add support for the length of MD5 hash result .

README.md

@@ -139,6 +139,13 @@ Install-Package NETCore.Encrypt -Version 2.0.2
 
   ```
 
+  ```csharp
+
+  var srcString = "Md5 hash";
+  var hashed = EncryptProvider.Md5(srcString, MD5Length.L16);
+
+  ```
+
   ## SHA
 
   - #### SHA1

src/NETCore.Encrypt/EncryptProvider.cs

@@ -423,30 +423,35 @@ public static RSAKey CreateRsaKey(RsaSize rsaSize = RsaSize.R2048)
         #endregion
 
         #region MD5
-
         /// <summary>
         /// MD5 hash
         /// </summary>
-        /// <param name="srcString">The string to be encrypted</param>
+        /// <param name="srcString">The string to be encrypted.</param>
+        /// <param name="length">The length of hash result , default value is <see cref="MD5Length.L32"/>.</param>
         /// <returns></returns>
-        public static string Md5(string srcString)
+        public static string Md5(string srcString, MD5Length length = MD5Length.L32)
         {
             Check.Argument.IsNotEmpty(srcString, nameof(srcString));
 
+            string str_md5_out = string.Empty;
             using (MD5 md5 = MD5.Create())
             {
                 byte[] bytes_md5_in = Encoding.UTF8.GetBytes(srcString);
                 byte[] bytes_md5_out = md5.ComputeHash(bytes_md5_in);
-                string str_md5_out = BitConverter.ToString(bytes_md5_out);
+
+                str_md5_out = length == MD5Length.L32
+                    ? BitConverter.ToString(bytes_md5_out) 
+                    : BitConverter.ToString(bytes_md5_out, 4, 8);
+
                 str_md5_out = str_md5_out.Replace("-", "");
                 return str_md5_out;
             }
-        }
+        }        
         #endregion
 
         #region HMACMD5
         /// <summary>
-        /// MD5 hash
+        /// HMACMD5 hash
         /// </summary>
         /// <param name="srcString">The string to be encrypted</param>
         /// <param name="key">encrypte key</param>

src/NETCore.Encrypt/Internal/MD5Length.cs

@@ -0,0 +1,8 @@
+namespace NETCore.Encrypt
+{
+    public enum MD5Length
+    {
+        L16 = 16,
+        L32 = 32
+    }
+}

test/NETCore.Encrypt.Tests/MD5_Tests.cs

@@ -25,5 +25,16 @@ public void MD5_Error_Test()
         {
             Assert.Throws<ArgumentException>(() => EncryptProvider.Md5(string.Empty));
         }
+
+        [Fact(DisplayName = "MD5 with length success test")]
+        public void MD5_With_Length_Success_Test()
+        {
+            var srcString = "Md5 test";
+
+            var hashed = EncryptProvider.Md5(srcString, MD5Length.L16);
+
+            Assert.NotEmpty(hashed);
+            Assert.Equal("69c6ecadb32f5492", hashed.ToLower());
+        }
     }
 }