Is there any PHP function that encodes a string to a int value, which later I can decode it back to a string without any key?
Sure, you can convert strings to numbers and vice versa. Consider:
$a = "" + 1
gettype($a) // integer
$b = "$a"
gettype($b) // string
You can also do type casting with settype().
If I misunderstood you and you want to encode arbitrary strings, consider using base64_encode() and bas64_decode(). If you want to convert the base 64 string representation to a base 10 integer, simply use base_convert().
And int has 4 or 8 bytes depending on the platform, and each character in a string is one byte (or more depending on encoding). So, you can only encode very small strings to integers, which basically makes the answer to your question: no.
What do you want to accomplish?
I would suspect not, since there are far more possible string combinations than integers within the MAX_INT.
Does it have to be an integer?
i'm convinced that what you think you want to do is not really what you want to do. :-) this just sounds like a silly idea. As another user has asked before:) what do you need this for? What are your intentions?
Well now that you mentioned that numbers and a-z letter are acceptable, then I have one suggestion, you could loop through the individual letters' ordinal value and display that as a two-digit hexadecimal. You can then convert these hexadecimals back to the ordinal values of the individual characters. Don't know what kind of characters are you about to encode, possibly you will need to use 4-characters per letter (e.g. String Peter would become 00700065007400650072 ) Well... have fun with that, I still don't really see the rationale for doing what you're doing.
op through the individual letters' ordinal value and display that as a two-digit hexadecimal. You can then convert these hexadecimals back to the ordinal values of the individual characters. Don't know what kind of characters are you about to encode, possibly you will need to use 4-characters per letter (e.g. String Peter would become 00700065007400650072 ) Well... have fun with that, I still don't really see the
There is no function for PHP but I recently wrote a class to encrypt and decrypt a string in PHP. You can look at it at: https://github.com/Lars-/PHP-Security-class
Related
If I've read a binary file into a variable using $data = fread('myfile','rb') how can I work through $data a byte at a time. I also want to perform operations on each byte, such as multiplying it by a number and calculating the modulo with respect to another number.
I can reference the variable as an array using $data[$i], but am I getting bytes with this or possibly multi-byte characters? Also when I do this, I can't then perform calculations on the results, such as $data[$i]*4, which is always zero.
I need work through very large files so the solution needs to be quick.
Thanks
I can reference the variable as an array using $data[$i], but am I getting bytes with this or possibly multi-byte characters?
You'll get bytes. PHP strings are single-byte.
Also when I do this, I can't then perform calculations on the results, such as $data[$i]*4, which is always zero.
Convert a character to a number with ord, make your calculations and, if needed, convert back with chr. Alternatively, convert the whole buffer with unpack('c*', $buf), which gives you a numeric array.
The PHP manual on String conversion to numbers says:
The value is given by the initial portion of the string. If the string starts with valid numeric data, this will be the value used. Otherwise, the value will be 0 (zero).
This means that anything other than a number, plus or minus at the beginning of a string should return 0 when the string is converted to a number. Yet, (some) whitespace at the beginning of a string is ignored:
echo intval(" 3"); // 3
echo intval("
3"); // 3
Is there any kind of whitespace that intval() and (int) do not strip?
Where is this behavior documented?
The observed behavior is largely undocumented. Probably the space stripping depends on strtod() in C, which should use isspace().
intval() manual says:
The common rules of integer casting apply.
Following the link (links removed):
To explicitly convert a value to integer, use either the (int) or (integer) casts. However, in most cases the cast is not needed, since a value will be automatically converted if an operator, function or control structure requires an integer argument. A value can also be converted to integer with the intval() function.
So it looks like casting and intval() are equivalent. And a little below the quote above:
From strings
See String conversion to numbers
OK. Nothing really helpful there for us, except this little note:
For more information on this conversion, see the Unix manual page for strtod(3).
Following the thread of links again, choosing the version of strtod() specified in POSIX, the API standard for UNIX.
