diff --git a/src/KeyKeeper/PasswordStore/Crypto/CompositeKey.cs b/src/KeyKeeper/PasswordStore/Crypto/CompositeKey.cs
new file mode 100644
index 0000000..f95b90e
--- /dev/null
+++ b/src/KeyKeeper/PasswordStore/Crypto/CompositeKey.cs
@@ -0,0 +1,51 @@
+using System;
+using System.Security.Cryptography;
+using System.Text;
+
+namespace KeyKeeper.PasswordStore.Crypto;
+
+public class CompositeKey
+{
+    public string Password { get; }
+    public byte[]? Salt
+    {
+        get { return salt; }
+        set
+        {
+            if (salt == null)
+                salt = value;
+        }
+    }
+
+    private byte[]? salt;
+
+    public bool CanComputeHash
+    {
+        get { return salt != null; }
+    }
+
+    public CompositeKey(string password, byte[]? salt)
+    {
+        if (password == null)
+            throw new ArgumentNullException("password");
+        Password = password;
+
+        if (salt != null && (salt.Length < FileFormatConstants.MIN_MASTER_SALT_LEN ||
+            salt.Length > FileFormatConstants.MAX_MASTER_SALT_LEN))
+            throw new ArgumentException("salt");
+        this.salt = salt;
+    }
+
+    public byte[] Hash()
+    {
+        if (!CanComputeHash)
+            throw new InvalidOperationException("salt is not set");
+        byte[] passwordBytes = Encoding.UTF8.GetBytes(Password);
+        byte[] hashedString = new byte[passwordBytes.Length + Salt.Length * 2];
+        Salt.CopyTo(hashedString, 0);
+        passwordBytes.CopyTo(hashedString, Salt.Length);
+        Salt.CopyTo(hashedString, Salt.Length + passwordBytes.Length);
+
+        return SHA256.HashData(hashedString);
+    }
+}
diff --git a/src/KeyKeeper/PasswordStore/Crypto/KeyDerivation/AesKdf.cs b/src/KeyKeeper/PasswordStore/Crypto/KeyDerivation/AesKdf.cs
new file mode 100644
index 0000000..1231fb0
--- /dev/null
+++ b/src/KeyKeeper/PasswordStore/Crypto/KeyDerivation/AesKdf.cs
@@ -0,0 +1,42 @@
+using System;
+using System.Security.Cryptography;
+
+namespace KeyKeeper.PasswordStore.Crypto.KeyDerivation;
+
+public class AesKdf : MasterKeyDerivationFunction
+{
+    public const int MIN_ROUNDS = 10;
+    public const int MAX_ROUNDS = 25_000_000;
+    public const int SEED_LENGTH = 32;
+
+    private int rounds;
+    private byte[] seed;
+
+    public AesKdf(int rounds, byte[] seed)
+    {
+        if (rounds < MIN_ROUNDS || rounds > MAX_ROUNDS)
+            throw new ArgumentOutOfRangeException(nameof(rounds));
+        if (seed.Length != SEED_LENGTH)
+            throw new ArgumentException("seed length must be " + SEED_LENGTH);
+        this.rounds = rounds;
+        this.seed = seed;
+    }
+
+    public override byte[] Derive(CompositeKey source, int keySizeBytes)
+    {
+        if (keySizeBytes > SEED_LENGTH)
+            throw new ArgumentOutOfRangeException(nameof(keySizeBytes));
+
+        byte[] key = source.Hash()[..SEED_LENGTH];
+        byte[] nextKey = new byte[SEED_LENGTH];
+        Aes cipher = Aes.Create();
+        cipher.KeySize = SEED_LENGTH * 8;
+        for (int i = 0; i < rounds; ++i)
+        {
+            cipher.Key = key;
+            cipher.EncryptEcb(seed, nextKey, PaddingMode.None);
+            (nextKey, key) = (key, nextKey);
+        }
+        return key;
+    }
+}
diff --git a/src/KeyKeeper/PasswordStore/Crypto/KeyDerivation/MasterKeyDerivationFunction.cs b/src/KeyKeeper/PasswordStore/Crypto/KeyDerivation/MasterKeyDerivationFunction.cs
new file mode 100644
index 0000000..6118e25
--- /dev/null
+++ b/src/KeyKeeper/PasswordStore/Crypto/KeyDerivation/MasterKeyDerivationFunction.cs
@@ -0,0 +1,6 @@
+namespace KeyKeeper.PasswordStore.Crypto;
+
+public abstract class MasterKeyDerivationFunction
+{
+    public abstract byte[] Derive(CompositeKey source, int keySizeBytes);
+}
diff --git a/src/KeyKeeper/PasswordStore/Crypto/OuterEncryptionReader.cs b/src/KeyKeeper/PasswordStore/Crypto/OuterEncryptionReader.cs
new file mode 100644
index 0000000..035215b
--- /dev/null
+++ b/src/KeyKeeper/PasswordStore/Crypto/OuterEncryptionReader.cs
@@ -0,0 +1,204 @@
+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 { throw new NotSupportedException(); }
+    }
+    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 nextChunkOrdinal = 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={0} toread={1} pos={2}", read, toRead, chunkPosition));
+        }
+        return read;
+    }
+
+    private void LoadAndDecryptNextChunk()
+    {
+        if (isCurrentChunkLast)
+            return;
+        var chunk = PassStoreContentChunk.GetFromStream(file, key, nextChunkOrdinal);
+        nextChunkOrdinal += 1;
+        isCurrentChunkLast = chunk.IsLast;
+        var encryptedData = chunk.GetContent();
+        EraseCurrentChunk();
+
+        int decrypted = 0, read = 0;
+        if (isCurrentChunkLast)
+            currentChunk = new byte[encryptedData.Length + encryptedRemainderLength];
+        else
+            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;
+    }
+}
diff --git a/src/KeyKeeper/PasswordStore/Crypto/OuterEncryptionUtil.cs b/src/KeyKeeper/PasswordStore/Crypto/OuterEncryptionUtil.cs
new file mode 100644
index 0000000..8708517
--- /dev/null
+++ b/src/KeyKeeper/PasswordStore/Crypto/OuterEncryptionUtil.cs
@@ -0,0 +1,70 @@
+using System;
+using System.IO;
+using static KeyKeeper.PasswordStore.FileFormatConstants;
+
+namespace KeyKeeper.PasswordStore.Crypto;
+
+public static class OuterEncryptionUtil
+{
+    /// <summary>
+    /// Проверяет корректность заголовка внешнего шифрования,
+    /// который содержит соль для мастер-ключа и параметры шифрования +
+    /// генерации ключа. Сдвигает указатель потока f на первый байт после
+    /// заголовка.
