/// <summary>
        /// Starts an explicit decryption context.
        /// </summary>
        /// <param name="buffer">The buffer.</param>
        /// <returns>A encryption context</returns>
        public CryptContext StartExplicitDecryptionContext(byte[] buffer)
        {
            ContextSafeHandle handle = Library.mongocrypt_ctx_new(_handle);

            unsafe
            {
                fixed(byte *p = buffer)
                {
                    IntPtr ptr = (IntPtr)p;

                    using (PinnedBinary pinned = new PinnedBinary(ptr, (uint)buffer.Length))
                    {
                        // Let mongocrypt run strlen
                        handle.Check(_status, Library.mongocrypt_ctx_explicit_decrypt_init(handle, pinned.Handle));
                    }
                }
            }

            return(new CryptContext(handle));
        }