) + " bytes: " + ctLength); 


    //decryption phase 
    cipher.init(Cipher.DECRYPT_MODE, encryptKey, ivSpec); 
    //storing the ciphertext in plaintext i'm assuming? 
    byte[] plainText = new byte[cipher.getOutputSize(ctLength)]; 
    int ptLength = cipher.update(cipherText, 0, ctLength, plainText, 0); 
    //getting plaintextLength i think? 
    ptLength= cipher.doFinal (plainText, ptLength); 
    System.out.println("plain: " + toHex(plainText, ptLength)); 

    } 

private static String digits = "abcdef"; 

public static String toHex(byte[] data, int length) 
{ 
    StringBuffer buf = new StringBuffer(); 

    for (int i=0; i!= length; i++) 
    { 
     int v = data[i] & 0xff; 

     buf.append(digits.charAt(v >>4)); 
     buf.append(digits.charAt(v & 0xf)); 
    } 
    return buf.toString(); 

} 

public static String toHex(byte[] data) 
{ 
    return toHex(data, data.length); 
} 
} 

Answer 1

你試過在這裏？

http://docs.oracle.com/javase/6/docs/api/javax/crypto/Cipher.html

http://docs.oracle.com/javase/6/docs/api/javax/crypto/KeyGenerator.html

你的代碼是如何加密和Java中解密字節數據的非常簡單的代碼示例。

一旦你通讀了類文檔，你可以更好地表達你關於這段代碼行爲的問題。

Answer 2

//what does this actually do? 
Cipher cipher = Cipher.getInstance("AES/CTR/NoPadding", "BC"); 

這裏使用了充氣城堡（「BC」）提供不帶填充（NoPadding）來獲取AES暗號的一個實例，在計數器模式（CTR）成立。請參閱維基百科Block Cypher modes和Padding。 Javadoc也會幫助你。

//what does this do? 
KeyGenerator generator = KeyGenerator.getInstance("AES","BC"); 

這同樣採用了充氣城堡供應商建立了AES密鑰生成器。您可以閱讀Javadoc以瞭解更多信息。

//what is this doing? 
byte[] cipherText = new byte[cipher.getOutputSize(input.length)]; 

它建立了大到足以容納加密輸出的字節的陣列。

//what is this doing? 
int ctLength = cipher.update(input, 0, input.length, cipherText,0); 

它實際上是在加密。檢查Javadoc的update()方法是否有很好的解釋。

//getting the cipher text length i assume? 
ctLength += cipher.doFinal (cipherText, ctLength); 

號看那個+=它是更新密文長度。再次閱讀Javadoc的update()和doFinal()方法之間的區別。