These functions shall convert the initial portion of the string pointed to by nptr to double, float, and long double representation, respectively. First, they decompose the input string into three parts:
1. An initial, possibly empty, sequence of white-space characters (as specified by isspace())
…
Common sense tells us that this should apply to floats only because strtod() returns a floating point number in C, but number parsing and internal representation is quirky in PHP, as much as almost everything in this language. Who knows how it really works under the hood. Better not to know.
I have a large string $string that when applied to md5(), give me
c4ca4238a0b923820dcc509a6f75849b
The length is 32, I want to reduce it, so
base64_encode(md5($string, true));
xMpCOKC5I4INzFCab3WEmw==
Removing the last two == it give me a string with length = 22.
Are there any other better algorithms?
I am not sure you realised that md5 is a hash function, and therefore irreversible. If you do not care about reversibility, you could just as well trim the md5 hash (or any hash of your liking*) down to an arbitrary number of characters. All this would do is increase the likelihood of collision (I feel this does not produce an uniform distribution though).
If you are looking for a reversible (ie. non-destructive) compression, then do not reinvent the wheel. Use the built-in functions, such as gzdeflate() or gzcompress(), or other similar functions.
*Here is a list of hash functions (wikipedia) along with the size of their output.
I suppose the smallest possible "hash function" would be a parity bit :)
One better way would be to, instead of converting to binary to hexadecimal (as md5 does) and then converting the string to base64, instead convert from the hexadecimal md5 directly to base64.
Since hexadecimal is 16 bits per character, and base64 is 64 bits per character, every 2 hexadecimal characters will make up one base64 character.
To perform the conversion, you can do the following:
Split the string into sixteen 2 character chunks
The first character should be multiplied by 2 and added to the second (keeping in mind that A-F = 10-15).
This number can be matched to the base64 scheme using the table from here: https://en.wikipedia.org/wiki/Base64
This will result in a 16 character base64 string with the same value as the hexadecimal representation of the md5 string.
Theoretically, you could do the same for any base. If we had a way to encode base128 strings in ASCII, we could end up with an 8 character string. However, as the character set is limited, I think base64 is the highest base that is commonly used.
The smaller the length of the string you want .. the smaller the number of possible combination
Total Number of Possibility with reputation
Total Possibility = nr
Since we are dealing with base64 has the printable output this means we only have 64 characters
n = 64
If you are looking at 22 letters in length
nr = 6422 = 5,444,517,870,735,015,415,413,993,718,908,291,383,296 possibilities
Back to your question : Are there any better algorithm?
Truncate the string with a good hash to desired length you want since the total possibility and collision is fixed
$string = "the fox jumps over the lazy brown dog";
echo truncateHash($string, 8);
Output
9TWbFjOl
Function Used
function truncateHash($str, $length) {
$hash = hash("sha256", $str, true);
return substr(base64_encode($hash), 0, $length);
}
This encoding generates shorter string,
print base64_encode(hash("crc32b",$string,1));
output
qfQIdw==
Not sure if MD5 is the right choice for you, but i will assume that you have reason to stick with this algorithm and are looking for a shorter representation. There are several possibilities to generate a shorter string with different alphabets:
Option 1: Binary string
The shortest possbile form of an MD5 is it's binary representation, to get such a string you can simply call:
$binaryMd5 = md5($input, true);
This string you can store like any other string in a database, it needs only 16 characters. Just make sure you do a proper escaping, either with mysqli_real_escape_string() or with parametrized queries (PDO).
Option 2: Base64 encoding
Base64 encoding will produce a string with this alphabet: [0-9 A-Z a-z + /] and uses '=' as padding. This encoding is very fast, but includes the sometimes unwanted characters '+/='.
$base64Md5 = base64_encode(md5($input, true));
The output length will be always 24 characters for the MD5 hash.
Option 3: Base62 encoding
The base62 encoding only uses the alphabet [0-9 A-Z a-z]. Such strings can be safely used for any purpose like tokens in an URL, and they are very compact. I wrote a base62 encoder, which is able to convert binary strings to the base62 alphabet. It may not be the fastest possible implementation, but it was my goal to write understandable code. The same class could be easily adapted to different alphabets.
$base62Md5 = StoBase62Encoder::base62encode(md5($input, true));
The output length will vary from 16 to 22 characters for the MD5 hash.