+    /// </summary>
+    /// <param name="f">Поток, указатель которого стоит на начале заголовка
+    /// внешнего шифрования.</param>
+    /// <exception cref="PassStoreFileException">Если заголовок содержит некорректные поля или неполный</exception>
+    public static void CheckOuterEncryptionHeader(FileStream f)
+    {
+        BinaryReader rd = new(f);
+        try
+        {
+            byte masterSaltLen = rd.ReadByte();
+
+            if (masterSaltLen < MIN_MASTER_SALT_LEN || masterSaltLen > MAX_MASTER_SALT_LEN)
+            {
+                throw PassStoreFileException.InvalidCryptoHeader;
+            }
+
+            f.Seek(masterSaltLen, SeekOrigin.Current);
+
+            byte encryptAlgo = rd.ReadByte();
+
+            if (encryptAlgo == ENCRYPT_ALGO_AES)
+            {
+                // пропустить 16 байт вектора инициализации AES
+                f.Seek(16, SeekOrigin.Current);
+            }
+            else
+            {
+                throw PassStoreFileException.InvalidCryptoHeader;
+            }
+
+            byte keyDerivationFunctionType = rd.ReadByte();
+
+            if (keyDerivationFunctionType == KDF_TYPE_AESKDF)
+            {
+                int nRounds;
+                try
+                {
+                    nRounds = rd.Read7BitEncodedInt();
+                }
+                catch (FormatException)
+                {
+                    throw PassStoreFileException.InvalidCryptoHeader;
+                }
+                if (nRounds < MIN_AESKDF_ROUNDS || nRounds > MAX_AESKDF_ROUNDS)
+                {
+                    throw PassStoreFileException.InvalidCryptoHeader;
+                }
+                // пропустить 32 байта сида AES-KDF
+                f.Seek(32, SeekOrigin.Current);
+            }
+        }
+        catch (EndOfStreamException)
+        {
+            throw PassStoreFileException.UnexpectedEndOfFile;
+        }
+    }
+}
diff --git a/src/KeyKeeper/PasswordStore/Crypto/OuterEncryptionWriter.cs b/src/KeyKeeper/PasswordStore/Crypto/OuterEncryptionWriter.cs
new file mode 100644
index 0000000..1357acd
--- /dev/null
+++ b/src/KeyKeeper/PasswordStore/Crypto/OuterEncryptionWriter.cs
@@ -0,0 +1,131 @@
+using System;
+using System.IO;
+using System.Security.Cryptography;
+
+namespace KeyKeeper.PasswordStore.Crypto;
+
+public class OuterEncryptionWriter : Stream
+{
+    public override bool CanRead => false;
+    public override bool CanWrite => true;
+    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 { throw new NotSupportedException(); }
+    }
+    public override long Length => throw new NotSupportedException();
+
+    private FileStream file;
+    private byte[] key;
+    private Aes aes;
+    private ICryptoTransform encryptor;
+
+    private byte[] currentChunk;
+    private int currentChunkOrdinal = 0;
+    private int chunkPosition = 0;
+    private long position = 0;
+
+    public OuterEncryptionWriter(FileStream file, byte[] key, byte[] iv)
+    {
+        if (!file.CanWrite)
+            throw new ArgumentException("file must be writeable");
+        this.file = file;
+        this.key = key;
+
+        currentChunk = new byte[524288];
+
+        aes = Aes.Create();
+        aes.KeySize = 256;
+        aes.Key = key;
+        aes.IV = iv;
+        aes.Mode = CipherMode.CFB;
+        aes.Padding = PaddingMode.None;
+        encryptor = aes.CreateEncryptor();
+    }
+
+    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 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(Span<byte> buffer)
+        => throw new NotSupportedException();
+
+    public override int Read(byte[] buffer, int offset, int count)
+        => throw new NotImplementedException();
+
+    public override void Write(byte[] buffer, int offset, int count)
+        => Write(new ReadOnlySpan<byte>(buffer, offset, count));
+
+    public override void Write(ReadOnlySpan<byte> buffer)
+    {
+        int written = 0;
+        while (written < buffer.Length)
+        {
+            if (chunkPosition == currentChunk.Length)
+                EncryptAndStoreCurrentFullChunk();
+            int n = Math.Min(buffer.Length, currentChunk.Length - chunkPosition);
+            buffer.Slice(written, n).CopyTo(new Span<byte>(currentChunk, chunkPosition, n));
+            written += n;
+            chunkPosition += n;
+            position += n;
+        }
+    }
+
+    /// <summary>
+    /// Шифрует оставшиеся данные и добавляет к файлу чанк с пометкой о том
+    /// что он последний. Вызов после завершения записи полезных данных
+    /// обязателен, в противном случае потеря данных неизбежна.
+    /// </summary>
+    public override void Flush()
+    {
+        byte[] encryptedData = encryptor.TransformFinalBlock(currentChunk, 0, chunkPosition);
+        PassStoreContentChunk chunk = PassStoreContentChunk.FromEncryptedContent(encryptedData, key, currentChunkOrdinal, true);
+        file.Write(chunk.Chunk);
+        EraseCurrentChunk();
+        chunkPosition = 0;
+    }
+
+    private void EncryptAndStoreCurrentFullChunk()
+    {
+        byte[] encryptedData = new byte[currentChunk.Length];
+        encryptor.TransformBlock(currentChunk, 0, currentChunk.Length, encryptedData, 0);
+        PassStoreContentChunk chunk = PassStoreContentChunk.FromEncryptedContent(encryptedData, key, currentChunkOrdinal, false);
+        currentChunkOrdinal += 1;
+        file.Write(chunk.Chunk);
+        EraseCurrentChunk();
+        chunkPosition = 0;
+    }
+
+    private void EraseCurrentChunk()
+    {
+        if (currentChunk == null) return;
+        Array.Fill<byte>(currentChunk, 0);
+    }
+}
\ No newline at end of file
diff --git a/src/KeyKeeper/PasswordStore/Crypto/PassStoreContentChunk.cs b/src/KeyKeeper/PasswordStore/Crypto/PassStoreContentChunk.cs
new file mode 100644
index 0000000..30efa6d
--- /dev/null
+++ b/src/KeyKeeper/PasswordStore/Crypto/PassStoreContentChunk.cs
@@ -0,0 +1,156 @@
+using System;
+using System.Linq;
+using System.Buffers.Binary;
+using System.IO;
+using System.Security.Cryptography;
+using static KeyKeeper.PasswordStore.FileFormatConstants;
+
+namespace KeyKeeper.PasswordStore.Crypto;
+
+/// <summary>
+/// Класс, представляющий собой обертку над content chunkом, считанным из файла
+/// хранилища. Не расшифровывает содержимое, но проверяет целостность и
+/// подлинность при создании объекта.
