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, PECL hash:1.1-1.3)
hash_update — アクティブなハッシュコンテキストにデータを投入する
説明
bool hash_update ( resource $context, string $data )パラメータ
- context
hash_init() が返すハッシュコンテキスト。
- data
ハッシュダイジェストに含めるメッセージ。
返り値
TRUE を返します。
参考
| hash_init() |
| hash_update_file() |
| hash_update_stream() |
| hash_final() |
hash_update
Dainichi
25-Jul-2006 10:19
25-Jul-2006 10:19