sha1
(PHP 4 >= 4.3.0, PHP 5, PHP 7, PHP 8)
sha1 — 文字列の sha1 ハッシュを計算する
警告
パスワードを守るためにこの関数を使うことはおすすめしません。 ハッシュアルゴリズムの高速性がその理由です。 詳細とベストプラクティスについては、パスワードハッシュ FAQを参照ください。
説明
» US Secure Hash Algorithm 1
を使用して string の sha1 ハッシュを計算します。
パラメータ
string-
入力文字列。
binary-
オプションの
binaryにtrueが指定された場合、sha1 ダイジェストは 20 バイト長のバイナリ形式で返されます。 それ以外の場合は、戻り値は 40 文字の 16 進数となります。
戻り値
sha1 ハッシュを文字列で返します。
例
例1 sha1() の例
<?php
$str = 'apple';
if (sha1($str) === 'd0be2dc421be4fcd0172e5afceea3970e2f3d940') {
echo "Would you like a green or red apple?";
}
?>
＋add a note
User Contributed Notes 31 notes
nathan ¶
16 years ago
The suggestion below to double-hash your password is not a good idea. You are much much better off adding a variable salt to passwords before hashing (such as the username or other field that is dissimilar for every account).
Double hashing is *worse* security than a regular hash. What you're actually doing is taking some input $passwd, converting it to a string of exactly 32 characters containing only the characters [0-9][A-F], and then hashing *that*. You have just *greatly* increased the odds of a hash collision (ie. the odds that I can guess a phrase that will hash to the same value as your password).
sha1(md5($pass)) makes even less sense, since you're feeding in 128-bits of information to generate a 256-bit hash, so 50% of the resulting data is redundant. You have not increased security at all.
Helpful Harry ¶
19 years ago
check out these randomized sha1 password storage functions, they output a string of 50 characters, the first 40 characters being a sha1 output based on the last 10 characters - those being a random seed
to encode a password run pw_encode with the password, it'll return a different pseudo-random string every time - store this value.
to check a password run pw_check with the password attempt and the stored value, it'll return true on a match and false otherwise
these functions eliminate the pesky problem of dictionary matches being run on your password lists
<?php
function pw_encode($password)
{
for ($i = 1; $i <= 10; $i++)
$seed .= substr('0123456789abcdef', rand(0,15), 1);
return sha1($seed.$password.$seed).$seed;
}
function pw_check($password, $stored_value)
{
if (strlen($stored_value) != 50)
return FALSE;
$stored_seed = substr($stored_value,40,10);
if (sha1($stored_seed.$password.$stored_seed).$stored_seed == $stored_value)
return TRUE;
else
return FALSE;
}
?>
bobm at hp dot com ¶
21 years ago
To achieve raw binary format prior to PHP5, you can do this...
$raw = pack("H*", sha1($str));
Regards,
Bob Mader
marcin at marcinwolny dot net ¶
11 years ago
Keep in mind that MD5 is less secure than SHA1.
Older CPUs can calculate MD5 over twice as fast as SHA1. GPUs in parallel calculations can handle MD5 over 3 times as fast as SHA1!
Two Radeon 79xx-series GPUs can calculate a rainbow table for 6-character lowercase MD5 password in... roughly 6 seconds!
Source: http://www.codinghorror.com/blog/2012/04/speed-hashing.html
Andre D ¶
16 years ago
Here's a better version of the getDigestNotation() function I posted earlier. (The first version had a bug in the argument checking.)