+/// </summary>
+public class PassStoreContentChunk
+{
+    public bool IsLast { get; }
+    public byte[] Chunk { get { return chunk; } }
+
+    private byte[] chunk;
+    private int chunkLen;
+
+    /// <summary>
+    /// Создаёт объект content chunk, считывая массив байт. Бросает исключение
+    /// в случае, если массив не содержит корректный content chunk или не
+    /// совпадает HMAC
+    /// </summary>
+    /// <param name="chunk">Массив байт, содержащий весь content chunk, включая
+    /// длину и HMAC</param>
+    /// <param name="key">Ключ от хранилища. Используется только для
+    /// проверки HMAC и не хранится в объекте</param>
+    /// <param name="chunkOrdinal">Порядковый номер content chunk'а, начиная
+    /// с 0</param>
+    public PassStoreContentChunk(byte[] chunk, byte[] key, int chunkOrdinal)
+    {
+        this.chunk = chunk;
+
+        MemoryStream str = new(chunk);
+        BinaryReader rd = new(str);
+
+        try
+        {
+            byte[] chunkLenBytes = new byte[3];
+            if (str.Read(chunkLenBytes) < 3)
+                throw PassStoreFileException.UnexpectedEndOfFile;
+            chunkLen = BinaryPrimitives.ReadUInt16LittleEndian(new(chunkLenBytes, 0, 2));
+            chunkLen |= chunkLenBytes[2] << 16;
+        }
+        catch (EndOfStreamException)
+        {
+            throw PassStoreFileException.UnexpectedEndOfFile;
+        }
+
+        IsLast = (chunkLen & (1 << 23)) != 0;
+        chunkLen &= ~(1 << 23);
+
+        if (chunk.Length != chunkLen + 3 + HMAC_SIZE)
+        {
+            throw PassStoreFileException.UnexpectedEndOfFile;
+        }
+
+        byte[] storedHmac = new byte[HMAC_SIZE];
+        str.Read(storedHmac, 0, HMAC_SIZE);
+
+        byte[] dataToHash = chunk[(int)str.Position..];
+        byte[] actualHmac = ComputeHmac(dataToHash, key, chunkOrdinal);
+        
+        if (!storedHmac.SequenceEqual(actualHmac))
+        {
+            throw PassStoreFileException.ContentHMACMismatch;
+        }
+    }
+
+    private PassStoreContentChunk(byte[] chunk, bool isLast)
+    {
+        this.chunk = chunk;
+        this.chunkLen = chunk.Length;
+        this.IsLast = isLast;
+    }
+
+    /// <summary>
+    /// Создаёт объект content chunk, считывая байты из потока. Бросает
+    /// исключение в случае, если массив не содержит корректный content chunk
+    /// или не совпадает HMAC
+    /// </summary>
+    /// <param name="chunk">Массив байт, содержащий весь content chunk, включая
+    /// длину и HMAC</param>
+    /// <param name="key">Ключ от хранилища. Используется только для
+    /// проверки HMAC и не хранится в объекте</param>
+    /// <param name="chunkOrdinal">Порядковый номер content chunk'а, начиная
+    /// с 0</param>
+    public static PassStoreContentChunk GetFromStream(Stream s, byte[] key, int chunkOrdinal)
+    {
+        BinaryReader rd = new(s);
+        int chunkLen;
+
+        byte[] chunkLenBytes = new byte[3];
+        if (s.Read(chunkLenBytes) < 3)
+            throw PassStoreFileException.UnexpectedEndOfFile;
+        chunkLen = BinaryPrimitives.ReadUInt16LittleEndian(new(chunkLenBytes, 0, 2));
+        chunkLen |= chunkLenBytes[2] << 16;
+
+        chunkLen &= ~(1 << 23); // 23 бит имеет специальное значение
+        byte[] chunk = new byte[3 + HMAC_SIZE + chunkLen];
+        Array.Copy(chunkLenBytes, chunk, 3);
+        if (s.Read(chunk, 3, HMAC_SIZE + chunkLen) < HMAC_SIZE + chunkLen)
+        {
+            throw PassStoreFileException.UnexpectedEndOfFile;
+        }
+        return new PassStoreContentChunk(chunk, key, chunkOrdinal);
+    }
+
+    public static PassStoreContentChunk FromEncryptedContent(byte[] content, byte[] key, int chunkOrdinal, bool isLast)
+    {
+        int chunkLen = content.Length;
+        byte[] chunk = new byte[chunkLen + HMAC_SIZE + 3];
+        BinaryPrimitives.WriteUInt16LittleEndian(new Span<byte>(chunk, 0, 2), (ushort)(chunkLen & 0xffff));
+        chunk[2] = (byte)(chunkLen >> 16);
+        if (isLast) chunk[2] |= 1 << 7;
+        ComputeHmac(content, key, chunkOrdinal).CopyTo(chunk, 3);
+        content.CopyTo(chunk, 3 + HMAC_SIZE);
+        return new PassStoreContentChunk(chunk, isLast);
+    }
+
+    public ReadOnlySpan<byte> GetContent()
+    {
+        return new ReadOnlySpan<byte>(chunk, 3 + HMAC_SIZE, chunkLen);
+    }
+
+    private static byte[] ComputeHmac(byte[] data, byte[] key, int chunkOrdinal)
+    {
+        SHA3_512 hasher = SHA3_512.Create();
+        byte[] innerKey = key.Select(x => (byte)(x ^ 0x36)).ToArray();
+        byte[] outerKey = key.Select(x => (byte)(x ^ 0x5c)).ToArray();
+
+        hasher.TransformBlock(innerKey, 0, innerKey.Length, null, 0);
+        Array.Fill<byte>(innerKey, 0); // erase key after use
+
+        hasher.TransformBlock(data, 0, data.Length, null, 0);
+
+        byte[] encodedOrdinal = new byte[sizeof(int)];
+        BinaryPrimitives.WriteInt32LittleEndian(new Span<byte>(encodedOrdinal), chunkOrdinal);
+
+        hasher.TransformFinalBlock(encodedOrdinal, 0, encodedOrdinal.Length);
+        byte[] innerHash = hasher.Hash!;
+        hasher.Clear();
+
+        hasher = SHA3_512.Create();
+        hasher.TransformBlock(outerKey, 0, outerKey.Length, null, 0);
+        Array.Fill<byte>(outerKey, 0);
+        hasher.TransformFinalBlock(innerHash, 0, innerHash.Length);
+        byte[] hmac = hasher.Hash!;
+        hasher.Clear();
+        return hmac;
+    }
+}
diff --git a/src/KeyKeeper/PasswordStore/FileFormatConstants.cs b/src/KeyKeeper/PasswordStore/FileFormatConstants.cs
new file mode 100644
index 0000000..761f5a0
--- /dev/null
+++ b/src/KeyKeeper/PasswordStore/FileFormatConstants.cs
@@ -0,0 +1,34 @@
+using System.Security.Cryptography;
+using KeyKeeper.PasswordStore.Crypto.KeyDerivation;
+
+namespace KeyKeeper.PasswordStore;
+
+static class FileFormatConstants
+{
+    public const int MIN_MASTER_SALT_LEN = 8;
+    public const int MAX_MASTER_SALT_LEN = 40;
+    public const int MIN_AESKDF_ROUNDS = AesKdf.MIN_ROUNDS;
+    public const int MAX_AESKDF_ROUNDS = AesKdf.MAX_ROUNDS;
+    public const byte ENCRYPT_ALGO_AES = 14;
+    public const byte KDF_TYPE_AESKDF = 195;
+    public const int HMAC_SIZE = HMACSHA3_512.HashSizeInBytes;
+    public const uint FILE_FIELD_BEGIN = 0x7853dbd5;
+    public const uint FILE_FIELD_INNER_CRYPTO = 0x613e91e4;
+    public const uint FILE_FIELD_CONFIG = 0xd36a53c0;
+    public const uint FILE_FIELD_STORE = 0x981f9bc8;
+    public const uint FILE_FIELD_END = 0x010ba81a;
+    public const byte ENTRY_PASS_ID = 0x00;
