From 917a2b78dde53442104703c0c4a6ea75608a21d5 Mon Sep 17 00:00:00 2001
From: Jason Prothero <jason@proworks.com>
Date: Mon, 12 Jun 2017 13:44:42 -0700
Subject: [PATCH] Added RFC 4122 compliant GUID support to the ToGuid() method
 on StrringExtensions.cs.  Verified the SHA1 hash works with the ToGuid()
 method via unit tests.

---
 src/Umbraco.Core/StringExtensions.cs | 79 +++++++++++++++++++++++++++-
 1 file changed, 78 insertions(+), 1 deletion(-)

diff --git a/src/Umbraco.Core/StringExtensions.cs b/src/Umbraco.Core/StringExtensions.cs
index f540305325..dba7f2cfee 100644
--- a/src/Umbraco.Core/StringExtensions.cs
+++ b/src/Umbraco.Core/StringExtensions.cs
@@ -1470,7 +1470,84 @@ namespace Umbraco.Core
         /// <returns></returns>
         internal static Guid ToGuid(this string text)
         {
-            return new Guid(text.GenerateHash());
+            return CreateGuidFromHash(UrlNamespace,
+                                        text,
+                                        CryptoConfig.AllowOnlyFipsAlgorithms
+                                            ? 5     // SHA1
+                                            : 3);   // MD5
+        }
+
+        /// <summary>
+        /// The namespace for URLs (from RFC 4122, Appendix C).
+        /// 
+        /// See <a href="http://www.ietf.org/rfc/rfc4122.txt">RFC 4122</a>
+        /// </summary>
+        internal static readonly Guid UrlNamespace = new Guid("6ba7b811-9dad-11d1-80b4-00c04fd430c8");
+
+        /// <summary>
+        /// Creates a name-based UUID using the algorithm from RFC 4122 §4.3.
+        /// 
+        /// See <a href="https://github.com/LogosBible/Logos.Utility/blob/master/src/Logos.Utility/GuidUtility.cs#L34">GuidUtility.cs</a> for original implementation.
+        /// </summary>
+        /// <param name="namespaceId">The ID of the namespace.</param>
+        /// <param name="name">The name (within that namespace).</param>
+        /// <param name="version">The version number of the UUID to create; this value must be either
+        /// 3 (for MD5 hashing) or 5 (for SHA-1 hashing).</param>
+        /// <returns>A UUID derived from the namespace and name.</returns>
+        /// <remarks>See <a href="http://code.logos.com/blog/2011/04/generating_a_deterministic_guid.html">Generating a deterministic GUID</a>.</remarks>
+        internal static Guid CreateGuidFromHash(Guid namespaceId, string name, int version)
+        {
+            if (name == null)
+                throw new ArgumentNullException("name");
+            if (version != 3 && version != 5)
+                throw new ArgumentOutOfRangeException("version", "version must be either 3 or 5.");
+
+            // convert the name to a sequence of octets (as defined by the standard or conventions of its namespace) (step 3)
+            // ASSUME: UTF-8 encoding is always appropriate
+            byte[] nameBytes = Encoding.UTF8.GetBytes(name);
+
+            // convert the namespace UUID to network order (step 3)
+            byte[] namespaceBytes = namespaceId.ToByteArray();
+            SwapByteOrder(namespaceBytes);
+
+            // comput the hash of the name space ID concatenated with the name (step 4)
+            byte[] hash;
+            using (HashAlgorithm algorithm = version == 3 ? (HashAlgorithm)MD5.Create() : SHA1.Create())
+            {
+                algorithm.TransformBlock(namespaceBytes, 0, namespaceBytes.Length, null, 0);
+                algorithm.TransformFinalBlock(nameBytes, 0, nameBytes.Length);
+                hash = algorithm.Hash;
+            }
+
+            // most bytes from the hash are copied straight to the bytes of the new GUID (steps 5-7, 9, 11-12)
+            byte[] newGuid = new byte[16];
+            Array.Copy(hash, 0, newGuid, 0, 16);
+
+            // set the four most significant bits (bits 12 through 15) of the time_hi_and_version field to the appropriate 4-bit version number from Section 4.1.3 (step 8)
+            newGuid[6] = (byte)((newGuid[6] & 0x0F) | (version << 4));
+
+            // set the two most significant bits (bits 6 and 7) of the clock_seq_hi_and_reserved to zero and one, respectively (step 10)
+            newGuid[8] = (byte)((newGuid[8] & 0x3F) | 0x80);
+
+            // convert the resulting UUID to local byte order (step 13)
+            SwapByteOrder(newGuid);
+            return new Guid(newGuid);
+        }
+
+        // Converts a GUID (expressed as a byte array) to/from network order (MSB-first).
+        internal static void SwapByteOrder(byte[] guid)
+        {
+            SwapBytes(guid, 0, 3);
+            SwapBytes(guid, 1, 2);
+            SwapBytes(guid, 4, 5);
+            SwapBytes(guid, 6, 7);
+        }
+
+        private static void SwapBytes(byte[] guid, int left, int right)
+        {
+            byte temp = guid[left];
+            guid[left] = guid[right];
+            guid[right] = temp;
         }
     }
 }