如何写出安全的API接口？接口参数加密签名设计思路

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace test3
{
public class SampleCode
{
public static string test()
{
int _timestamp = ;
var param = new SortedDictionary<string, string>(new AsciiComparer());
param.Add("z", "ZZZ");
param.Add("a", "AAA");
param.Add("Z", "zzz");
param.Add("A", "aaa");
param.Add("", "贰");
param.Add("", "壹");
param.Add("_appid", "club");
param.Add("_timestamp", _timestamp.ToString());
string _sign = GetSign(param);
string urlParam = string.Join("&", param.Select(i => i.Key + "=" + i.Value));
string url = "http://api.demo.com/dog/add?" + urlParam + "&_sign=" + _sign;
return url;
}
public static string GetSign(SortedDictionary<string, string> paramList, string appKey = "test")
{
paramList.Remove("_sign");
StringBuilder sb = new StringBuilder(appKey);
foreach (var p in paramList)
sb.Append(p.Key).Append(p.Value);
sb.Append(appKey);
return GetMD5(sb.ToString());
}
public static string GetMD5(string str)
{
if (string.IsNullOrEmpty(str))
return str;
var sb = new StringBuilder();
var md5 = System.Security.Cryptography.MD5.Create();
var output = md5.ComputeHash(Encoding.UTF8.GetBytes(str));
for (int i = ; i < output.Length; i++)
sb.Append(output[i].ToString("X").PadLeft(, ''));
return sb.ToString();
}
}
/// <summary>
/// 基于ASCII码排序规则的String比较器
/// Author：HeDaHong
/// </summary>
public class AsciiComparer : System.Collections.Generic.IComparer<string>
{
public int Compare(string a, string b)
{
if (a == b)
return ;
else if (string.IsNullOrEmpty(a))
return -;
else if (string.IsNullOrEmpty(b))
return ;
if (a.Length <= b.Length)
{
for (int i = ; i < a.Length; i++)
{
if (a[i] < b[i])
return -;
else if (a[i] > b[i])
return ;
else
continue;
}
return a.Length == b.Length ? : -;
}
else
{
for (int i = ; i < b.Length; i++)
{
if (a[i] < b[i])
return -;
else if (a[i] > b[i])
return ;
else
continue;
}
return ;
}
}
}
}