<?php
function getDigestNotation($rawDigest, $bitsPerCharacter, $chars = NULL)
{
if ($chars === NULL || strlen($chars) < 2) {
$chars = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ-,';
}
if ($bitsPerCharacter < 1) {
// $bitsPerCharacter must be at least 1
$bitsPerCharacter = 1;
} elseif (strlen($chars) < pow(2, $bitsPerCharacter)) {
// Character length of $chars is too small for $bitsPerCharacter
// Set $bitsPerCharacter to greatest value allowed by length of $chars
$bitsPerCharacter = 1;
$minCharLength = 2;
while (strlen($chars) >= ($minCharLength *= 2)) {
$bitsPerCharacter++;
}
unset($minCharLength);
}
$bytes = unpack('C*', $rawDigest);
$byteCount = count($bytes);
$out = '';
$byte = array_shift($bytes);
$bitsRead = 0;
for ($i = 0; $i < $byteCount * 8 / $bitsPerCharacter; $i++) {
if ($bitsRead + $bitsPerCharacter > 8) {
// Not enough bits remain in this byte for the current character
// Get remaining bits and get next byte
$oldBits = $byte - ($byte >> 8 - $bitsRead << 8 - $bitsRead);
if (count($bytes) == 0) {
// Last bits; match final character and exit loop
$out .= $chars[$oldBits];
break;
}
$oldBitCount = 8 - $bitsRead;
$byte = array_shift($bytes);
$bitsRead = 0;
} else {
$oldBitCount = 0;
}
// Read only the needed bits from this byte
$bits = $byte >> 8 - ($bitsRead + ($bitsPerCharacter - $oldBitCount));
$bits = $bits - ($bits >> $bitsPerCharacter - $oldBitCount << $bitsPerCharacter - $oldBitCount);
$bitsRead += $bitsPerCharacter - $oldBitCount;
if ($oldBitCount > 0) {
// Bits come from seperate bytes, add $oldBits to $bits
$bits = ($oldBits << $bitsPerCharacter - $oldBitCount) | $bits;
}
$out .= $chars[$bits];
}
return $out;
}
?>
novum123 at ribbonbazaar dot com ¶
18 years ago
So far as the dictionary attacks are concerned, I thought up the following function:
<?php
function twistSTR($array){
$twisted="";
$array_strlen=array();
foreach ($array as $element){
$array_strlen[]=strlen($element);
}
for ($i=0; $i<max($array_strlen); $i++){
foreach ($array as $element){
if ($i<strlen($element)){
$twisted=$twisted.$element{$i};
}
}
}
return $twisted;
}
?>
The twistSTR function basically takes an array input of strings and alternates each character of each string among all the other strings. For example:
<?php
echo twistSTR(array("this","and","that"));//output: tathnhidast
?>
It can be applied in the following manner:
<?php
if ($un===$_POST["username"] && $pwd===sha1(twistSTR(array($salt,$_POST["password"])))){
?>
It's not amazingly difficult to reverse engineer the actual output, but then again, that's not the point. The point is that when a password is entered into one of those databases, they are going to enter for example "thisandthat", not "tathnhidast".
ranko84 at gmail dot com ¶
16 years ago
Small update..., well more like fix to the obscure function, replace
<?php
if ($keepLength != NULL)
{
if ($hSLength != 0)
{
$hPassHash = substr($hPassHash, $hLPosition, -$hRPosition);
}
}
?>
with
<?php
if ($keepLength != NULL)
{
if ($hSLength != 0)
{
if ($hRPosition == 0)
{
$hPassHash = substr($hPassHash, $hLPosition);
}
else
{
$hPassHash = substr($hPassHash, $hLPosition, -$hRPosition);
}
}
}
?>
I've been getting few requests to explain how it's used so, this might be little long.
Problems:
1. In most solutions with hash and salt, you were bound to have one extra row in your database that would state, preferably random, salt for that hashed data. If attacker would manage to get drop of your database he would get hashed data and salt that is used with plain data to make it obscure, and then cracking that hashed data would be same as if you didn't add any salt to it.
2. I stumbled upon some functions that would hash data, then input salt into random places in hash and store it in database, but they would still have to write down random parameter used to scramble salt so they could reuse it when validating data. Getting simple database drop wouldn't help much here, but if they would manage to get their hands on obscuring function too, they could easily see what is salt and what hash.
