implement OuterEncryptionReader

src/KeyKeeper/PasswordStore/Crypto/OuterEncryptionReader.cs

@@ -0,0 +1,200 @@
+using System;
+using System.IO;
+using System.Security.Cryptography;
+
+namespace KeyKeeper.PasswordStore.Crypto;
+
+public class OuterEncryptionReader : Stream
+{
+    public override bool CanRead => true;
+    public override bool CanWrite => false;
+    public override bool CanSeek => false;
+    public override bool CanTimeout => false;
+    public override int ReadTimeout
+    {
+        get { throw new InvalidOperationException(); }
+        set { throw new InvalidOperationException(); }
+    }
+    public override int WriteTimeout
+    {
+        get { throw new InvalidOperationException(); }
+        set { throw new InvalidOperationException(); }
+    }
+    public override long Position
+    {
+        get => position;
+        set => position = value;
+    }
+    public override long Length => throw new NotSupportedException();
+
+    private FileStream file;
+    private byte[] key;
+    private Aes aes;
+    private ICryptoTransform decryptor;
+
+    /// <summary>
+    /// Последний считанный из файла расшифрованный чанк. Первые
+    /// <see cref="chunkPosition"/> байт - уже отданные при вызовах Read,
+    /// остальные - еще не отданные.    
+    /// </summary>
+    private byte[]? currentChunk;
+    private int chunkPosition = 0;
+    /// <summary>
+    /// Порядковый номер чанка, лежащего в <see cref="currentChunk"/>. 
+    /// </summary>
+    private int currentChunkOrdinal = 0;
+    private bool isCurrentChunkLast;
+    private long position = 0;
+
+    /// <summary>
+    /// Ещё не расшифрованные байты, которые были считаны из файла, но их
+    /// оказалось меньше, чем вмещает блок AES (менее 16 байт).
+    /// </summary>
+    private byte[] encryptedRemainder;
+    /// <summary>
+    /// Количество полезных байт в <see cref="encryptedRemainder"/>. 
+    /// </summary>
+    private int encryptedRemainderLength;
+
+    /// <summary>
+    /// Создаёт экземпляр reader, использующий файловый поток для чтения.
+    /// </summary>
+    /// <param name="file">Файловый поток, указатель которого должен стоять на
+    /// первом content chunk.</param>
+    /// <param name="key">Ключ, который будет использован для проверки HMAC
+    /// и расшифровки содержимого.</param>
+    public OuterEncryptionReader(FileStream file, byte[] key, byte[] iv)
+    {
+        aes = Aes.Create();
+        aes.KeySize = 256;
+        aes.Key = key;
+        aes.IV = iv;
+        aes.Mode = CipherMode.CFB;
+        aes.Padding = PaddingMode.None;
+        decryptor = aes.CreateDecryptor();
+
+        this.file = file;
+        this.key = key;
+        currentChunk = null;
+        encryptedRemainder = new byte[16];
+        encryptedRemainderLength = 0;
+        LoadAndDecryptNextChunk();
+    }
+
+    public override void SetLength(long value)
+        => throw new NotSupportedException();
+
+    public override IAsyncResult BeginRead(byte[] buffer, int offset, int count,
+                                           AsyncCallback? callback, object? state)
+        => throw new NotSupportedException();
+    public override IAsyncResult BeginWrite(byte[] buffer, int offset, int count,
+                                            AsyncCallback? callback, object? state)
+        => throw new NotSupportedException();
+
+    public override void Flush()
+    {}
+
+    public override int EndRead(IAsyncResult asyncResult)
+        => throw new NotSupportedException();
+    public override void EndWrite(IAsyncResult asyncResult)
+        => throw new NotSupportedException();
+
+
+    public override long Seek(long offset, SeekOrigin origin)
+        => throw new NotSupportedException();
+
+    public override int Read(byte[] buffer, int offset, int count)
