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hash_final combines file_put_contents to achieve data integrity verification

gitbox 2025-05-19

File data integrity verification usually refers to verifying whether a file has been tampered with or damaged during transmission or storage. To ensure file integrity, a hash algorithm is usually used. The hash algorithm converts the contents of a file into a fixed-length string called a "hash" or "summary". If the file content changes, its corresponding hash value will also change.

2. Introduction to hash_final function

In PHP, the hash_final function is used to return the final result of the hash context. This function is usually used in conjunction with hash_init and hash_update to handle hash calculations of file or string data. The basic syntax is as follows:

 string hash_final ( resource $context [, bool $raw_output = false ] )

  • $context is a hash context resource returned by hash_init .

  • $raw_output is an optional parameter, default to false , which means that the hash value returned in hexadecimal format. If set to true , the original binary hash value is returned.

3. Introduction to file_put_contents function

file_put_contents is a file operation function in PHP that writes data to a file. Its basic syntax is as follows:

 int file_put_contents ( string $filename , mixed $data [, int $flags = 0 [, resource $context ]] )

  • $filename is the file name to be written.

  • $data is the data to be written.

  • $flags is an optional parameter that indicates the behavior during writing, such as whether to overwrite the file or append data.

  • $context is an optional parameter that represents the context of the file operation.

4. Realize file data integrity verification

Combining hash_final and file_put_contents functions, we can implement a simple file integrity verification mechanism. Here are the detailed steps of the implementation process:

  1. Initialize hash calculation : First, we use the hash_init function to initialize a hash context, specifying the hash algorithm used (for example, sha256 ).

  2. Read file content and update hash : Use the hash_update function to read the contents of the file and update the hash value every time it is read.

  3. Write to file : Write file contents to the specified file through the file_put_contents function.

  4. Generate hash value of the file : Finally, the final hash value is obtained through the hash_final function and saved as part of the file or stored in the database.

5. Sample code

Here is a sample code to implement file data integrity verification using hash_final and file_put_contents functions:

 <?php
// File path
$filePath = 'path/to/your/file.txt';

// Initialize hash context
$context = hash_init('sha256');

// Read file content and update hash value
$fileContent = file_get_contents($filePath);
hash_update($context, $fileContent);

// Get the final hash value
$hashValue = hash_final($context);

// Write file contents to the target file
$targetFilePath = 'path/to/your/destination/file.txt';
file_put_contents($targetFilePath, $fileContent);

// Save hash values ​​to a file or database（For subsequent verification）
$hashFilePath = 'path/to/your/file_hash.txt';
file_put_contents($hashFilePath, $hashValue);

// Output hash value
echo "The hash value of the file is: " . $hashValue;
?>

6. Verify file integrity

Once the file content and corresponding hash value have been saved, we can verify the integrity of the file through the following steps:

  1. Read file content : First, read the content of the target file.

  2. Calculate the hash value of the file : Then, use the same hash algorithm to calculate the hash value of the file.

  3. Compare hash : Finally, compare the calculated hash value with the saved hash value. If the two are consistent, it means that the file has not been tampered with; if it is inconsistent, it means that the content of the file has changed.

Here is a code example for verifying file integrity:

 <?php
// Read the saved hash value
$storedHash = file_get_contents('path/to/your/file_hash.txt');

// Read the content of the target file
$fileContent = file_get_contents('path/to/your/destination/file.txt');

// Initialize hash context并计算文件哈希值
$context = hash_init('sha256');
hash_update($context, $fileContent);
$calculatedHash = hash_final($context);

// Compare hash values
if ($storedHash === $calculatedHash) {
    echo "File integrity verification passed，The file has not been tampered with。";
} else {
    echo "File integrity verification failed，The file may have been tampered with。";
}
?>

7. Summary

By combining PHP's hash_final and file_put_contents functions, we can implement a simple file data integrity verification mechanism. In actual development, we can use this method to ensure that the data of the file during storage or transmission is not tampered with. To improve security, it is recommended to choose a hashing algorithm with higher security, such as sha256 or sha512 , and combine other security measures to protect the integrity of file data.

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