Solutions:
1. Why use extra row to store salt when you can input it in hash. I'm not sure how attackers determine what type of hash are they facing, but I guess it has connection to hash length. In that case, why make attackers job easier and store in database data_hash+salt where they could assume just by it's length it has salt in there.
Reason behind $keepLength. If it's set to 1, strlen of hashed data plus salt would be equal to strlen of hashed data leading attacker to believe there is no salt.
If you leave $keepLength on NULL, strlen of final result would be strlen(used_hash_algorithm)+$hSLength.
$minhPass is there to reserve enough place for string that has to be hashed, so someone using this function wouldn't accidentally delete it by setting too high salt length ($hSLength), for example... if you set it 30000 it will keep working normal.
2. If you think about it, constant, but variable value when making input would be same data that is being input.
In case we're trying to hash password, and have user A with password "notme", password strlen equals to 5, and if we use default parameters of the function, with $keepLength set to 1, process would be:
random salt, hash it, add first 5 characters of hashed_salt at beginning of plain password, add last 5 characters of hashed_salt at end of plain password, hash it. Replace first 5 characters of hashed_password with first 5 character of hashed_salt, do same with last 5 characters of hashed_password, return hashed_password.
In case that string is longer than 10 characters function would use simple mathematics to reduce it to numbers lower than 10, well... lower than number that is stated in $hSLength.
And good thing is that every time user enters correct password it has same length so it's not necessary to write it anywhere.
So what is achieved in the end?
1. Attacker might not know that hash is salted, and you don't have that extra row in your database stating THIS IS SALT FOR THIS HASH.
2. If he does find out that it is, he wouldn't know what is hashed password and what is salt.
3. If he manages to get access to obscure function, only thing that might help him is value of $hSLength, where if $hSLength is set to 10 he would have to crack 10 variations of hashed string since he doesn't know how long password of user he's trying to crack is.
For example first variation would be hashed_password without last 10 characters, second variation would be hashed_password without first character and last 9 characters...
4. Even in case he has enough power to crack all 10 variations, resulting string that he might get doesn't necessarily has to be exactly long as password of original user in which case, attacker fails again.
mark at dot BANSPAM dot pronexus dot nl ¶
20 years ago
Looking for a simple function to implement HMAC-SHA1 but don't want to use the entire PEAR Message lib?
//Calculate HMAC-SHA1 according to RFC2104
// http://www.ietf.org/rfc/rfc2104.txt
function hmacsha1($key,$data) {
$blocksize=64;
$hashfunc='sha1';
if (strlen($key)>$blocksize)
$key=pack('H*', $hashfunc($key));
$key=str_pad($key,$blocksize,chr(0x00));
$ipad=str_repeat(chr(0x36),$blocksize);
$opad=str_repeat(chr(0x5c),$blocksize);
$hmac = pack(
'H*',$hashfunc(
($key^$opad).pack(
'H*',$hashfunc(
($key^$ipad).$data
)
)
)
);
return bin2hex($hmac);
}
It is very useful for client-authentication. see also http://cookies.lcs.mit.edu/pubs/webauth:tr.pdf
Optionally you can change $hashfunc to 'md5' to make this an HMAC-MD5 function ;-)
If you want raw or base64 output instead of hexadecimal, just change the last return line.
Cheers,
Mark
p.s. the "$hmac =" line used to be 1 line but I had to cut it up in order to fit it here ;)
Dan ¶
19 years ago
I've noticed websites are now starting to require passwords of a certain length that MUST contain at least 1 non-alphanumeric character. This in itself makes dictionary attacks kind of useless. My web site requires that as well. It uses md5, and appends a site code into the md5 as well. And the include file that contains that site key is outside the public folders. I sure hope I've done enough to keep the bad boys out.
Gregory Boshoff ¶
18 years ago
Note that the sha1 algorithm has been compromised and is no longer being used by government agencies.