+        => Read(new Span<byte>(buffer, offset, count));
+
+    public override void Write(byte[] buffer, int offset, int count)
+        => throw new NotSupportedException();
+    public override void Write(ReadOnlySpan<byte> buffer)
+        => throw new NotSupportedException();
+
+    public override int Read(Span<byte> buffer)
+    {
+        Console.WriteLine("OE read " + buffer.Length);
+        int toRead = buffer.Length;
+        int read = 0;
+        while (toRead > 0)
+        {
+            if (currentChunk == null || currentChunk.Length - chunkPosition == 0)
+            {
+                if (!isCurrentChunkLast)
+                {
+                    Console.WriteLine("OER: reading next chunk");
+                    LoadAndDecryptNextChunk();
+                }
+                else
+                {
+                    Console.WriteLine("OER: read " + read + " bytes before EOF");
+                    break;
+                }
+            }
+            byte[] chunk = currentChunk!;
+            int n = Math.Min(toRead, chunk.Length - chunkPosition);
+            Console.WriteLine("OER: copy " + n + " bytes chunk+" + chunkPosition + " -> buffer+" + read);
+            new Span<byte>(chunk, chunkPosition, n).CopyTo(buffer.Slice(read));
+            read += n;
+            toRead -= n;
+            chunkPosition += n;
+            position += n;
+            Console.WriteLine(string.Format("read={} toread={} pos={}", read, toRead, chunkPosition));
+        }
+        return read;
+    }
+
+    private void LoadAndDecryptNextChunk()
+    {
+        if (isCurrentChunkLast)
+            return;
+        var chunk = PassStoreContentChunk.GetFromStream(file, key, currentChunkOrdinal);
+        isCurrentChunkLast = chunk.IsLast;
+        var encryptedData = chunk.GetContent();
+        EraseCurrentChunk();
+
+        int decrypted = 0, read = 0;
+        currentChunk = new byte[(encryptedData.Length + encryptedRemainderLength) / 16 * 16];
+        if (encryptedRemainderLength > 0 && encryptedData.Length >= 16 - encryptedRemainderLength)
+        {
+            encryptedData.Slice(0, 16 - encryptedRemainderLength)
+                    .CopyTo(new Span<byte>(encryptedRemainder, encryptedRemainderLength, 16 - encryptedRemainderLength));
+            decryptor.TransformBlock(encryptedRemainder, 0, 16, currentChunk, 0);
+            decrypted = 16;
+            read = 16 - encryptedRemainderLength;
+            encryptedRemainderLength = 0;
+        }
+        if (!isCurrentChunkLast)
+        {
+            int wholeBlocksLen = (encryptedData.Length - decrypted) / 16 * 16;
+            if (wholeBlocksLen > 0)
+            {
+                byte[] blocks = new byte[wholeBlocksLen];
+                encryptedData.Slice(read, wholeBlocksLen).CopyTo(blocks);
+                decryptor.TransformBlock(blocks, 0, wholeBlocksLen, currentChunk, decrypted);
+                decrypted += wholeBlocksLen;
+                read += wholeBlocksLen;
+            }
+            if (read < encryptedData.Length)
+            {
+                encryptedRemainderLength = encryptedData.Length - read;
+                encryptedData.Slice(read, encryptedRemainderLength).CopyTo(encryptedRemainder);
+            }
+        } else
+        {
+            byte[] finalData = new byte[encryptedData.Length - read];
+            encryptedData.Slice(read).CopyTo(finalData);
+            byte[] decryptedFinalData = decryptor.TransformFinalBlock(finalData, 0, finalData.Length);
+            decryptedFinalData.CopyTo(currentChunk, decrypted);
+            Array.Fill<byte>(decryptedFinalData, 0);
+        }
+        chunkPosition = 0;
+    }
+
+    private void EraseCurrentChunk()
+    {
+        if (currentChunk == null) return;
+        Array.Fill<byte>(currentChunk, 0);
+        currentChunk = null;
+    }
+}