根据散列确认文件内容 [英] Confirming file content against hash

问题描述

我有要求检查文件的内容的完整性。这些文件将写入CD / DVD，可能会被复制多次。这个想法是识别正确复制的拷贝（在它们从Nero等被移除之后）。

对此很新颖，但快速搜索表明 Arrays.hashCode（byte []） 将符合需要。我们可以在磁盘上包含一个包含每个感兴趣资源的调用结果的文件，然后将它与的 byte [] 进行比较。文件在检查时从磁盘读取。

我是否正确理解该方法，这是检查文件内容的有效方法吗？ / p>

如果不是，则可以提供有关搜索关键字或策略/方法/类的建议。

---

基于Brendan答案的工作代码。它处理了VoidStar识别的问题（需要在内存中保存整个字节[] 以获取散列）。

  import java.io.File; 
 import java.io.FileInputStream; 
 import java.util.zip.CRC32; 
 $ b $ class TestHash {
 
 public static void main（String [] args）throws Exception {
 File f = new File（TestHash.java）; 
 FileInputStream fis = new FileInputStream（f）; 
 CRC32 crcMaker =新的CRC32（）; 
 byte [] buffer = new byte [65536]; 
 int bytesRead; （（bytesRead = fis.read（buffer））！= -1）{
 crcMaker.update（buffer，0，bytesRead）; 
} 
 long crc = crcMaker.getValue（）; //这是你的错误检查代码
 System.out.println（CRC代码是+ crc）; 
} 
} 
  

解决方案

Arrays.hashCode（）被设计为非常快（在散列表中使用）。我强烈建议不要将它用于此目的。

您需要的是某种错误检查代码，如 CRC 。

Java正好有一个类来计算这些： CRC32 ：

  InputStream in = ...; 
 CRC32 crcMaker =新的CRC32（）; 
 byte [] buffer = new byte [someSize]; 
 int bytesRead; （（bytesRead = in.read（buffer））！= -1）{
 crcMaker.update（buffer，0，bytesRead）; 
} 
 long crc = crcMaker.getValue（）; //这是你的错误检查代码
  

I have a requirement to 'check the integrity' of the content of files. The files will be written to CD/DVD, which might be copied many times. The idea is to identify copies (after they are removed from Nero etc.) which copied correctly.

Am rather new to this, but a quick search suggests that Arrays.hashCode(byte[]) will fit the need. We can include a file on the disk that contains the result of that call for each resource of interest, then compare it to the byte[] of the File as read from disk when checked.

Do I understand the method correctly, is this a valid way to go about checking file content?

If not, suggestions as to search keywords or strategies/methods/classes would be appreciated.

---

Working code based on the answer of Brendan. It takes care of the problem identified by VoidStar (needing to hold the entire byte[] in memory for getting the hash).

import java.io.File;
import java.io.FileInputStream;
import java.util.zip.CRC32;

class TestHash {

    public static void main(String[] args) throws Exception {
        File f = new File("TestHash.java");
        FileInputStream fis = new FileInputStream(f);
        CRC32 crcMaker = new CRC32();
        byte[] buffer = new byte[65536];
        int bytesRead;
        while((bytesRead = fis.read(buffer)) != -1) {
            crcMaker.update(buffer, 0, bytesRead);
        }
        long crc = crcMaker.getValue(); // This is your error checking code
        System.out.println("CRC code is " + crc);
    }
}

解决方案

Arrays.hashCode() is designed to be very fast (used in hash tables). I highly recommend not using it for this purpose.

What you want is some sort of error-checking code like a CRC.

Java happens to have a class for calculating these: CRC32:

InputStream in = ...;
CRC32 crcMaker = new CRC32();
byte[] buffer = new byte[someSize];
int bytesRead;
while((bytesRead = in.read(buffer)) != -1) {
    crcMaker.update(buffer, 0, bytesRead);
}
long crc = crcMaker.getValue(); // This is your error checking code

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