Base 91 looks like the most space efficient binary to ASCII printable encoding algorithm (which is what it seems you want).
I've not seen the PHP implementation, but if your software has to work with others I'd stick to Base 64; it's well-known, lightning fast, and available everywhere.
Firstly, to answer your question: Yes, there is a better algorithm (if with "better" you mean "shorter").
Use the hash() function (which has been part of the PHP core and enabled by default since PHP 5.1.2.) with any of the adler32, fnv132, crc32, crc32b, fnv132 or joaat algorithms.
Without a more in-depth knowledge of your current situation, you might as well just pick whichever one you think sounds the coolest.
Here is an example:
hash('crc32b', $string)
I set up an online example you can play around with.
Secondly, I would like to point out that what you are asking is an almost exact duplicate of another question here on stackoverflow.
I read from your post that you are searching for a hashing algorithm and not compression.
There are various standard hashing algorithms in php out there. Have a look at PHP hashing functions.
Depending on what you want to hash there are different approches. Be careful and calculate the average collision probability.
However it seems you are searching for a 'compression' which outputs the minimum possible size of chars for a given string. If you do, then have a look at Lempel–Ziv–Welch (php implementation) or others.
I'm trying to use the API of a web service provider. They don't have an example in Ruby, but they do have one for PHP, and I'm trying to interpret between the two. The API examples always use "true" on PHP's hash_hmac() call, which produces a binary output. The difference seems to be that Ruby's OpenSSL::HMAC.hexdigest() function always returns text. (If I change the PHP call to "false" they return the same value.) Does anyone know of a way to "encode" the text returned from OpenSSL::HMAC.hexdigest() to get the same thing as returned from a hash_hmac('sha256', $text, $key, true)?
Use OpenSSL::HMAC.digest to get the binary output.
You'll need to convert each pair of hex digits into a byte with the same value. I don't know any Ruby, but this is similar to how it would be handled in PHP.
First, take your string of hex digits and split them into an array. Each element in the array should be two characters long. Convert each element from a string of two hex bytes to an integer. It looks like you can do this by calling the hex method on each string.
Next, call pack on the converted array using the parameter c*, to convert each integer into a one-byte character. You should get the correct string of bytes as the result.
Is there a native or inexpensive way to check for the length of a string in bytes in PHP?
See http://bytes.com/topic/php/answers/653733-binary-string-length
Relevant part:
"In PHP, like in C, the string ends with a zero-character, '\0', (char)
0, null-terminator, null-byte or whatever you like to call it."
No, that's not the case - PHP strings are stored with both the length and the
data, unlike C strings that just has one pointer and uses a terminator. They're
"binary-safe" - NUL doesn't terminate the string.
See the definition of zvalue_value in zend.h; the string part has both a "char
*val" and "int len".
Problems would start if you're using the mbstring.func_overload, which changes
how strlen() and the other functions work, and does try and treat strings as
strings of characters in a specific encoding rather than a string of bytes.
This is not the normal PHP behaviour.
The answer is that strlen should return the number of bytes regardless of the content of the string. For multi-byte character strings, you get the wrong number of characters, but the right number of bytes. However, you need to be certain you're not using the mbstring overload, which changes how strlen behaves.
In the event that you have mbstring overload set or your are developing for the platforms where you are unsure about this setting you can do the following:
$len=strlen(bin2hex($data))/2;
The reason why this works is that in Hex you are guaranteed to get 2 characters for all bytes that come from bin2hex (it returns two chars even for the initial binary 0).
Note that it will use significantly more resources than a normal strlen (afterall, so you should definitely not do that to the large amount of data if it's not absolutely necessary.
On php.org, someone was nice enough to create this function. Just multiply by 8 and you've got however many bits were in that string, as the function returns bytes.
The length of a string (textual data) is determined by the position of the NULL character which marks the end.
In case of binary data, NULL can be and often is in the middle of data.
You don't check the length of binary data. You have to know it beforehand. In your case, the length is 16 (bytes, not bits, if it is UUID).
As far as UUID validity is concerned, any 16-byte value is a valid UUID, so you are out of luck there.