As of PHP 5.1.2 a new set of hashing functions are available.
http://www.php.net/manual/en/function.hash.php
The new function hash() supports a new range of hashing methods.
echo hash('sha256', 'The quick brown fox jumped over the lazy dog.');
It is recommended that developers start to future proof their applications by using the stronger sha-2, hashing methods such as sha256, sha384, sha512 or better.
As of PHP 5.1.2 hash_algos() returns an array of system specific or registered hashing algorithms methods that are available to PHP.
print_r(hash_algos());
Anonymous ¶
15 years ago
Another solution to the salted hash with salt included directly in the hash, while keeping the same length of the result. If you want to generate a hash, call the function without the second argument. If you want to check a password against a hash, use the hash as the second argument. In this case, the function returns the hash itself on success, or boolean false on failure. You can also specify a hash algorithm as the third argument (otherwise SHA-1 will be used).
<?php
function __hash($password, $obscured = NULL, $algorithm = "sha1")
{
// whether to use user specified algorithm
$mode = in_array($algorithm, hash_algos());
// generate random salt
$salt = uniqid(mt_rand(), true);
// hash it
$salt = $mode ? hash($algorithm, $salt) : sha1($salt);
// get the length
$slen = strlen($salt);
// compute the actual length of salt we will use
// 1/8 to 1/4 of the hash, with shorter passwords producing longer salts
$slen = max($slen >> 3, ($slen >> 2) - strlen($password));
// if we are checking password against a hash, harvest the actual salt from it, otherwise just cut the salt we already have to the proper size
$salt = $obscured ? __harvest($obscured, $slen, $password) : substr($salt, 0, $slen);
// hash the password - this is maybe unnecessary
$hash = $mode ? hash($algorithm, $password) : sha1($password);
// place the salt in it
$hash = __scramble($hash, $salt, $password);
// and hash it again
$hash = $mode ? hash($algorithm, $hash) : sha1($hash);
// cut the result so we can add salt and maintain the same length
$hash = substr($hash, $slen);
// ... do that
$hash = __scramble($hash, $salt, $password);
// and return the result
return $obscured && $obscured !== $hash ? false : $hash;
}
?>
It uses a random, variable length salt, depending on the length of the password. The functions __scramble() and __harvest() are used to place salt into the hash or pull it out respectively. You can write your own, and of course the strength of the result greatly depends on them. They can be relatively simple yet still quite secure:
<?php
function __scramble($hash, $salt, $password)
{
return substr($hash, 0, strlen($password)) . $salt . substr($hash, strlen($password));
}
function __harvest($obscured, $slen, $password)
{
return substr($obscured, min(strlen($password), strlen($obscured) - $slen), $slen);
}
?>
Or they can be ridiculously complicated (my favourite kind):
<?php
function __scramble($hash, $salt, $password)
{
$k = strlen($password); $j = $k = $k > 0 ? $k : 1; $p = 0; $index = array(); $out = ""; $m = 0;
for ($i = 0; $i < strlen($salt); $i++)
{
$c = substr($password, $p, 1);
$j = pow($j + ($c !== false ? ord($c) : 0), 2) % (strlen($hash) + strlen($salt));
while (array_key_exists($j, $index))
$j = ++$j % (strlen($hash) + strlen($salt));
$index[$j] = $i;
$p = ++$p % $k;
}
for ($i = 0; $i < strlen($hash) + strlen($salt); $i++)
$out .= array_key_exists($i, $index) ? $salt[$index[$i]] : $hash[$m++];
return $out;
}
function __harvest($obscured, $slen, $password)
{
$k = strlen($password); $j = $k = $k > 0 ? $k : 1; $p = 0; $index = array(); $out = "";
for ($i = 0; $i < $slen; $i++)
{
$c = substr($password, $p, 1);
$j = pow($j + ($c !== false ? ord($c) : 0), 2) % strlen($obscured);
while (in_array($j, $index))
$j = ++$j % strlen($obscured);
$index[$i] = $j;
$p = ++$p % $k;
}
for ($i = 0; $i < $slen; $i++)
$out .= $obscured[$index[$i]];
return $out;
}
?>
sinatosk at gmail dot com ¶
20 years ago
Heres an SHA1 function that will work on it's own completely. This is for users who are using below PHP 4.3.0. it works same as PHP5 ( being able to return raw output ).
