Please take note that hash-file will throw error on files >=2GB.
(PHP 5 >= 5.1.2, PECL hash >= 1.1)
hash_file — Generate a hash value using the contents of a given file
$raw_output= false ] )
Name of selected hashing algorithm (i.e. "md5", "sha256", "haval160,4", etc..)
URL describing location of file to be hashed; Supports fopen wrappers.
When set to
TRUE, outputs raw binary data.
FALSE outputs lowercase hexits.
Returns a string containing the calculated message digest as lowercase hexits
raw_output is set to true in which case the raw
binary representation of the message digest is returned.
Example #1 Using hash_file()
/* Create a file to calculate hash of */
file_put_contents('example.txt', 'The quick brown fox jumped over the lazy dog.');
echo hash_file('md5', 'example.txt');
The above example will output:
If you want to use hash_file() to get the CRC32 value of a file, use the following to unpack the hex string returned by the function to an integer (similar to crc32()):
$hash = hash_file('crc32b', $filepath);
$array = unpack('N', pack('H*', $hash));
$crc32 = $array;
The 'octets reversed' you are seeing is the bug 45028 which has been fixed. http://bugs.php.net/bug.php?id=45028
The difference between crc32 and crc32b is explained on mhash man page. crc32 is the one used on ethernet, while crc32b is the one used on zip, png... They differ on the table used.
The Hash_File() function returns the same value as if the function Hash() had been performed on the same exact piece of data. At first, I was uncertain if Hash_File() used the filename, or even the permission settings, when defining the data to be hashed for the given algorithm. If it did work that way, then that means the same exact files would have different HASH values when you moved or renamed them on your system. Anyway, fortunately, it does not work that way. Hash() and Hash_File() produce identical results for the same pieces of data. This is also true for the relationship between the Hash_HMAC() and Hash_HMAC_File() functions: the same pieces of data, the same keys, produce identical results. It was a wise, design principle.
Some sample code to demonstrate this principle :
// Author: firstname.lastname@example.org
// Preset Data
$test_data = "php-hashing";
$test_file = "test.txt";
$test_file_read = file_get_contents($test_file);
// Hash Data
$test_data_hash = hash("md2", $test_data, FALSE);
$test_file_hash = hash_file("md2", $test_file, FALSE);
// Print Hash Results
print("Data Hash ($test_data): $test_data_hash<br><br>");
print("File Hash ($test_file_read): $test_file_hash");
Data Hash (php-hashing): 457d84e1d69e519a7b73348db21477d3
File Hash (php-hashing): 457d84e1d69e519a7b73348db21477d3
I have verified that the output of the "crc32" is the ITU I.363.5 algorithm (a.k.a. AAL5 CRC - popularised by BZIP2 but also used in ATM transmissions - the algorithm is the same as that in POSIX 1003.2-1992 in Cksum but that stuffs the size into the CRC at the end for extra measure). However, the output is expressed in reverse order to many CRC programs. Using the "standard" crctest.txt (numbers 1 to 9 in sequence - google it, it's not hard to find), php will output 181989fc - many other (Intel little endian) programs would output this as fc891918, hence the confusion (that I have had, at least).
The crc32b is the 32-bit Frame Check Sequence of ITU V.42 (used in Ethernet and popularised by PKZip). The output from this CRC is popularised in Intel little endian format and would produce cbf43926 on the same file.
For those who are wondering, there appears to be no fundamental difference between hash_file('md5')/hash_file('sha1') and md5_file()/sha1_file(). They produce identical output and have comparable performance.
There is, however, a difference between hash_file('crc32') and something silly like crc32(file_get_contents()).
crc32(file_get_contents())'s results are most similar to those of hash_file('crc32b'), just with the octets reversed:
$fname = "something.png";
$hash = hash_file( 'crc32', $fname );
echo "crc32 = $hash\n";
$hash = hash_file( 'crc32b', $fname );
echo "crc32b = $hash\n";
$hash = sprintf("%x",crc32(file_get_contents($fname)));
echo "manual = $hash\n";
crc32 = f41d7f4e
crc32b = 7dafbba4
manual = a4bbaf7d