+    public const byte ENTRY_GROUP_ID = 0x01;
+    public const byte LOGIN_FIELD_PASSWORD_ID = 0x00;
+    public const byte LOGIN_FIELD_USERNAME_ID = 0x01;
+    public const byte LOGIN_FIELD_EMAIL_ID = 0x02;
+    public const byte LOGIN_FIELD_ACCOUNT_NUMBER_ID = 0x03;
+    public const byte LOGIN_FIELD_NOTES_ID = 0x04;
+    public const byte LOGIN_FIELD_CUSTOM_ID = 0xff; // пока не используется
+    public const byte GROUP_TYPE_ROOT = 0x00;
+    public const byte GROUP_TYPE_DEFAULT = 0x01;
+    public const byte GROUP_TYPE_FAVOURITES = 0x02;
+    public const byte GROUP_TYPE_SIMPLE = 0x03;
+    public const byte GROUP_TYPE_CUSTOM = 0xff; // пока не используется
+    public static readonly byte[] BEGIN_MARKER = [0x5f, 0x4f, 0xcf, 0x67, 0xc0, 0x90, 0xd0, 0xe5];
+}
\ No newline at end of file
diff --git a/src/KeyKeeper/PasswordStore/FileFormatUtil.cs b/src/KeyKeeper/PasswordStore/FileFormatUtil.cs
new file mode 100644
index 0000000..18ce17c
--- /dev/null
+++ b/src/KeyKeeper/PasswordStore/FileFormatUtil.cs
@@ -0,0 +1,80 @@
+using System;
+using System.Buffers.Binary;
+using System.IO;
+using System.Text;
+
+namespace KeyKeeper.PasswordStore;
+
+static class FileFormatUtil
+{
+    public static int WriteVarUint16(Stream str, ulong number)
+    {
+        int size = 0;
+        do {
+            ushort portion = (ushort)(number & 0x7fff);
+            number >>= 15;
+            if (number != 0)
+                portion |= 1 << 15;
+            size += 2;
+            str.WriteByte((byte)(portion & 0xff));
+            str.WriteByte((byte)(portion >> 8));
+        }
+        while (number != 0);
+        return size;
+    }
+
+    public static ulong ReadVarUint16(Stream str)
+    {
+        ulong number = 0;
+        int i = 0;
+        while (true)
+        {
+            int b = str.ReadByte();
+            if (b == -1)
+                throw PassStoreFileException.UnexpectedEndOfFile;
+            number |= (ulong)b << i;
+            i += 8;
+            b = str.ReadByte();
+            if (b == -1)
+                throw PassStoreFileException.UnexpectedEndOfFile;
+            number |= (ulong)(b & 0x7f) << i;
+            if ((b & 0x80) == 0)
+                break;
+            i += 7;
+        }
+        return number;
+    }
+
+    public static int WriteU8TaggedString(Stream str, string s)
+    {
+        byte[] b = Encoding.UTF8.GetBytes(s);
+        if (b.Length > 255)
+            throw new ArgumentException("string too long");
+        str.WriteByte((byte)b.Length);
+        str.Write(b);
+        return b.Length + 1;
+    }
+
+    public static int WriteU16TaggedString(Stream str, string s)
+    {
+        byte[] b = Encoding.UTF8.GetBytes(s);
+        if (b.Length > 65535)
+            throw new ArgumentException("string too long");
+        str.WriteByte((byte)(b.Length & 0xff));
+        str.WriteByte((byte)(b.Length >> 8));
+        str.Write(b);
+        return b.Length + 2;
+    }
+
+    public static string ReadU16TaggedString(Stream str)
+    {
+        byte[] lenBytes = new byte[2];
+        if (str.Read(lenBytes) < 2)
+            throw PassStoreFileException.UnexpectedEndOfFile;
+        int len = BinaryPrimitives.ReadUInt16LittleEndian(lenBytes);
+        byte[] s = new byte[len];
+        if (str.Read(s) < len)
+            throw PassStoreFileException.UnexpectedEndOfFile;
+        return Encoding.UTF8.GetString(s);
+    }
+}
\ No newline at end of file
diff --git a/src/KeyKeeper/PasswordStore/IPassStore.cs b/src/KeyKeeper/PasswordStore/IPassStore.cs
new file mode 100644
index 0000000..68a1f6f
--- /dev/null
+++ b/src/KeyKeeper/PasswordStore/IPassStore.cs
@@ -0,0 +1,13 @@
+using KeyKeeper.PasswordStore.Crypto;
+
+namespace KeyKeeper.PasswordStore;
+
+public interface IPassStore
+{
+    bool Locked { get; }
+
+    IPassStoreDirectory GetRootDirectory();
+    int GetTotalEntryCount();
+    void Unlock(CompositeKey key);
+    void Lock();
+}
diff --git a/src/KeyKeeper/PasswordStore/IPassStoreDirectory.cs b/src/KeyKeeper/PasswordStore/IPassStoreDirectory.cs
new file mode 100644
index 0000000..b5c5acc
--- /dev/null
+++ b/src/KeyKeeper/PasswordStore/IPassStoreDirectory.cs
@@ -0,0 +1,7 @@
+using System.Collections.Generic;
+
+namespace KeyKeeper.PasswordStore;
+
+public interface IPassStoreDirectory : IEnumerable<PassStoreEntry>
+{
+}
diff --git a/src/KeyKeeper/PasswordStore/LoginField.cs b/src/KeyKeeper/PasswordStore/LoginField.cs
new file mode 100644
index 0000000..e4973d9
--- /dev/null
+++ b/src/KeyKeeper/PasswordStore/LoginField.cs
@@ -0,0 +1,16 @@
+using System;
+using static KeyKeeper.PasswordStore.FileFormatConstants;
+
+namespace KeyKeeper.PasswordStore;
+
+public struct LoginField
+{
+    public byte Type;
+    public Guid CustomFieldSubtype;
+    public required string Value;
+
+    public override string ToString()
+    {
+        return string.Format("LoginField(type={0} {1} value={2})", Type, Type == LOGIN_FIELD_CUSTOM_ID ? "customtype=" + CustomFieldSubtype : "", Value);
+    }
+}
\ No newline at end of file
diff --git a/src/KeyKeeper/PasswordStore/PassStoreEntry.cs b/src/KeyKeeper/PasswordStore/PassStoreEntry.cs
new file mode 100644
index 0000000..f9588bf
--- /dev/null
+++ b/src/KeyKeeper/PasswordStore/PassStoreEntry.cs
@@ -0,0 +1,78 @@
+using System;
+using System.IO;
+using KeyKeeper.PasswordStore.Crypto;
+using static KeyKeeper.PasswordStore.FileFormatConstants;
+
+namespace KeyKeeper.PasswordStore;
+
+public abstract class PassStoreEntry
+{
+    public Guid Id { get; set; }
+    public DateTime CreationDate { get; protected set; }
+    public DateTime ModificationDate { get; set; }
+    public Guid IconType { get; set; }
+    public string Name { get; set; }
+    public PassStoreEntryType Type { get; set; }
+
+    public void WriteToStream(Stream str)
+    {
+        MemoryStream tmp = new();
+        BinaryWriter wr = new(tmp);
+        wr.Write(Id.ToByteArray());
+        ulong timestamp = (ulong) new DateTimeOffset(CreationDate.ToUniversalTime()).ToUnixTimeSeconds();
+        FileFormatUtil.WriteVarUint16(tmp, timestamp);
+        timestamp = (ulong) new DateTimeOffset(ModificationDate.ToUniversalTime()).ToUnixTimeSeconds();
+        FileFormatUtil.WriteVarUint16(tmp, timestamp);
+        wr.Write(IconType.ToByteArray());
+        FileFormatUtil.WriteU16TaggedString(tmp, Name);
+        wr.Write(InnerSerialize());
+        byte[] serializedEntry = tmp.ToArray();
+        tmp.Dispose();
+
+        wr = new(str);
+        wr.Write7BitEncodedInt(serializedEntry.Length);
