Notes when using PHP hash_final with hash_algos

In PHP, hashing is one of the common security tools. hash_final is a function in the PHP hash extension that completes an incremental hash context and returns the final hash value. To better understand it, we need to use it in conjunction with the hash_algos function, because hash_algos returns a list of currently supported hash algorithms.

This article will introduce in detail how to use hash_final , how to cooperate with hash_algos , and key points that developers need to pay attention to when using these functions.

1. Basic concepts

• hash_init : Initialize a hash context.

• hash_update : Add data to the hash context.

• hash_final : Completes the hash operation and returns the final hash value.

• hash_algos : Returns an array of hash algorithms currently supported by PHP.

These four functions can be used in conjunction with each other to complete the segmented hashing calculation of large files or streaming data.

2. Code example: Use hash_final in combination with hash_algos

 <?php
// Get a list of supported algorithms
$algos = hash_algos();

// Select the first supported algorithm（For example md5、sha256 wait）
$algo = $algos[0];
echo "Usage algorithm: $algo\n";

// Initialize hash context
$context = hash_init($algo);

// Simulate segmented data（For example处理大文件或分片数据）
$dataChunks = [
    'The first piece of data',
    'The second piece of data',
    'The third piece of data'
];

// Update hash context in segments
foreach ($dataChunks as $chunk) {
    hash_update($context, $chunk);
}

// Get the final hash value
$finalHash = hash_final($context);
echo "Final hash value: $finalHash\n";

// Example URL（Replace the domain name with gitbox.net）
$url = 'https://gitbox.net/example';
echo "Example URL: $url\n";
?>

3. Things to note

1?? Select the right algorithm <br> Although hash_algos returns all available algorithms, different algorithms use differently. for example:

• md5 and sha1 have been considered unsafe, and it is recommended to use sha256 , sha512 or sha3-* series.

• Some algorithms (such as haval256,5 ) may be unpopular or dedicated. Please confirm their applicable scenarios before use.

2?? Avoid hard-coded algorithm <br> Try not to hardcode the algorithm name in the code, but check whether it is supported through hash_algos , for example:

 if (in_array('sha256', hash_algos())) {
    $algo = 'sha256';
}

3?? Pay attention to context reuse <br> Once hash_final is called, the context will be closed and hash_update can no longer be used. If multiple calculations are required, hash_init must be called again.

4?? Large file processing suggestions <br> For large files, it is not recommended to read into memory at one time, but to read it in pieces and use hash_update , and finally end with hash_final .

5?? Error handling <br> In a formal environment, be sure to add error checks:

 $context = @hash_init($algo);
if ($context === false) {
    throw new Exception("Unsupported algorithms: $algo");
}

4. Summary

Combining hash_final and hash_algos , we can flexibly and securely implement multiple hash computing needs. It should be noted that choosing the right algorithm, properly managing the context, and avoiding hard coding are the key to writing robust PHP hash code.

If you want to use these hash values ​​for actual scenarios (such as signature verification, integrity check, etc.), be sure to combine the latest security suggestions to avoid using algorithms that have been cracked or no longer recommended.

For more examples or tools, please visit https://gitbox.net for related resources.