<?php
/*
** Date modified: 1st October 2004 20:09 GMT
*
** PHP implementation of the Secure Hash Algorithm ( SHA-1 )
*
** This code is available under the GNU Lesser General Public License:
** http://www.gnu.org/licenses/lgpl.txt
*
** Based on the PHP implementation by Marcus Campbell
** http://www.tecknik.net/sha-1/
*
** This is a slightly modified version by me Jerome Clarke ( sinatosk@gmail.com )
** because I feel more comfortable with this
*/
function sha1_str2blks_SHA1($str)
{
$strlen_str = strlen($str);
$nblk = (($strlen_str + 8) >> 6) + 1;
for ($i=0; $i < $nblk * 16; $i++) $blks[$i] = 0;
for ($i=0; $i < $strlen_str; $i++)
{
$blks[$i >> 2] |= ord(substr($str, $i, 1)) << (24 - ($i % 4) * 8);
}
$blks[$i >> 2] |= 0x80 << (24 - ($i % 4) * 8);
$blks[$nblk * 16 - 1] = $strlen_str * 8;
return $blks;
}
function sha1_safe_add($x, $y)
{
$lsw = ($x & 0xFFFF) + ($y & 0xFFFF);
$msw = ($x >> 16) + ($y >> 16) + ($lsw >> 16);
return ($msw << 16) | ($lsw & 0xFFFF);
}
function sha1_rol($num, $cnt)
{
return ($num << $cnt) | sha1_zeroFill($num, 32 - $cnt);
}
function sha1_zeroFill($a, $b)
{
$bin = decbin($a);
$strlen_bin = strlen($bin);
$bin = $strlen_bin < $b ? 0 : substr($bin, 0, $strlen_bin - $b);
for ($i=0; $i < $b; $i++) $bin = '0'.$bin;
return bindec($bin);
}
function sha1_ft($t, $b, $c, $d)
{
if ($t < 20) return ($b & $c) | ((~$b) & $d);
if ($t < 40) return $b ^ $c ^ $d;
if ($t < 60) return ($b & $c) | ($b & $d) | ($c & $d);
return $b ^ $c ^ $d;
}
function sha1_kt($t)
{
if ($t < 20) return 1518500249;
if ($t < 40) return 1859775393;
if ($t < 60) return -1894007588;
return -899497514;
}
function sha1($str, $raw_output=FALSE)
{
if ( $raw_output === TRUE ) return pack('H*', sha1($str, FALSE));
$x = sha1_str2blks_SHA1($str);
$a = 1732584193;
$b = -271733879;
$c = -1732584194;
$d = 271733878;
$e = -1009589776;
$x_count = count($x);
for ($i = 0; $i < $x_count; $i += 16)
{
$olda = $a;
$oldb = $b;
$oldc = $c;
$oldd = $d;
$olde = $e;
for ($j = 0; $j < 80; $j++)
{
$w[$j] = ($j < 16) ? $x[$i + $j] : sha1_rol($w[$j - 3] ^ $w[$j - 8] ^ $w[$j - 14] ^ $w[$j - 16], 1);
$t = sha1_safe_add(sha1_safe_add(sha1_rol($a, 5), sha1_ft($j, $b, $c, $d)), sha1_safe_add(sha1_safe_add($e, $w[$j]), sha1_kt($j)));
$e = $d;
$d = $c;
$c = sha1_rol($b, 30);
$b = $a;
$a = $t;
}
$a = sha1_safe_add($a, $olda);
$b = sha1_safe_add($b, $oldb);
$c = sha1_safe_add($c, $oldc);
$d = sha1_safe_add($d, $oldd);
$e = sha1_safe_add($e, $olde);
}
return sprintf('%08x%08x%08x%08x%08x', $a, $b, $c, $d, $e);
}
?>
rsemirag at yahoo dot com ¶
20 years ago
If you're struggling to generate an SHA encoded password for LDAP (PHP < 5.0), what you end up needing is this:
$userpassword = base64_encode(pack("H*", sha1($pass)));
I found this in the OpenLDAP FAQ (many thanks to Google and Ace), though I'm using the iPlanet LDAP server.