+        wr.Write(serializedEntry);
+    }
+
+    public static PassStoreEntry ReadFromStream(Stream str)
+    {
+        BinaryReader rd = new(str);
+        try
+        {
+            rd.Read7BitEncodedInt();
+
+            byte[] uuidBuffer = new byte[16];
+            if (rd.Read(uuidBuffer) < 16)
+                throw PassStoreFileException.UnexpectedEndOfFile;
+            Guid id = new Guid(uuidBuffer);
+
+            ulong timestamp = FileFormatUtil.ReadVarUint16(str);
+            DateTime createdAt = DateTimeOffset.FromUnixTimeSeconds((long)timestamp).UtcDateTime;
+            timestamp = FileFormatUtil.ReadVarUint16(str);
+            DateTime modifiedAt = DateTimeOffset.FromUnixTimeSeconds((long)timestamp).UtcDateTime;
+
+            if (rd.Read(uuidBuffer) < 16)
+                throw PassStoreFileException.UnexpectedEndOfFile;
+            Guid iconType = new Guid(uuidBuffer);
+
+            string name = FileFormatUtil.ReadU16TaggedString(str);
+
+            byte entryType = rd.ReadByte();
+            if (entryType == ENTRY_GROUP_ID)
+            {
+                return PassStoreEntryGroup.ReadFromStream(str, id, createdAt, modifiedAt, iconType, name);
+            } else if (entryType == ENTRY_PASS_ID)
+            {
+                return PassStoreEntryPassword.ReadFromStream(str, id, createdAt, modifiedAt, iconType, name);
+            } else
+            {
+                throw PassStoreFileException.InvalidPassStoreEntry;
+            }
+        } catch (EndOfStreamException)
+        {
+            throw PassStoreFileException.UnexpectedEndOfFile;
+        }
+    }
+
+    protected abstract byte[] InnerSerialize();
+}
diff --git a/src/KeyKeeper/PasswordStore/PassStoreEntryGroup.cs b/src/KeyKeeper/PasswordStore/PassStoreEntryGroup.cs
new file mode 100644
index 0000000..9624cec
--- /dev/null
+++ b/src/KeyKeeper/PasswordStore/PassStoreEntryGroup.cs
@@ -0,0 +1,97 @@
+using System;
+using System.Collections;
+using System.Collections.Generic;
+using System.IO;
+using static KeyKeeper.PasswordStore.FileFormatConstants;
+
+namespace KeyKeeper.PasswordStore;
+
+public class PassStoreEntryGroup : PassStoreEntry, IPassStoreDirectory
+{
+    public byte GroupType { get; set; }
+    public Guid? CustomGroupSubtype { get; set; }
+    public List<PassStoreEntry> ChildEntries { get; set; }
+
+    public PassStoreEntryGroup(Guid id, DateTime createdAt, DateTime modifiedAt,
+                               Guid iconType, string name, byte groupType,
+                               List<PassStoreEntry>? children = null,
+                               Guid? customGroupSubtype = null)
+    {
+        Id = id;
+        CreationDate = createdAt;
+        ModificationDate = modifiedAt;
+        IconType = iconType;
+        Name = name;
+        GroupType = groupType;
+        if (GroupType == GROUP_TYPE_CUSTOM && customGroupSubtype == null)
+            throw new ArgumentNullException("custom group type");
+        CustomGroupSubtype = customGroupSubtype;
+
+        ChildEntries = children ?? new();
+    }
+
+    public static PassStoreEntry ReadFromStream(Stream str, Guid id, DateTime createdAt, DateTime modifiedAt, Guid iconType, string name)
+    {
+        BinaryReader rd = new(str);
+        try
+        {
+            byte groupType = rd.ReadByte();
+            byte[] guidBuffer = new byte[16];
+            Guid? customGroupSubtype = null;
+            if (groupType == GROUP_TYPE_CUSTOM)
+            {
+                if (rd.Read(guidBuffer) < 16)
+                    throw PassStoreFileException.UnexpectedEndOfFile;
+                customGroupSubtype = new Guid(guidBuffer);
+            }
+
+            int entryCount = rd.Read7BitEncodedInt();
+            List<PassStoreEntry> children = new();
+            for (int i = 0; i < entryCount; i++)
+                children.Add(PassStoreEntry.ReadFromStream(str));
+            
+            return new PassStoreEntryGroup(
+                id, createdAt, modifiedAt,
+                iconType, name, groupType, children,
+                customGroupSubtype
+            );
+        } catch (EndOfStreamException)
+        {
+            throw PassStoreFileException.UnexpectedEndOfFile;
+        }
+    }
+
+    IEnumerator<PassStoreEntry> IEnumerable<PassStoreEntry>.GetEnumerator()
+    {
+        return ChildEntries.GetEnumerator();
+    }
+
+    IEnumerator IEnumerable.GetEnumerator()
+    {
+        return ChildEntries.GetEnumerator();
+    }
+
+    public override string ToString()
+    {
+        return string.Format(
+            "EntryGroup (id={0} name={1} chilren=[{2}])",
+            Id, Name, string.Join(", ", ChildEntries));
+    }
+
+    protected override byte[] InnerSerialize()
+    {
+        MemoryStream str = new();
+        str.WriteByte(ENTRY_GROUP_ID);
+
+        str.WriteByte(GroupType);
+        if (GroupType == GROUP_TYPE_CUSTOM)
+            str.Write(CustomGroupSubtype!.Value.ToByteArray());
+
+        BinaryWriter wr = new(str);
+        wr.Write7BitEncodedInt(ChildEntries.Count);
+        foreach (PassStoreEntry entry in ChildEntries)
+            entry.WriteToStream(str);
+
+        return str.ToArray();
+    }
+}
\ No newline at end of file
diff --git a/src/KeyKeeper/PasswordStore/PassStoreEntryPassword.cs b/src/KeyKeeper/PasswordStore/PassStoreEntryPassword.cs
new file mode 100644
index 0000000..09cece9
--- /dev/null
+++ b/src/KeyKeeper/PasswordStore/PassStoreEntryPassword.cs
@@ -0,0 +1,89 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using static KeyKeeper.PasswordStore.FileFormatConstants;
+
+namespace KeyKeeper.PasswordStore;
+
+public class PassStoreEntryPassword : PassStoreEntry
+{
+    public LoginField Username { get; set; }
+    public LoginField Password { get; set; }
+    public List<LoginField> ExtraFields { get; set; }
+
+    public PassStoreEntryPassword(Guid id, DateTime createdAt, DateTime modifiedAt, Guid iconType, string name, LoginField username, LoginField password, List<LoginField>? extras = null)
+    {
+        Id = id;
+        CreationDate = createdAt;
+        ModificationDate = modifiedAt;
+        IconType = iconType;
+        Name = name;
+        Username = username;
+        Password = password;
+        ExtraFields = extras ?? new();
+    }
+
+    public static PassStoreEntry ReadFromStream(Stream str, Guid id, DateTime createdAt, DateTime modifiedAt, Guid iconType, string name)
+    {
+        BinaryReader rd = new(str);
+        try
+        {
+            LoginField username = ReadField(str);
