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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));

Unable to encode byte array to UTF8 then decode it back to bytes

I'm trying to convert a byte array to a string, then at a later time convert those strings back to a byte array, but I'm getting some inconsistent results.
var salt = System.Text.Encoding.UTF8.GetString(encryptedPassword.Salt);
var key = System.Text.Encoding.UTF8.GetString(encryptedPassword.Key);
...
var saltBytes = System.Text.Encoding.UTF8.GetBytes(salt);
var keyBytes = System.Text.Encoding.UTF8.GetBytes(key);
In this case, the original salt and key are both byte[20], but the new ones are not equal (salt being a byte[36], key a byte [41], both with totally different values).

Basically what #DourHighArch said. You can go string->binary->string, but you can't expect to be able to go binary->string->binary using text encoding.
For what you are doing, you probably want to use something like base64 encoding. So you could write it like this:
var salt = Convert.ToBase64String(encryptedPassword.Salt);
var key = Convert.ToBase64String(encryptedPassword.Key);
...
var saltBytes = Convert.FromBase64String(salt);
var keyBytes = Convert.FromBase64String(key);

Convert C# to Ruby - MD5 and Base 64 a String

I have this code that I need to convert to ruby, this snippet is to create a security key used for a particular API. The string that I am encrypting is a JSON object.
Should I use Digest::MD5.hexdigest() or Digest::MD5.digest()?
C# Code
string strResponse = "[{\"Key\":\"BookNumber\", \"Value\"=>\"BJAK123\"},{\"Key\"=>\"AuthorCode\", \"Value\"=>\"BNA123\"}]";
using (MD5 md5 = MD5.Create())
{
byte[] bPayload = Encoding.UTF8.GetBytes(strPayload);
byte[] bPayloadHash = md5.ComputeHash(bPayload);
strPayloadBase64 = Convert.ToBase64String(bPayloadHash);
}
Ruby Code
payload = [{"Key"=>"BookNumber", "Value"=>"BJAK123"},{"Key"=>"AuthorCode", "Value"=>"BNA123"}]
utf8_params = payload.to_json.force_encoding("iso-8859-1").force_encoding("utf-8")
payload_base64 = Base64.encode64(Digest::MD5.hexdigest(utf8_params))

Use
payload_base64 = Digest::MD5.base64digest(utf8_params)
as Digest::MD5.hexdigest produces a hex string of digest, whereas C# code is performing base64 encoding of the digest.

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

Generate a PHP UTF-16 SHA1 hash to match C# method

I'm trying to replicate some C# code in PHP5 and am having some difficulties.
The C# code is as following, and it is important to note that it cannot be changed:
string s = strToHash;
UnicodeEncoding encoding = new UnicodeEncoding();
byte[] bytes = encoding.GetBytes(s);
SHA1Managed managed = new SHA1Managed();
bytes = encoding.GetBytes(Convert.ToBase64String(managed.ComputeHash(bytes)) + "Space");
return Convert.ToBase64String(managed.ComputeHash(bytes));
The PHP code I've written to replicate this is as follows:
utfString = mb_convert_encoding($strToHash,"UTF-16");
hashTag = sha1($utfString,true);
base64Tag = base64_encode($hashTag);
encodedBase64Tag = mb_convert_encoding($base64Tag."Space","UTF-16");
base64EncodedAgain = base64_encode($encodedBase64Tag);
echo $base64EncodedAgain
However, the two outputs don't match up.
I believe this is because the SHA1 method in PHP works on ASCII encoded strings, not the encoding actually used by the passed in string.
I would like to get this to work, and I can't achieve it by altering the c# code (although no-doubt that would be the easiest fix).
Please can any advise on some ideas?
OK, I have altered the code following Artefacto's advice, and it still isn't working as expected.
The PHP Code now looks like this:
$utfString = "\xFF\xFE".mb_convert_encoding($strToHash,"UTF-16LE");
$hashTag = sha1($utfString,true);
$base64Tag = base64_encode($hashTag);
$encodedBase64Tag = "\xFF\xFE".mb_convert_encoding($base64Tag."Space","UTF-16LE");
$hashedAgain = sha1($encodedBase64Tag,true);
$base64EncodedAgain = base64_encode($hashedAgain);
echo $base64EncodedAgain."<Br/>";
And the outputed value of this method is:
1/Y5MCzI8vDJqc456YIicpwoyy0=
However, from the C# code, the value is this:
VPf7BhT1ksAfWbzeJw35g+bVKwY=

Well, try this code:
$utfString = mb_convert_encoding($strToHash,"UTF-16");
$hashTag = sha1($utfString,true);
$base64Tag = base64_encode($hashTag);
$encodedBase64Tag = mb_convert_encoding($base64Tag."Space","UTF-16");
$base64EncodedAgain = base64_encode(sha1($encodedBase64Tag, true));
echo $base64EncodedAgain
Because you miss one sha1 call.
Update
Now this code should work:
$utfString = mb_convert_encoding($strToHash,"UTF-16LE");
$hashTag = sha1($utfString,true);
$base64Tag = base64_encode($hashTag);
$encodedBase64Tag = mb_convert_encoding($base64Tag."Space","UTF-16LE");
$hashedAgain = sha1($encodedBase64Tag,true);
$base64EncodedAgain = base64_encode($hashedAgain);
echo $base64EncodedAgain . "<br />";

The docs for the no-arg constructor of UnicodeEncoding say this:
This constructor creates an instance that uses the little endian byte order, provides a Unicode byte order mark, and does not throw an exception when an invalid encoding is detected.
Now, mb_convert_encoding assumes "UTF-16" as "UTF-16BE" (big-endian). It also does not provide a BOM. Therefore, you must do instead:
$utfString = "\xFF\xFE" . mb_convert_encoding($strToHash,"UTF-16LE");
/* ...*/
$encodedBase64Tag = "\xFF\xFE" . mb_convert_encoding($base64Tag."Space","UTF-16LE");
As Paja pointed out, you're also missing a call to sha1.

This code should work...
$utfString = mb_convert_encoding($strToHash,"UTF-16LE");
$hashTag = sha1($utfString,true);
$base64Tag = base64_encode($hashTag);
echo $base64Tag;