A simple example on incremental file hashing:
$fp = fopen($file, "r");
$ctx = hash_init('sha256');
while (!feof($fp)) {
$buffer = fgets($fp, 65536);
hash_update($ctx, $buffer);
}
$hash = hash_final($ctx, true);
fclose($fp);
While incremental hashing is quite slow, it's the easiest way to hash
- parts of large files: I.e., a 700MB avi video uses first x bytes to store metadata, so in order to hash the avi's data only, you have to fseek to data start and use incremental hashing
- streaming data if php just proxies the data
- whenever it's inadequate or impossible to store the data being hashed into memory (i.e. because of their size) or on disc.hash_update
(PHP 5 >= 5.1.2, PHP 7, PHP 8, PECL hash >= 1.1)
hash_update — Pump data into an active hashing context
Description
Parameters
context-
Hashing context returned by hash_init().
data-
Message to be included in the hash digest.
Return Values
Always returns true.
Changelog
| Version | Description |
|---|---|
| 8.4.0 | Now has a return type of true instead of bool. |
| 7.2.0 | Accept HashContext instead of resource. |
See Also
- hash_init() - Initialize an incremental hashing context
- hash_update_file() - Pump data into an active hashing context from a file
- hash_update_stream() - Pump data into an active hashing context from an open stream
- hash_final() - Finalize an incremental hash and return resulting digest
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User Contributed Notes 1 note
Dainichi ¶
19 years ago
