Further peer review fixes

Author: dgarske

wrapper/CSharp/wolfCrypt-Test/wolfCrypt-Test.cs

@@ -996,6 +996,23 @@ private static void hpke_test(wolfcrypt.HpkeKem kem,
             }
             Console.WriteLine("HPKE convenience overload test PASSED.");
 
+            /* Empty plaintext round-trip - native API accepts ptSz == 0 */
+            Console.WriteLine("Testing HpkeSealBase/OpenBase with empty plaintext...");
+            byte[] emptyPt = new byte[0];
+            byte[] encEmpty = wolfcrypt.HpkeSealBase(hpke, receiverKey,
+                info, aad, emptyPt, kem);
+            if (encEmpty == null)
+            {
+                throw new Exception("HpkeSealBase with empty plaintext failed");
+            }
+            byte[] decEmpty = wolfcrypt.HpkeOpenBase(hpke, receiverKey,
+                encEmpty, info, aad, kem);
+            if (decEmpty == null || decEmpty.Length != 0)
+            {
+                throw new Exception("HpkeOpenBase with empty plaintext: round-trip failed");
+            }
+            Console.WriteLine("Empty plaintext round-trip test PASSED.");
+
             /* Negative test: tampered ciphertext should fail */
             Console.WriteLine("Testing HpkeOpenBase with tampered ciphertext...");
             byte[] tampered = (byte[])encCiphertext.Clone();

wrapper/CSharp/wolfSSL_CSharp/wolfCrypt.cs

@@ -20,7 +20,10 @@
  */
 
 using System;
+using System.Collections.Generic;
+#if !WindowsCE
 using System.Collections.Concurrent;
+#endif
 using System.Runtime.InteropServices;
 using System.Security.Cryptography;
 using System.Text;
@@ -3289,9 +3292,53 @@ private struct HpkeContextState
             public IntPtr rng;
             public HpkeKem kem;
         }
+
+#if WindowsCE
+        /* .NET Compact Framework / Windows CE does not provide
+         * System.Collections.Concurrent, so fall back to a plain Dictionary
+         * guarded by an explicit lock. */
+        private static readonly Dictionary<IntPtr, HpkeContextState> hpkeContexts =
+            new Dictionary<IntPtr, HpkeContextState>();
+        private static readonly object hpkeContextsLock = new object();
+
+        private static void HpkeContextStore(IntPtr hpke, HpkeContextState state)
+        {
+            lock (hpkeContextsLock) { hpkeContexts[hpke] = state; }
+        }
+        private static bool HpkeContextTryGet(IntPtr hpke, out HpkeContextState state)
+        {
+            lock (hpkeContextsLock) { return hpkeContexts.TryGetValue(hpke, out state); }
+        }
+        private static bool HpkeContextTryRemove(IntPtr hpke, out HpkeContextState state)
+        {
+            lock (hpkeContextsLock)
+            {
+                if (hpkeContexts.TryGetValue(hpke, out state))
+                {
+                    hpkeContexts.Remove(hpke);
+                    return true;
+                }
+                return false;
+            }
+        }
+#else
         private static readonly ConcurrentDictionary<IntPtr, HpkeContextState> hpkeContexts =
             new ConcurrentDictionary<IntPtr, HpkeContextState>();
 
+        private static void HpkeContextStore(IntPtr hpke, HpkeContextState state)
+        {
+            hpkeContexts[hpke] = state;
+        }
+        private static bool HpkeContextTryGet(IntPtr hpke, out HpkeContextState state)
+        {
+            return hpkeContexts.TryGetValue(hpke, out state);
+        }
+        private static bool HpkeContextTryRemove(IntPtr hpke, out HpkeContextState state)
+        {
+            return hpkeContexts.TryRemove(hpke, out state);
+        }
+#endif
+
         /// <summary>
         /// Get the enc (encapsulated key) length for a given KEM
         /// </summary>
@@ -3355,7 +3402,7 @@ public static IntPtr HpkeInit(HpkeKem kem, HpkeKdf kdf, HpkeAead aead)
                     return IntPtr.Zero;
                 }
 
-                hpkeContexts[hpke] = new HpkeContextState { rng = rng, kem = kem };
+                HpkeContextStore(hpke, new HpkeContextState { rng = rng, kem = kem });
             }
             catch (Exception e)
             {
@@ -3392,7 +3439,7 @@ public static IntPtr HpkeGenerateKeyPair(IntPtr hpke)
                 }
 
                 HpkeContextState state;
-                if (!hpkeContexts.TryGetValue(hpke, out state) || state.rng == IntPtr.Zero)
+                if (!HpkeContextTryGet(hpke, out state) || state.rng == IntPtr.Zero)
                 {
                     log(ERROR_LOG, "HPKE generate keypair: no RNG associated with context");
                     return IntPtr.Zero;
@@ -3527,7 +3574,7 @@ public static void HpkeFree(IntPtr hpke)
             if (hpke != IntPtr.Zero)
             {
                 HpkeContextState state;
-                if (hpkeContexts.TryRemove(hpke, out state) && state.rng != IntPtr.Zero)
+                if (HpkeContextTryRemove(hpke, out state) && state.rng != IntPtr.Zero)
                 {
                     RandomFree(state.rng);
                 }
@@ -3558,7 +3605,9 @@ public static byte[] HpkeSealBase(IntPtr hpke, IntPtr ephemeralKey, IntPtr recei
                     log(ERROR_LOG, "HPKE seal base: invalid parameter");
                     return null;
                 }
-                if (plaintext == null || plaintext.Length == 0)
+                /* Native wc_HpkeSealBase only requires plaintext to be non-NULL;
+                 * ptSz == 0 is valid (output is just the AEAD tag). */
+                if (plaintext == null)
                 {
                     log(ERROR_LOG, "HPKE seal base: invalid plaintext");
                     return null;