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Getting issue when convert c# code to PHP as below

I am running this code:
var timeStamp = DateTime.UtcNow;
var sharedSecret = "xx";
var saltedString = timeStamp.ToString("2021-01-07T16:42:33.619667Z") + sharedSecret;
//Encoding saltedString using Unicode little-endian byte order
byte[] encodedSaltedString = Encoding.Unicode.GetBytes(saltedString);
//Hashing Algorithm used is SHA512
HashAlgorithm hash = new SHA512Managed();
//Compute Hash of encodedSaltedString
byte[] hashedEncodedString = hash.ComputeHash(encodedSaltedString);
//Convert hashed array to base64-encoded string
string signature = Convert.ToBase64String(hashedEncodedString);
I am then getting this result in C#:
"gQhjrLnY6fo44EeaaWaUBE1PY/8oEIRsUcK3AMSCVUCYMM4vRfxvQEEggXaHTF0GQbw4w2HbWArX1k6NnkzJFg=="
I converted to this code as below, but I am getting an issue. Can I get some help on this?
$timestamp = "2021-01-07T16:42:33.619667Z";
$sharedSecret = 'xx';
$saltedString = $timestamp.$sharedSecret;
$utf=mb_convert_encoding($saltedString, "UTF-16LE");
$signature = base64_encode(hash('sha512', $utf));
IN PHP I am getting this result:
ODEwODYzYWNiOWQ4ZTlmYTM4ZTA0NzlhNjk2Njk0MDQ0ZDRmNjNmZjI4MTA4NDZjNTFjMmI3MDBjNDgyNTU0MDk4MzBjZTJmNDVmYzZmNDA0MTIwODE3Njg3NGM1ZDA2NDFiYzM4YzM2MWRiNTgwYWQ3ZDY0ZThkOWU0Y2M5MTY=
But both should be same. The c# one is correct, I want the same in the php code as well.

From the PHP docs for hash:
hash ( string $algo , string $data , bool $binary = false ) : string|false
binary
   When set to true, outputs raw binary data. false outputs lowercase hexits.
You're not passing a value for $binary, so it's returning a string of hexadecimal characters.
The C# HashAlgorithm.ComputeHash method on the other hand binary data.
Since you're base64-encoding the result, you're presumably expecting the hash function to return binary data. You therefore need to pass true as the value for $binary:
$signature = base64_encode(hash('sha512', $utf, true));

Convert PHP's dot concatenation of a binary part + string part to C#

I'm working on rewriting a piece of PHP code to C#. This code is used for password hashing. In the first step it produces a string like "password{salt}", than hashes it via sha512 hash algorithm. After that a loop is hashing the combination of the first hash and the salt again for 5000 iterations.
The PHP Code looks like this:
<?php
$password = 'abc';
$salt = 'def';
$salted = $password.'{'.$salt.'}';
$digest = hash('sha512', $salted, true);
for ($i=1; $i<5000; $i++) {
$digest = hash('sha512', $digest.$salted, true);
}
$encodedPassword = base64_encode($digest);
//$encodedPassword contains the final hash code
I was able to get it working without the loop (with just the first hash() call). So the main hashing and base64 encoding is done correctly. I found out that this part is what I cannot manage to rewrite in C#:
$digest.$salted
$digest seems to be a binary representation since PHP's hash() function was used with "true" as the last parameter (see PHP hash - manual). $salted is a string. Both get somehow magically combined by PHP's dot / concat operator. I guess there will be some sort of standard conversion from binary to string under the hood when using the dot operator with a non-string operand.
This is my code so far:
void Main()
{
string password = "abc";
string salt = "def";
string salted = String.Format("{0}{{{1}}}", password, salt);
byte[] digest = hash(salted);
for(int i = 1; i < 1; i++)
{
digest = hash(String.Format("{0}{1}", System.Text.Encoding.UTF8.GetString(digest), salted));
}
var encodedPassword = System.Convert.ToBase64String(digest);
//$encodedPassword should contain the final hash code
}
static byte[] hash(string toHash)
{
System.Security.Cryptography.SHA512 sha512 = new System.Security.Cryptography.SHA512Managed();
return sha512.ComputeHash(System.Text.Encoding.UTF8.GetBytes(toHash));
}
As you see I tried to convert the hash bytes back to a string with System.Text.Encoding.UTF8.GetString() and then append the salt but that doesn't produce the same output as the PHP code.
I would be very happy if someone could help me on this. Thank you very much.

In the PHP version you loop 4999 times, while in the C# version 0. The second problem is that the returned bytes from hash() have no encoding at all.
This should give you the same result as the PHP version:
System.Security.Cryptography.SHA512 sha512 = new System.Security.Cryptography.SHA512Managed();
var saltedUtf8Bytes = System.Text.Encoding.UTF8.GetBytes(salted);
for(int i = 1; i < 5000; i++)
{
digest = sha512.ComputeHash(digest.Concat(saltedUtf8Bytes).ToArray());
}

Encryption, possible base64?