+            LoginField password = ReadField(str);
+            PassStoreEntryPassword entry = new(id, createdAt, modifiedAt, iconType, name, username, password);
+            int extraFieldCount = rd.Read7BitEncodedInt();
+            for (; extraFieldCount > 0; extraFieldCount--)
+                entry.ExtraFields.Add(ReadField(str));
+            return entry;
+        } catch (EndOfStreamException)
+        {
+            throw PassStoreFileException.UnexpectedEndOfFile;
+        }
+    }
+
+    public override string ToString()
+    {
+        return string.Format(
+            "EntryPassword(id={0} name={1} fields=[first={2} second={3} extra={4}])",
+            Id, Name, Username, Password, string.Join(", ", ExtraFields));
+    }
+
+    protected override byte[] InnerSerialize()
+    {
+        MemoryStream str = new();
+        str.WriteByte(ENTRY_PASS_ID);
+        WriteField(str, Username);
+        WriteField(str, Password);
+        BinaryWriter wr = new(str);
+        wr.Write7BitEncodedInt(ExtraFields.Count);
+        foreach (LoginField field in ExtraFields)
+            WriteField(str, field);
+        return str.ToArray();
+    }
+
+    private static void WriteField(Stream str, LoginField field)
+    {
+        str.WriteByte(field.Type);
+        if (field.Type == LOGIN_FIELD_CUSTOM_ID)
+            str.Write(field.CustomFieldSubtype.ToByteArray());
+        FileFormatUtil.WriteU16TaggedString(str, field.Value);
+    }
+
+    private static LoginField ReadField(Stream str)
+    {
+        int t = str.ReadByte();
+        if (t == -1)
+            throw PassStoreFileException.UnexpectedEndOfFile;
+        LoginField field = new() { Value = "" };
+        field.Type = (byte)t;
+        if (t == LOGIN_FIELD_CUSTOM_ID)
+        {
+            byte[] uuidBuffer = new byte[16];
+            if (str.Read(uuidBuffer) < 16)
+                throw PassStoreFileException.UnexpectedEndOfFile;
+            field.CustomFieldSubtype = new Guid(uuidBuffer);
+        }
+        field.Value = FileFormatUtil.ReadU16TaggedString(str);
+        return field;
+    }
+}
\ No newline at end of file
diff --git a/src/KeyKeeper/PasswordStore/PassStoreEntryType.cs b/src/KeyKeeper/PasswordStore/PassStoreEntryType.cs
new file mode 100644
index 0000000..8be01f8
--- /dev/null
+++ b/src/KeyKeeper/PasswordStore/PassStoreEntryType.cs
@@ -0,0 +1,7 @@
+namespace KeyKeeper.PasswordStore;
+
+public enum PassStoreEntryType
+{
+    Password,
+    Directory,
+}
diff --git a/src/KeyKeeper/PasswordStore/PassStoreFileAccessor.cs b/src/KeyKeeper/PasswordStore/PassStoreFileAccessor.cs
new file mode 100644
index 0000000..8169c34
--- /dev/null
+++ b/src/KeyKeeper/PasswordStore/PassStoreFileAccessor.cs
@@ -0,0 +1,395 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Security.Cryptography;
+using KeyKeeper.PasswordStore.Crypto;
+using KeyKeeper.PasswordStore.Crypto.KeyDerivation;
+using static KeyKeeper.PasswordStore.FileFormatConstants;
+
+namespace KeyKeeper.PasswordStore;
+
+/// <summary>
+/// Класс, содержащий реализацию доступа к хранилищу паролей
+/// </summary>
+public class PassStoreFileAccessor : IPassStore
+{
+    private const ushort FORMAT_VERSION_MAJOR = 0;
+    private const ushort FORMAT_VERSION_MINOR = 0;
+    private static readonly byte[] FORMAT_MAGIC = [0xf5, 0x3a, 0xa4, 0xb7, 0xeb, 0xd9, 0xc2, 0x12];
+
+    private string filename;
+    private byte[]? key;
+    private InnerEncryptionInfo? innerCrypto;
+    private PassStoreEntry? root;
+
+    public PassStoreFileAccessor(string filename, bool create, StoreCreationOptions? createOptions)
+    {
+        this.filename = filename;
+        this.key = null;
+        if (!create)
+        {
+            CheckStoreFile();
+        } else if (createOptions != null)
+        {
+            CreateNewAndUnlock(createOptions);
+        } else throw new ArgumentException("createOptions must not be null when creating a new store");
+    }
+
+    public bool Locked
+    {
+        get { return key == null; }
+    }
+
+    public IPassStoreDirectory GetRootDirectory()
+    {
+        if (Locked)
+            throw new InvalidOperationException();
+        return (IPassStoreDirectory)root!;
+    }
+
+    public int GetTotalEntryCount()
+    {
+        throw new NotImplementedException();
+    }
+
+    public void Unlock(CompositeKey key)
+    {
+        if (!Locked) return;
+
+        using FileStream file = new(filename, FileMode.Open, FileAccess.Read, FileShare.None);
+        FileHeader hdr = FileHeader.ReadFrom(file);
+
+        file.Seek((file.Position + 4096 - 1) / 4096 * 4096, SeekOrigin.Begin);
+
+        key.Salt = hdr.PreSalt;
+        this.key = hdr.KdfInfo.GetKdf().Derive(key, 32);
+        using OuterEncryptionReader cryptoReader = new(file, this.key, ((OuterAesHeader)hdr.OuterCryptoHeader).InitVector);
+        using BinaryReader rd = new(cryptoReader);
+
+        {
+            if (rd.ReadUInt32() != FILE_FIELD_BEGIN)
+                throw PassStoreFileException.InvalidBeginMarker;
+            Span<byte> marker = stackalloc byte[8];
+            if (rd.Read(marker) < 8)
+                throw PassStoreFileException.UnexpectedEndOfFile;
+            if (!marker.SequenceEqual(BEGIN_MARKER))
+                throw PassStoreFileException.InvalidBeginMarker;
+        }
+
+        while (true)
+        {
+            try
+            {
+                uint fileField = rd.ReadUInt32();
+                bool end = false;
+                switch (fileField)
+                {
+                    case FILE_FIELD_INNER_CRYPTO:
+                        ReadInnerCryptoInfo(cryptoReader);
+                        break;
+                    case FILE_FIELD_CONFIG:
+                        break;
+                    case FILE_FIELD_STORE:
+                        this.root = PassStoreEntry.ReadFromStream(cryptoReader);
+                        break;
+                    case FILE_FIELD_END:
+                        end = true;
+                        break;
+                }
+                if (end) break;
+            } catch (EndOfStreamException)
+            {
+                throw PassStoreFileException.UnexpectedEndOfFile;
+            }
+        }
+    }
+
+    public void Lock()
+    {
+        if (Locked) return;
+    }
+
+    /// <summary>
+    /// Проверяет внешнюю целостность файла хранилища, то есть:
+    /// 1. совпадает сигнатура (magic number)
+    /// 2. совпадает версия формата
+    /// 3. поля криптозаголовка корректны
+    /// </summary>
+    void CheckStoreFile()
