Add archive-level IsEncrypted flag

src/SharpCompress/Archives/AbstractArchive.cs

@@ -161,6 +161,11 @@ public abstract class AbstractArchive<TEntry, TVolume> : IArchive, IArchiveExtra
     /// </summary>
     public virtual bool IsSolid => false;
 
+    /// <summary>
+    /// Archive is ENCRYPTED (this means the Archive has password-protected files).
+    /// </summary>
+    public virtual bool IsEncrypted => false;
+
     /// <summary>
     /// The archive can find all the parts of the archive needed to fully extract the archive.  This forces the parsing of the entire archive.
     /// </summary>

src/SharpCompress/Archives/Rar/RarArchive.cs

@@ -84,6 +84,11 @@ public class RarArchive : AbstractArchive<RarArchiveEntry, RarVolume>
 
     public override bool IsSolid => Volumes.First().IsSolidArchive;
 
+    public override bool IsEncrypted =>
+        Entries
+            .Where(x => !x.IsDirectory)
+            .Any(file => file.IsEncrypted);
+
     public virtual int MinVersion => Volumes.First().MinVersion;
     public virtual int MaxVersion => Volumes.First().MaxVersion;
 

src/SharpCompress/Archives/SevenZip/SevenZipArchive.cs

@@ -205,6 +205,11 @@ public class SevenZipArchive : AbstractArchive<SevenZipArchiveEntry, SevenZipVol
             .GroupBy(x => x.FilePart.Folder)
             .Any(folder => folder.Count() > 1);
 
+    public override bool IsEncrypted =>
+        Entries
+            .Where(x => !x.IsDirectory)
+            .Any(file => file.IsEncrypted);
+
     public override long TotalSize =>
         _database?._packSizes.Aggregate(0L, (total, packSize) => total + packSize) ?? 0;