Given the string
KlVkeNK76V27D2MSBOhfNC6eNtA=
This look like base64 encoded. However, I tried using convert to base64 with C# , result is a garbage string.
public static string Base64Encode(string plainText)
{
var plainTextBytes = System.Text.Encoding.UTF8.GetBytes(plainText);
return System.Convert.ToBase64String(plainTextBytes);
}
If I use this:
https://hashkiller.co.uk/sha1-decrypter.aspx
then it give a nicely SHA1 hash:
2a556478d2bbe95dbb0f631204e85f342e9e36d0
Can anyone show me how to decrypt it with C#?
Thanks a lot.

They simply print the hex value of the base64-decoded string:
byte[] bytes = Convert.FromBase64String("KlVkeNK76V27D2MSBOhfNC6eNtA=");
string hexString = new SoapHexBinary(bytes).ToString().ToLowerInvariant();
(where SoapHexBinary is a .NET class that converts byte[] to hex string)

C# vs PHP - They return different HMACSHA256

This is my PHP code:
<?php
$sig_string = "GET&https%3A%2F%2Fapi.pinterest.com%2Fv3%2Fusers%2Farchimede%2Fboards%2F&client_id=987654&timestamp=1391761866";
$secret = "123456";
$sig = hash_hmac("sha256", $sig_string, $secret);
echo $sig;
?>
which returns (correctly) a7918aec50919915f3cefed8622ddbe35448c8f71a54ad115828f07a05930f4c
Now, I want to translate this function inside C#. Code:
signature_base_string = "GET&https%3A%2F%2Fapi.pinterest.com%2Fv3%2Fusers%2Farchimede%2Fboards%2F&client_id=987654&timestamp=1391761866";
signing_key = "123456";
var encoding = new System.Text.ASCIIEncoding();
byte[] keyByte = encoding.GetBytes(signing_key);
byte[] messageBytes = encoding.GetBytes(signature_base_string);
using (var hmacsha256 = new HMACSHA256(keyByte))
{
byte[] hashmessage = hmacsha256.ComputeHash(messageBytes);
Response.Write(Convert.ToBase64String(hashmessage));
}
but it retuns p5GK7FCRmRXzzv7YYi3b41RIyPcaVK0RWCjwegWTD0w=
Why two different results? Whats wrong in the C# code?

PHP encodes the result in hexadecimal and c# encodes that in base64. But the are same.
Change this line:
Response.Write(Convert.ToBase64String(hashmessage));
To this:
Response.Write(BitConverter.ToString(hashmessage).Replace("-", "").ToLower());
to have the result in hexadecimal encoding.

They are the same:
The result from .NET C# is p5GK7FCRmRXzzv7YYi3b41RIyPcaVK0RWCjwegWTD0w=. This is a base64 string.
You can convert it to hexadecimal using this tool for example. And you'll get the same as PHP after converting:
A7918AEC50919915F3CEFED8622DDBE35448C8F71A54AD115828F07A05930F4C

PHP MD5 not matching C# MD5

I have a hashing method in C# that looks like:
MD5CryptoServiceProvider md5 = new MD5CryptoServiceProvider();
byte[] raw_input = Encoding.UTF32.GetBytes("hello");
byte[] raw_output = md5.ComputeHash(raw_input);
string output = "";
foreach (byte myByte in raw_output)
output += myByte.ToString("X2");
return output;
How can I implement this in PHP? Doing the following produces a different hash digest...
$output = hash('md5', 'hello');

PHP
This PHP code will do:
<?php
$str = "admin";
$strUtf32 = mb_convert_encoding($str, "UTF-32LE");
echo md5($strUtf32);
?>
This code outputs "1e3fcd02b1547f847cb7fc3add4484a5"

You need to find out which encoding PHP is using to convert your string to text. It's very unlikely that it's using UTF-32. It may well be using the platform default encoding, or possibly UTF-8.
using (MD5 md5 = MD5.Create())
{
byte[] input = Encoding.UTF8.GetBytes("hello");
byte[] hash = md5.ComputeHash(input);
return BitConverter.ToString(hash).Replace("-", "");
}
(This is the problem with languages/platforms which treat strings as binary data all over the place - it doesn't make it clear what's going on. There has to be a conversion to bytes here, as MD5 is defined for bytes, not Unicode characters. In the C# code you're doing it explicitly... in the PHP it's implicit and poorly documented.)
EDIT: If you've got to change the PHP, you could try this:
$text = mb_convert_encoding($text, "UTF-32LE");
$output = md5($text)
It depends whether PHP supports UTF-32 though...

When you apply md5 to Encoding.UTF32.GetBytes("admin");, that's same as
echo hash( "md5","a\0\0\0d\0\0\0m\0\0\0i\0\0\0n\0\0\0");
//1e3fcd02b1547f847cb7fc3add4484a5
In php.
You need to convert your string to UTF32-LE in PHP:
echo md5( mb_convert_encoding( "admin", "UTF-32LE" ) );
//1e3fcd02b1547f847cb7fc3add4484a5