+    {
+        using FileStream file = File.Open(filename, FileMode.Open, FileAccess.Read, FileShare.Read);
+        BinaryReader f = new(file);
+        byte[] magic = new byte[8];
+        if (f.Read(magic, 0, 8) < 8)
+        {
+            throw PassStoreFileException.UnexpectedEndOfFile;
+        }
+        if (!magic.SequenceEqual(FORMAT_MAGIC))
+        {
+            throw PassStoreFileException.IncorrectMagicNumber;
+        }
+
+        ushort version;
+        try
+        {
+            version = f.ReadUInt16();
+        }
+        catch (EndOfStreamException)
+        {
+            throw PassStoreFileException.UnexpectedEndOfFile;
+        }
+        if (version != FORMAT_VERSION_MAJOR)
+        {
+            throw PassStoreFileException.UnsupportedVersion;
+        }
+
+        try
+        {
+            version = f.ReadUInt16();
+        }
+        catch (EndOfStreamException)
+        {
+            throw PassStoreFileException.UnexpectedEndOfFile;
+        }
+        if (version != FORMAT_VERSION_MINOR)
+        {
+            throw PassStoreFileException.UnsupportedVersion;
+        }
+
+        OuterEncryptionUtil.CheckOuterEncryptionHeader(file);
+    }
+
+    private void CreateNewAndUnlock(StoreCreationOptions options)
+    {
+        using FileStream file = File.Open(filename, FileMode.Create, FileAccess.Write, FileShare.None);
+        FileHeader newHeader = FileHeader.Default();
+        newHeader.WriteTo(file);
+
+        options.Key.Salt = newHeader.PreSalt;
+
+        int randomPaddingLen = 4096 - (int)(file.Position % 4096);
+        if (randomPaddingLen > 0)
+        {
+            byte[] randomPadding = new byte[randomPaddingLen];
+            RandomNumberGenerator.Fill(randomPadding);
+            file.Write(randomPadding);
+        }
+
+        key = newHeader.KdfInfo.GetKdf().Derive(options.Key, 32);
+        // пока предполагаем что везде используется AES
+        OuterEncryptionWriter cryptoWriter = new(file, key, ((OuterAesHeader)newHeader.OuterCryptoHeader).InitVector);
+
+        BinaryWriter wr = new(cryptoWriter);
+
+        wr.Write(FILE_FIELD_BEGIN);
+        cryptoWriter.Write(BEGIN_MARKER);
+
+        byte[] innerKey = new byte[32];
+        RandomNumberGenerator.Fill(innerKey);
+        byte[] innerIv = new byte[16];
+        RandomNumberGenerator.Fill(innerIv);
+
+        wr.Write(FILE_FIELD_INNER_CRYPTO);
+        cryptoWriter.Write(innerKey);
+        cryptoWriter.Write(innerIv);
+
+        wr.Write(FILE_FIELD_CONFIG);
+
+        wr.Write(FILE_FIELD_STORE);
+        root = WriteInitialStoreTree(cryptoWriter);
+
+        wr.Write(FILE_FIELD_END);
+
+        cryptoWriter.Flush();
+        cryptoWriter.Dispose();
+    }
+
+    private PassStoreEntry WriteInitialStoreTree(OuterEncryptionWriter w)
+    {
+        PassStoreEntry root =
+            new PassStoreEntryGroup(
+                Guid.NewGuid(),
+                DateTime.UtcNow,
+                DateTime.UtcNow,
+                Guid.Empty,
+                "",
+                GROUP_TYPE_ROOT
+            );
+        root.WriteToStream(w);
+        return root;
+    }
+
+    private InnerEncryptionInfo ReadInnerCryptoInfo(Stream str)
+    {
+        byte[] key = new byte[32];
+        byte[] iv = new byte[16];
+        if (str.Read(key) < 32)
+            throw PassStoreFileException.UnexpectedEndOfFile;
+        if (str.Read(iv) < 16)
+            throw PassStoreFileException.UnexpectedEndOfFile;
+        return new(key, iv);
+    }
+
+    record FileHeader (
+        ushort FileVersionMajor,
+        ushort FileVersionMinor,
+        byte[] PreSalt,
+        OuterEncryptionHeader OuterCryptoHeader,
+        KdfHeader KdfInfo
+    )
+    {
+        public static FileHeader Default()
+        {
+            int saltLen = (MIN_MASTER_SALT_LEN + MAX_MASTER_SALT_LEN) / 2;
+            byte[] preSalt = new byte[saltLen];
+            RandomNumberGenerator.Fill(preSalt);
+
+            byte[] iv = new byte[16];
+            RandomNumberGenerator.Fill(iv);
+
+            byte[] aesKdfSeed = new byte[32];
+            RandomNumberGenerator.Fill(aesKdfSeed);
+
+            return new FileHeader
+            (
+                FORMAT_VERSION_MAJOR,
+                FORMAT_VERSION_MINOR,
+                preSalt,
+                new OuterAesHeader
+                (
+                    iv
+                ),
+                new AesKdfHeader
+                (
+                    200000,
+                    aesKdfSeed
+                )
+            );
+        }
+        public int WriteTo(Stream s)
+        {
+            int written = 0;
+
+            s.Write(FORMAT_MAGIC);
+            written += FORMAT_MAGIC.Length;
+
+            BinaryWriter wr = new(s);
+            wr.Write(FORMAT_VERSION_MAJOR);
+            wr.Write(FORMAT_VERSION_MINOR);
+            written += 4;
+
+            wr.Write((byte)PreSalt.Length);
+            s.Write(PreSalt);
+            written += 1 + PreSalt.Length;
+
+            if (OuterCryptoHeader is OuterAesHeader aes)
+            {
+                wr.Write(ENCRYPT_ALGO_AES);
+                s.Write(aes.InitVector);
+                written += 1 + aes.InitVector.Length;
+            }
+            if (KdfInfo is AesKdfHeader aesKdf)
+            {
+                long pos = s.Position;
+                wr.Write(KDF_TYPE_AESKDF);
+                wr.Write7BitEncodedInt(aesKdf.Rounds);
+                wr.Write(aesKdf.Seed);
+                written += (int)(s.Position - pos);
+            }
+            return written;
+        }
+
+        public static FileHeader ReadFrom(Stream s)
+        {
+            BinaryReader rd = new(s);
+            {
+                byte[] magic = new byte[8];
+                if (rd.Read(magic, 0, 8) < 8)
+                    throw PassStoreFileException.UnexpectedEndOfFile;
+                if (!magic.SequenceEqual(FORMAT_MAGIC))
+                    throw PassStoreFileException.IncorrectMagicNumber;
+            }
+            try
+            {
+                ushort major, minor;
+                major = rd.ReadUInt16();
+                minor = rd.ReadUInt16();
+                if (major != FORMAT_VERSION_MAJOR || minor != FORMAT_VERSION_MINOR)
+                    throw PassStoreFileException.UnsupportedVersion;
+
+                byte saltLen = rd.ReadByte();
+                if (saltLen < MIN_MASTER_SALT_LEN || saltLen > MAX_MASTER_SALT_LEN)
+                    throw PassStoreFileException.InvalidCryptoHeader;
+
