Throw PNSE for GCM/CCM on unsupported platforms

Author: vcsjones

src/libraries/System.Security.Cryptography.Algorithms/src/System/Security/Cryptography/AesCcm.cs

@@ -14,12 +14,16 @@ public sealed partial class AesCcm : IDisposable
 
         public AesCcm(ReadOnlySpan<byte> key)
         {
+            ThrowIfNotSupported();
+
             AesAEAD.CheckKeySize(key.Length);
             ImportKey(key);
         }
 
         public AesCcm(byte[] key)
         {
+            ThrowIfNotSupported();
+
             if (key == null)
                 throw new ArgumentNullException(nameof(key));
 
@@ -76,5 +80,13 @@ private static void CheckParameters(
             if (!tag.Length.IsLegalSize(TagByteSizes))
                 throw new ArgumentException(SR.Cryptography_InvalidTagLength, nameof(tag));
         }
+
+        private static void ThrowIfNotSupported()
+        {
+            if (!IsSupported)
+            {
+                throw new PlatformNotSupportedException(SR.Format(SR.Cryptography_AlgorithmNotSupported, nameof(AesCcm)));
+            }
+        }
     }
 }

src/libraries/System.Security.Cryptography.Algorithms/src/System/Security/Cryptography/AesGcm.cs

@@ -15,12 +15,16 @@ public sealed partial class AesGcm : IDisposable
 
         public AesGcm(ReadOnlySpan<byte> key)
         {
+            ThrowIfNotSupported();
+
             AesAEAD.CheckKeySize(key.Length);
             ImportKey(key);
         }
 
         public AesGcm(byte[] key)
         {
+            ThrowIfNotSupported();
+
             if (key == null)
                 throw new ArgumentNullException(nameof(key));
 
@@ -77,5 +81,13 @@ private static void CheckParameters(
             if (!tag.Length.IsLegalSize(TagByteSizes))
                 throw new ArgumentException(SR.Cryptography_InvalidTagLength, nameof(tag));
         }
+
+        private static void ThrowIfNotSupported()
+        {
+            if (!IsSupported)
+            {
+                throw new PlatformNotSupportedException(SR.Format(SR.Cryptography_AlgorithmNotSupported, nameof(AesGcm)));
+            }
+        }
     }
 }

src/libraries/System.Security.Cryptography.Algorithms/tests/AesCcmTests.cs

@@ -678,6 +678,17 @@ public static IEnumerable<object[]> GetNistCcmTestCasesWithNonEmptyPT()
 
     public class AesCcmIsSupportedTests
     {
+        public static bool RuntimeSaysIsNotSupported => !AesCcm.IsSupported;
+
+        [ConditionalFact(nameof(RuntimeSaysIsNotSupported))]
+        public static void CtorThrowsPNSEIfNotSupported()
+        {
+            byte[] key = RandomNumberGenerator.GetBytes(256 / 8);
+
+            Assert.Throws<PlatformNotSupportedException>(() => new AesCcm(key));
+            Assert.Throws<PlatformNotSupportedException>(() => new AesCcm(key.AsSpan()));
+        }
+
         [Fact]
         public static void CheckIsSupported()
         {

src/libraries/System.Security.Cryptography.Algorithms/tests/AesGcmTests.cs

@@ -839,6 +839,17 @@ private static IEnumerable<AEADTest> GetNistTests()
 
     public class AesGcmIsSupportedTests
     {
+        public static bool RuntimeSaysIsNotSupported => !AesGcm.IsSupported;
+
+        [ConditionalFact(nameof(RuntimeSaysIsNotSupported))]
+        public static void CtorThrowsPNSEIfNotSupported()
+        {
+            byte[] key = RandomNumberGenerator.GetBytes(256 / 8);
+
+            Assert.Throws<PlatformNotSupportedException>(() => new AesGcm(key));
+            Assert.Throws<PlatformNotSupportedException>(() => new AesGcm(key.AsSpan()));
+        }
+
         [Fact]
         public static void CheckIsSupported()
         {