Simplify throwing exceptions for incorrect encryption length

src/libraries/System.Security.Cryptography.Primitives/src/Resources/Strings.resx

@@ -123,8 +123,8 @@
   <data name="Cryptography_PlaintextTooLarge" xml:space="preserve">
     <value>The specified plaintext size is too large.</value>
   </data>
-  <data name="Cryptography_EncryptedIncorrectPadding" xml:space="preserve">
-    <value>TryEncryptEcbCore unexpectedly produced a ciphertext which has the incorrect amount of padding.</value>
+  <data name="Cryptography_EncryptedIncorrectLength" xml:space="preserve">
+    <value>{0} unexpectedly produced a ciphertext with the incorrect length.</value>
   </data>
   <data name="NotSupported_SubclassOverride" xml:space="preserve">
     <value>Method not supported. Derived class must override.</value>

src/libraries/System.Security.Cryptography.Primitives/src/System/Security/Cryptography/SymmetricAlgorithm.cs

@@ -490,8 +490,8 @@ public byte[] DecryptEcb(ReadOnlySpan<byte> ciphertext, PaddingMode paddingMode)
 
             // Array.Resize will no-op if the array does not need to be resized.
             Array.Resize(ref decryptBuffer, written);
-                return decryptBuffer;
-            }
+            return decryptBuffer;
+        }
 
         /// <summary>
         ///   Decrypts data into the specified buffer, using ECB mode with the specified padding mode.
@@ -598,21 +598,15 @@ public byte[] EncryptEcb(ReadOnlySpan<byte> plaintext, PaddingMode paddingMode)
             // We expect most if not all uses to encrypt to exactly the ciphertextLength
             byte[] buffer = GC.AllocateUninitializedArray<byte>(ciphertextLength);
 
-            if (!TryEncryptEcbCore(plaintext, buffer, paddingMode, out int written))
+            if (!TryEncryptEcbCore(plaintext, buffer, paddingMode, out int written) ||
+                written != ciphertextLength)
             {
-                // This means a user-derived imiplementation added more padding than we expected.
-                throw new CryptographicException(SR.Argument_DestinationTooShort);
-            }
-
-            if (written != ciphertextLength)
-            {
-                // This should not happen, but could if a derived class's implementation of core
+                // This means a user-derived imiplementation added more padding than we expected or
                 // did something non-standard (encrypt to a partial block). This can't happen for
                 // multiple padding blocks since the buffer would have been too small in the first
                 // place. It doesn't make sense to try and support partial block encryption, likely
                 // something went very wrong. So throw.
-
-                throw new CryptographicException(SR.Cryptography_EncryptedIncorrectPadding);
+                throw new CryptographicException(SR.Format(SR.Cryptography_EncryptedIncorrectLength, nameof(TryEncryptEcbCore)));
             }
 
             return buffer;