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Basic formatting applied. Unnecessary comments have been removed. Suspicious code is covered by TODO.

Hcs.Client/GostCryptography/Native/SafeProvHandleImpl.cs

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+using Microsoft.Win32.SafeHandles;
+using System;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+using System.Security;
+
+namespace GostCryptography.Native
+{
+    /// <summary>
+    /// Дескриптор криптографического провайдера
+    /// </summary>
+    [SecurityCritical]
+    public sealed class SafeProvHandleImpl : SafeHandleZeroOrMinusOneIsInvalid
+    {
+        public static SafeProvHandleImpl InvalidHandle => new SafeProvHandleImpl(IntPtr.Zero);
+
+        public SafeProvHandleImpl() : base(true)
+        {
+        }
+
+        public SafeProvHandleImpl(IntPtr handle) : base(true)
+        {
+            SetHandle(handle);
+        }
+
+        public SafeProvHandleImpl(IntPtr handle, bool addref) : base(true)
+        {
+            if (!addref)
+            {
+                SetHandle(handle);
+            }
+            else
+            {
+                bool success;
+                int errorCode;
+
+                // Обеспечивает атомарность блока finally
+                RuntimeHelpers.PrepareConstrainedRegions();
+
+                try { }
+                finally
+                {
+                    success = CryptoApi.CryptContextAddRef(handle, null, 0);
+                    errorCode = Marshal.GetLastWin32Error();
+
+                    if (success)
+                    {
+                        SetHandle(handle);
+                    }
+                }
+
+                if (!success)
+                {
+                    throw ExceptionUtility.CryptographicException(errorCode);
+                }
+            }
+        }
+
+        public bool DeleteOnClose { get; set; }
+
+        [SecurityCritical]
+        protected override bool ReleaseHandle()
+        {
+            if (DeleteOnClose)
+            {
+                CryptoApi.CryptSetProvParam2(handle, Constants.PP_DELETE_KEYSET, null, 0);
+            }
+            else
+            {
+                CryptoApi.CryptReleaseContext(handle, 0);
+            }
+
+            return true;
+        }
+    }
+}