Java - 加密部分文件（音頻和圖像）而不是整個文件？

Question

我看了一下這這裏 Android - Increase speed of encryption

我只需要加密的文件的一部分（音頻&圖像）。這可能嗎？如果可能的話，有人可以提供加密和解密片段嗎？

在此先感謝=）

Answer 1

你可以定義一個加密的成員，你的類的非加密的成員。然後，只是適當地序列化它們。例如，你的班級可能是這樣的：

public Class partiallyEncrypted { 
    private transient byte[] imagePart1Decrypted; // transient member will not be serialized by default 
    private byte[] imagePart1Encrypted; 
    private byte[] imagePart2; 
    private static final int BYTES_TO_ENCRYPT = 2048; 
    // other non-encrypted fields 
    ... 

    public setImage(byte[] imageBytes) { 
    // calc bytes to encrypt and those left over, initialize arrays 
    int bytesToEncrypt = Math.min(imageBytes.length, BYTES_TO_ENCRYPT); 
    int bytesLeftOver = Math.max(imageBytes.length - bytesToEncrypt, 0); 
    imagePart1Decrypted = new byte[bytesToEncrypt]; 
    imagePart2 = new byte[bytesLeftOver]; 

    // copy data into local arrays 
    System.arraycopy(imageBytes, 0, imagePart1Decrypted, 0, bytesToEncrypt); 
    if (bytesLeftOver > 0) 
     System.arraycopy(imageBytes, bytesToEncrypt, imagePart2, 0, bytesLeftOver); 

    imagePart1Encrypted = encrypt(bytesToEncrypt); 
    } 

    public byte[] getImage() { 
    if (imagePart1Decrypted == null) 
     imagePart1Decrypted = decrypt(imagePart1Encrypted); 

    byte[] fullImage = new byte[imagePart1Decrypted.length + imagePart2.length]; 
    System.arraycopy(imagePart1Decrypted, 0, fullImage, 0, imagePart1Decrypted.length); 
    if (imagePart2 != null && imagePart2.length > 0) 
     System.arraycopy(imagePart2, 0, fullImage, imagePart1Decrypted.length, imagePart2.length); 

    return fullImage; 
    } 
}