这是一个使用SHA512和随机盐的基本哈希和盐方法，将盐添加到哈希之前。
private static string HashAndSalt(string plaintext)
{
    var chars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890";
    using var hasher = SHA512.Create();
    var random = new Random();
    var ciphertextBytes = hasher.ComputeHash(Encoding.UTF8.GetBytes(plaintext));
    var ciphertextB64 = Convert.ToBase64String(ciphertextBytes);
    var salt = new string(Enumerable.Repeat(chars, 8).Select(s => s[random.Next(s.Length)]).ToArray());
    var ciphertext = salt + ':' + ciphertextB64;
    return ciphertext;
}

你需要将你的`SecureString`转换为普通的`string`。使用`SecureString`已经过时，不应再使用。正如评论中提到的，你应该考虑使用专用的密码哈希算法，如：
- PBKDF2
- Argon2
- Bcrypt
- Scrypt
以下是使用`Bcrypt` 的示例 - 它并不太复杂。
首先，获取这个NuGet包：`BCrypt.Net-Next`
private static string BcryptHash(string plaintext)
{
    var ciphertext = BCrypt.Net.BCrypt.HashPassword(plaintext, 12);
    return ciphertext;
}
但是，你不能像SHA512一样在用户尝试进行身份验证时比较哈希值。你需要使用Bcrypt的'Verify'函数。
private static bool BcryptVerify(string plaintext)
{
    return BCrypt.Net.BCrypt.Verify(plaintext, hashedPassword);
}
其中，plaintext是你从用户输入中收到的“plaintext”密码，hashedPassword是你从存储初始ciphertext的数据库中检索到的哈希值。
希望这有所帮助。
<details>
<summary>英文:</summary>
Here is a basic hash and salt method using SHA512 and a random salt prepended to the hash.
    private static string HashAndSalt(string plaintext)
    {
        var chars = &quot;abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890&quot;;
    
        using var hasher = SHA512.Create();
        var random = new Random();
    
        var ciphertextBytes = hasher.ComputeHash(Encoding.UTF8.GetBytes(plaintext));
        var ciphertextB64 = Convert.ToBase64String(ciphertextBytes);
        var salt = new string(Enumerable.Repeat(chars, 8).Select(s =&gt; s[random.Next(s.Length)]).ToArray());
    
        var ciphertext = salt + &#39;:&#39; + ciphertextB64;
    
        return ciphertext;
    } 
You will need to convert your `SecureString` to a normal `string`. Using a `SecureString` is obsolete and should not be used anymore. As the comments mentioned you should look into a dedicated password hashing algorithm such as:
 - PBKDF2
 - Argon2
 - Bcrypt
 - Scrypt
Here is an example using `Bcrypt` - it is not too complicated.
First, grab this NuGet package: `BCrypt.Net-Next`
    private static string BcryptHash(string plaintext)
    {
        var ciphertext = BCrypt.Net.BCrypt.HashPassword(plaintext, 12);
        return ciphertext;
    } 
You can&#39;t however compare the hashes when a user tries to authenticate as you can with SHA512. You need to use Bcrypts &#39;Verify&#39; function.
    private static bool BcryptVerify(string plaintext)
    {
        return BCrypt.Net.BCrypt.Verify(plaintext, hashedPassword);
    } 
Where the plaintext is the `plaintext` password you receive from user input and the `hashedPassword` being the hash you retrieved from the database where the initial ciphertext was stored.
Hope this helps.
</details>