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diff --git a/Userland/Libraries/LibCrypto/Cipher/Mode/Mode.h b/Userland/Libraries/LibCrypto/Cipher/Mode/Mode.h
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+++ b/Userland/Libraries/LibCrypto/Cipher/Mode/Mode.h
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+/*
+ * Copyright (c) 2020, Ali Mohammad Pur <ali.mpfard@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/ByteBuffer.h>
+#include <AK/Span.h>
+#include <AK/StdLibExtras.h>
+#include <LibCrypto/Cipher/Cipher.h>
+
+namespace Crypto {
+namespace Cipher {
+
+template<typename T>
+class Mode {
+public:
+    virtual ~Mode() { }
+
+    virtual void encrypt(ReadonlyBytes in, Bytes& out, ReadonlyBytes ivec = {}, Bytes* ivec_out = nullptr) = 0;
+    virtual void decrypt(ReadonlyBytes in, Bytes& out, ReadonlyBytes ivec = {}) = 0;
+
+    virtual size_t IV_length() const = 0;
+
+    const T& cipher() const { return m_cipher; }
+
+    ByteBuffer create_aligned_buffer(size_t input_size) const
+    {
+        size_t remainder = (input_size + T::block_size()) % T::block_size();
+        if (remainder == 0)
+            return ByteBuffer::create_uninitialized(input_size);
+        else
+            return ByteBuffer::create_uninitialized(input_size + T::block_size() - remainder);
+    }
+
+    virtual String class_name() const = 0;
+    T& cipher() { return m_cipher; }
+
+protected:
+    virtual void prune_padding(Bytes& data)
+    {
+        auto size = data.size();
+        switch (m_cipher.padding_mode()) {
+        case PaddingMode::CMS: {
+            auto maybe_padding_length = data[size - 1];
+            if (maybe_padding_length >= T::block_size()) {
+                // cannot be padding (the entire block cannot be padding)
+                return;
+            }
+            for (auto i = size - maybe_padding_length; i < size; ++i) {
+                if (data[i] != maybe_padding_length) {
+                    // not padding, part of data
+                    return;
+                }
+            }
+            data = data.slice(0, size - maybe_padding_length);
+            break;
+        }
+        case PaddingMode::RFC5246: {
+            auto maybe_padding_length = data[size - 1];
+            // FIXME: If we want constant-time operations, this loop should not stop
+            for (auto i = size - maybe_padding_length - 1; i < size; ++i) {
+                if (data[i] != maybe_padding_length) {
+                    // note that this is likely invalid padding
+                    return;
+                }
+            }
+            data = data.slice(0, size - maybe_padding_length - 1);
+            break;
+        }
+        case PaddingMode::Null: {
+            while (data[size - 1] == 0)
+                --size;
+            data = data.slice(0, size);
+            break;
+        }
+        default:
+            // FIXME: support other padding modes
+            ASSERT_NOT_REACHED();
+            break;
+        }
+    }
+
+    // FIXME: Somehow add a reference version of this
+    template<typename... Args>
+    Mode(Args... args)
+        : m_cipher(args...)
+    {
+    }
+
+private:
+    T m_cipher;
+};
+}
+
+}