Use different hash calculation for Qt work items

Will now calculate the hash of Qt work items (i.e. MSBuild items that
represent in-build processing with Qt tools moc, rcc, etc.) using a
a combination of Deflate and Base64. Previously, the hash relied on the
SHA1 implementation in .NET cryptography. The new approach entails a
slight (i.e. non-significant) performance degradation, and has some
advantages over using SHA1:
  * Deflate's lossless compression eliminates the (extremely unlikely)
    possibility of an hash collision.
  * Avoids any current or future restrictions imposed on the use of
    cryptographic functions -- as is the case with the enforcement of
    FIPS compliance (cf. bug report).

Task-number: QTVSADDINBUG-618
Change-Id: I70017cacfb093377bed07da207fd2e10ddf5fe2b
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>

2 files changed, 12 insertions, 9 deletions

diff --git a/src/qtmsbuild/qt_globals.targets b/src/qtmsbuild/qt_globals.targets
index e9eaf5ca..972047a5 100644
--- a/src/qtmsbuild/qt_globals.targets
+++ b/src/qtmsbuild/qt_globals.targets
@@ -118,7 +118,7 @@
 
     <!--
     ///////////////////////////////////////////////////////////////////////////////////////////////
-    // Calculate hash (SHA1) for the requested work item, based on its associated tool and options
+    // Calculate hash for the requested work item, based on its associated tool and options
     // -->
     <GetItemHash Condition="'@(QtWork)' != ''"
       Item="@(QtWork)" Keys="Identity;WorkType;ToolPath;Options">
diff --git a/src/qtmsbuild/qt_tasks.targets b/src/qtmsbuild/qt_tasks.targets
index 5eb961c3..fc65771c 100644
--- a/src/qtmsbuild/qt_tasks.targets
+++ b/src/qtmsbuild/qt_tasks.targets
@@ -39,11 +39,11 @@
   /////////////////////////////////////////////////////////////////////////////////////////////////
   /// TASK GetItemHash
   /////////////////////////////////////////////////////////////////////////////////////////////////
-  // Calculate an hash code (SHA1) for an item, given a list of metadata to use as key
+  // Calculate an hash code (Deflate + Base64) for an item, given a list of metadata to use as key
   // Parameters:
   //      in ITaskItem Item: item for which the hash will be calculated
   //      in string[]  Keys: list of names of the metadata to use as item key
-  //     out string    Hash: hash code (SHA1 in hexadecimal format)
+  //     out string    Hash: hash code (Base64 representation of Deflate'd UTF-8 item key)
   // -->
   <UsingTask TaskName="GetItemHash"
     TaskFactory="CodeTaskFactory" AssemblyFile="$(MSBuildToolsPath)\Microsoft.Build.Tasks.v4.0.dll">
@@ -55,14 +55,17 @@
     <Task>
       <Using Namespace="System"/>
       <Using Namespace="System.Text"/>
-      <Using Namespace="System.Security.Cryptography"/>
+      <Using Namespace="System.IO"/>
+      <Using Namespace="System.IO.Compression"/>
       <Code Type="Fragment" Language="cs">
         <![CDATA[
-            var data = string.Concat(Keys.OrderBy(x => x)
-                .Select(x => string.Format("[{0}={1}]", x, Item.GetMetadata(x))));
-            using (var sha1 = new SHA1Managed()) {
-                Hash = string.Concat(sha1.ComputeHash(Encoding.UTF8.GetBytes(data))
-                    .Select(x => x.ToString("x2")));
+            var data = Encoding.UTF8.GetBytes(string.Concat(Keys.OrderBy(x => x)
+                .Select(x => string.Format("[{0}={1}]", x, Item.GetMetadata(x))))
+                .ToUpper());
+            using (var dataZipped = new MemoryStream()) {
+                using (var zip = new DeflateStream(dataZipped, CompressionLevel.Fastest))
+                    zip.Write(data, 0, data.Length);
+                Hash = Convert.ToBase64String(dataZipped.ToArray());
             }
         ]]>
       </Code>