+                byte[] salt = new byte[saltLen];
+                if (rd.Read(salt) < saltLen)
+                    throw PassStoreFileException.UnexpectedEndOfFile;
+
+                byte typeDiscrim = rd.ReadByte();
+                OuterEncryptionHeader outerEncrHdr;
+                if (typeDiscrim == ENCRYPT_ALGO_AES)
+                {
+                    byte[] iv = new byte[16];
+                    if (rd.Read(iv) < 16)
+                        throw PassStoreFileException.UnexpectedEndOfFile;
+                    outerEncrHdr = new OuterAesHeader(iv);
+                } else
+                {
+                    throw PassStoreFileException.InvalidCryptoHeader;
+                }
+
+                typeDiscrim = rd.ReadByte();
+                KdfHeader kdfHdr;
+                if (typeDiscrim == KDF_TYPE_AESKDF)
+                {
+                    int rounds = rd.Read7BitEncodedInt();
+                    byte[] seed = new byte[32];
+                    if (rd.Read(seed) < 32)
+                        throw PassStoreFileException.UnexpectedEndOfFile;
+                    kdfHdr = new AesKdfHeader(rounds, seed);
+                } else
+                {
+                    throw PassStoreFileException.InvalidCryptoHeader;
+                }
+
+                return new FileHeader(
+                    major, minor, salt,
+                    outerEncrHdr, kdfHdr
+                );
+            }
+            catch (EndOfStreamException)
+            {
+                throw PassStoreFileException.UnexpectedEndOfFile;
+            }
+        }
+    };
+
+    record OuterEncryptionHeader {}
+
+    record OuterAesHeader(
+        byte[] InitVector
+    ) : OuterEncryptionHeader;
+
+    abstract record KdfHeader
+    {
+        public abstract MasterKeyDerivationFunction GetKdf();
+    }
+
+    record AesKdfHeader(
+        int Rounds,
+        byte[] Seed
+    ) : KdfHeader
+    {
+        public override MasterKeyDerivationFunction GetKdf()
+        {
+            return new AesKdf(Rounds, Seed);
+        }
+    }
+
+    record struct InnerEncryptionInfo(
+        byte[] Key,
+        byte[] Iv
+    )
+    {}
+}
diff --git a/src/KeyKeeper/PasswordStore/PassStoreFileException.cs b/src/KeyKeeper/PasswordStore/PassStoreFileException.cs
new file mode 100644
index 0000000..35d5a03
--- /dev/null
+++ b/src/KeyKeeper/PasswordStore/PassStoreFileException.cs
@@ -0,0 +1,18 @@
+using System;
+
+namespace KeyKeeper.PasswordStore;
+
+public class PassStoreFileException : Exception
+{
+    public static readonly PassStoreFileException UnexpectedEndOfFile = new("unexpected EOF");
+    public static readonly PassStoreFileException IncorrectMagicNumber = new("incorrect signature (magic number)");
+    public static readonly PassStoreFileException UnsupportedVersion = new("unsupported format version");
+    public static readonly PassStoreFileException InvalidCryptoHeader = new("invalid encryption header");
+    public static readonly PassStoreFileException ContentHMACMismatch = new("content HMAC mismatch");
+    public static readonly PassStoreFileException InvalidPassStoreEntry = new("invalid store entry");
+    public static readonly PassStoreFileException InvalidBeginMarker = new("invalid marker of the beginning of data");
+
+    public PassStoreFileException(string description): base(description)
+    {
+    }
+}
diff --git a/src/KeyKeeper/PasswordStore/StoreCreationOptions.cs b/src/KeyKeeper/PasswordStore/StoreCreationOptions.cs
new file mode 100644
index 0000000..e35eadf
--- /dev/null
+++ b/src/KeyKeeper/PasswordStore/StoreCreationOptions.cs
@@ -0,0 +1,9 @@
+using KeyKeeper.PasswordStore.Crypto;
+
+namespace KeyKeeper.PasswordStore;
+
+public record StoreCreationOptions
+{
+    public int LockTimeoutSeconds { get; init; }
+    public CompositeKey Key { get; init; }
+}
\ No newline at end of file
diff --git a/src/KeyKeeper/RepositoryWindow.axaml.cs b/src/KeyKeeper/RepositoryWindow.axaml.cs
index 56f7f87..5bb3fc9 100644
--- a/src/KeyKeeper/RepositoryWindow.axaml.cs
+++ b/src/KeyKeeper/RepositoryWindow.axaml.cs
@@ -1,13 +1,25 @@
+using System;
 using Avalonia;
 using Avalonia.Controls;
 using Avalonia.Markup.Xaml;
+using KeyKeeper.PasswordStore;
+using KeyKeeper.PasswordStore.Crypto;
 
 namespace KeyKeeper;
 
 public partial class RepositoryWindow: Window
 {
+    public IPassStore? PassStore { private get; init; }
+
     public RepositoryWindow()
     {
         InitializeComponent();
     }
+
+    protected override void OnOpened(EventArgs e)
+    {
+        base.OnOpened(e);
+        if (PassStore!.Locked)
+            PassStore.Unlock(new CompositeKey("blablabla", null));
+    }
 }
\ No newline at end of file
diff --git a/src/KeyKeeper/Views/MainWindow.axaml.cs b/src/KeyKeeper/Views/MainWindow.axaml.cs
index ec9a8a1..b55c457 100644
--- a/src/KeyKeeper/Views/MainWindow.axaml.cs
+++ b/src/KeyKeeper/Views/MainWindow.axaml.cs
@@ -3,6 +3,7 @@ using Avalonia.Controls;
 using Avalonia.Input;
 using Avalonia.Interactivity;
 using Avalonia.Platform.Storage;
+using KeyKeeper.PasswordStore;
 using KeyKeeper.ViewModels;
 using System;
 using System.Collections.Generic;
@@ -39,7 +40,11 @@ namespace KeyKeeper.Views
                 if (file.TryGetLocalPath() is string path)
                 {
                     (DataContext as MainWindowViewModel)!.CreateVault(path);
-                    OpenRepositoryWindow();
+                    OpenRepositoryWindow(new PassStoreFileAccessor(path, true, new StoreCreationOptions()
+                    {
+                        Key = new PasswordStore.Crypto.CompositeKey("blablabla", null),
+                        LockTimeoutSeconds = 800,
+                    }));
                 }
             }
         }
@@ -70,16 +75,17 @@ namespace KeyKeeper.Views
                 if (file.TryGetLocalPath() is string path)
                 {
                     (DataContext as MainWindowViewModel)!.OpenVault(path);
-                    OpenRepositoryWindow();
+                    OpenRepositoryWindow(new PassStoreFileAccessor(path, false, null));
                 }
             }
         }
 
-        private void OpenRepositoryWindow()
+        private void OpenRepositoryWindow(IPassStore store)
         {
             var repositoryWindow = new RepositoryWindow()
             {
                 DataContext = this.DataContext,
+                PassStore = store,
                 WindowStartupLocation = WindowStartupLocation.CenterScreen
             };
             repositoryWindow.Closed += (s, e) => this.Show();