Ray Semiraglio
hkmaly ¶
7 years ago
Note: Before you get some idea like using sha1 with password as way to prevent others tampering with message, read pages "Length extension attack" and "Hash-based message authentication code" on wikipedia. In short, naive constructions can be dangerously insecure. Use hash_hmac if available or reimplement HMAC properly without shortcuts, like already shown in comment from mark at dot BANSPAM dot pronexus dot nl.
php at REMOVEMEkennel17 dot co dot uk ¶
19 years ago
It should be noted that sha1("") does not return an empty string. This means that if you are running a system that does not require users to have a password, the following code will not work as expected:
<?php
if ($StoredPassword == sha1($NewPassword))
// Password good
?>
If $StoredPassword and $NewPassword are both blank, then the password should be treated as good, but because sha1("") != "" it will be treated as bad. To get the correct behaviour you need to use:
<?php
if (($StoredPassword == "" && $NewPassword == "") || ($StoredPassword == sha1($NewPassword)))
// Password good
?>
(Note: I use a custom IsBlank() function instead of comparison against the empty string, so NULL values are also matched.)
For reference, here are a couple of special values put through sha1(). Note that sha1("") == sha1(NULL) == sha1(false), and also that sha1(0) != sha1(false)
"" -> da39a3ee5e6b4b0d3255bfef95601890afd80709
NULL -> da39a3ee5e6b4b0d3255bfef95601890afd80709
0 -> b6589fc6ab0dc82cf12099d1c2d40ab994e8410c
1 -> 356a192b7913b04c54574d18c28d46e6395428ab
false -> da39a3ee5e6b4b0d3255bfef95601890afd80709
true -> 356a192b7913b04c54574d18c28d46e6395428ab
WTM ¶
19 years ago
Actually, the post by Helpful Harry won't improve your security except for the most simple break in attempts. Since the random seed is attached to the end of the password hash, if you steal the hashed password, you steal the seed.
That means you can write a simple php program to call the pw_check function Harry included from a loop, feeding it dictionary words or random characters.
Of course, if you modified the program to use the seed in a more complicated way, "they" would have to know the new function's operation. But then again, if someone can steal your password database, they can probably steal your website code (or guess it).
mgcummings at yahoo dot com ¶
13 years ago
Thought I might save someone else some time trying to figure out how to generate a hash like MySQL5 PASSWORD() makes using just PHP.
$hash = '*' . sha1(sha1($pass), TRUE));
erling dot westenvik at gmail dot com ¶
18 years ago
Regarding php at REMOVEMEkennel17 dot co dot uk's note below:
The phrase: "To get the correct behaviour", would perhaps be better off if it read: "To get the wanted (but not recommended) behaviour".
Always honor the expected data types for functions: sha1 expects a string as input, and returns a string on exit. NULL, TRUE and FALSE are not string data types. The string "" is a string as good as "any". By following the "logic" that sha1("") should return "", then what should sha1("a") return? "b"? "c"?
An authentication system that allows for blank passwords is not really an authentication system in the first place. What you are describing is merely a way to tell the application that you want to see data in some specific context, like sorted by user name, etc. Create other tools for this purpose and leave the authentication system to deal with what it is supposed to do: Granting users access to restricted data and blocking other users from seeing the same data.
Don't store passwords in clear text, but salt and encrypt them. That way it makes perfect sense having <?php $sStoredPwd === sha1($sStoredSalt . $_POST["sTypedPwd"]); ?>, even with a blank "password". No other person than the user itself, not even the programmer, should know the password or be able to guess it. If the user forgets the password, a new one must be generated.
Regards,
Erling
Andr D ¶
16 years ago
Sometimes you want the digest in both readable notation (such as hexadecimal) and raw binary. At other times you want the digest in a notation other than hexadecimal.
The following getDigestNotation() function takes a binary string and returns it in base 2, 4, 8, 16, 32, or 64 notation. It works with sha1(), md5(), hash(), or anything else that can output a raw binary string.
It works similar to the session.hash_bits_per_character php.ini configuration option.
You can specify which characters to use for each position, or use the default, which matches session.hash_bits_per_character (0-9, a-z, A-Z, "-", ","). The practical range of bits to use per character ($bitsPerCharacter) is 1 to 6; you may use more, but you will have to provide your own base character string ($chars) that is at least pow(2, $bitsPerCharacter) characters long. So even with 7 bits per character you need to specify a value for $chars that is 128 characters long, which exceeds the number of printable ASCII characters.
The output's radix relates to the value of $bitsPerCharacter as follows:
1: base-2 (binary)
2: base-4
3: base-8 (octal)
4: base-16 (hexadecimal)
5: base-32
6: base-64
<?php
$raw = sha1(uniqid(mt_rand(), TRUE), TRUE);
echo getDigestNotation($raw, 6);
function getDigestNotation($rawDigest, $bitsPerCharacter, $chars = NULL)
{
if ($chars === NULL || strlen($chars) < 2) {
$chars '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ-,';
}
if ($bitsPerCharacter < 1) {
// $bitsPerCharacter must be at least 1
$bitsPerCharacter = 1;
} elseif (strlen($chars) < pow(2, $bitsPerCharacter)) {
// Character length of $chars is too small for $bitsPerCharacter
// Set $bitsPerCharacter to greatest value allowed by length of $chars
$bitsPerCharacter = 1;
do {
$bitsPerCharacter++;
} while (strlen($chars) > pow(2, $bitsPerCharacter));
}
$bytes = unpack('C*', $rawDigest);
$byteCount = count($bytes);
$out = '';
$byte = array_shift($bytes);
$bitsRead = 0;
for ($i = 0; $i < $byteCount * 8 / $bitsPerCharacter; $i++) {
if ($bitsRead + $bitsPerCharacter > 8) {
// Not enough bits remain in this byte for the current character
// Get remaining bits and get next byte
$oldBits = $byte - ($byte >> 8 - $bitsRead << 8 - $bitsRead);
if (count($bytes) == 0) {
// Last bits; match final character and exit loop
$out .= $chars[$oldBits];
break;
}
$oldBitCount = 8 - $bitsRead;
$byte = array_shift($bytes);
$bitsRead = 0;
} else {
$oldBitCount = 0;
}
// Read only the needed bits from this byte
$bits = $byte >> 8 - ($bitsRead + ($bitsPerCharacter - $oldBitCount));
$bits = $bits - ($bits >> $bitsPerCharacter - $oldBitCount << $bitsPerCharacter - $oldBitCount);
$bitsRead += $bitsPerCharacter - $oldBitCount;
if ($oldBitCount > 0) {
// Bits come from seperate bytes, add $oldBits to $bits
$bits = ($oldBits << $bitsPerCharacter - $oldBitCount) | $bits;
}
$out .= $chars[$bits];
}
return $out;
}
?>
Lastly, depending on the digest length, there may be fewer bits remaining for the last character than $bitsPerCharacter, so the last character will be smaller. The same thing happens with PHP's session ID generator, when 5 or 6 is used for session.hash_bits_per_character.