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Switched name encoding to more reliable Secomba Base4K implementation
1 parent 29c32d8 commit 15bbecf

4 files changed

Lines changed: 296 additions & 5 deletions

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‎src/Core/SecureFolderFS.Core.Cryptography/Cipher/SecombaBase4K.cs‎

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// Some parts of the following code were used from Secomba/Base4K on the MIT License basis.
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// See the associated license file for more information.
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using System;
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using System.Buffers;
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using System.Collections.Generic;
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using System.IO;
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using System.Runtime.CompilerServices;
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using System.Text;
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namespace SecureFolderFS.Core.Cryptography.Cipher
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{
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public enum Base4KVersion
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{
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V1,
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V2
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}
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public static class SecombaBase4K
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{
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// Base addresses for mapping regions
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private const int BASE_FLAG_START = 0x04000;
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private const int BASE1_START = 0x06000;
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private const int BASE1_START_LEGACY = 0x05000;
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// Sizes of each mapping region
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private const int BASE_FLAG_SIZE = 0x100;
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private const int BASE1_SIZE = 0x01000;
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private static readonly UTF8Encoding Utf8Encoding = new UTF8Encoding(true, true);
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/// <summary>
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/// Encodes the specified raw bytes as a Base4K string, mapping each group of bits
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/// to Unicode characters in a specific range, suitable for use as file names.
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/// </summary>
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/// <param name="raw">The raw bytes to encode.</param>
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/// <param name="version">The version of Base4K encoding to use. Defaults to <see cref="Base4KVersion.V2"/>.</param>
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/// <returns>A Base4K-encoded string representation of the input bytes.</returns>
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/// <exception cref="ArgumentException">Thrown when <paramref name="raw"/> is empty or too short to encode.</exception>
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[SkipLocalsInit]
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public static string Encode(ReadOnlySpan<byte> raw, Base4KVersion version = Base4KVersion.V2)
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{
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if (raw.Length <= 1)
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throw new ArgumentException("Input must be at least 2 bytes long.", nameof(raw));
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var maxByteCount = (raw.Length + 1) * 3;
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var rentedBuffer = ArrayPool<byte>.Shared.Rent(maxByteCount);
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try
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{
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var buffer = rentedBuffer.AsSpan();
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var bufferPos = 0;
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Span<byte> utf8Buffer = stackalloc byte[4];
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int offset;
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for (var i = 0; i < raw.Length * 2 - 2; i += 3)
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{
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offset = i % 2 == 0
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? ((raw[i / 2] << 4) | ((raw[i / 2 + 1] >> 4) & 0x0f)) & 0x0fff
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: ((raw[i / 2] << 8) | (raw[i / 2 + 1] & 0xff)) & 0x0fff;
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offset += version == Base4KVersion.V1 ? BASE1_START_LEGACY : BASE1_START;
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var written = ToUtf8(offset, utf8Buffer);
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utf8Buffer.Slice(0, written).CopyTo(buffer.Slice(bufferPos));
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bufferPos += written;
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}
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if ((raw.Length * 2) % 3 == 2)
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{
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offset = (raw[^1] & 0xff) + BASE_FLAG_START;
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var written = ToUtf8(offset, utf8Buffer);
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utf8Buffer.Slice(0, written).CopyTo(buffer.Slice(bufferPos));
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bufferPos += written;
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}
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else if ((raw.Length * 2) % 3 == 1)
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{
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offset = (raw[^1] & 0x0f) + BASE_FLAG_START;
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var written = ToUtf8(offset, utf8Buffer);
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utf8Buffer.Slice(0, written).CopyTo(buffer.Slice(bufferPos));
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bufferPos += written;
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}
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return Utf8Encoding.GetString(buffer.Slice(0, bufferPos));
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}
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finally
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{
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ArrayPool<byte>.Shared.Return(rentedBuffer);
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}
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}
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/// <summary>
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/// Decodes a Base4K-encoded string back to the original raw bytes.
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/// Attempts decoding with both V2 and V1 (legacy) base addresses automatically.
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/// </summary>
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/// <param name="encoded">The Base4K-encoded string to decode.</param>
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/// <returns>The decoded bytes, or <see langword="null"/> if decoding failed due to invalid or malformed input.</returns>
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public static byte[]? Decode(ReadOnlySpan<char> encoded)
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{
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return DecodeInternal(encoded, BASE1_START) ?? DecodeInternal(encoded, BASE1_START_LEGACY);
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}
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private static byte[]? DecodeInternal(ReadOnlySpan<char> encoded, int base1Start)
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{
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var byteCount = Utf8Encoding.GetByteCount(encoded);
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var encBytes = new byte[byteCount];
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var written = Utf8Encoding.GetBytes(encoded, encBytes);
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using var memoryStream = new MemoryStream();
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var rentedCollector = ArrayPool<int>.Shared.Rent(written / 3 + 1);
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var collectorCount = 0;
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try
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{
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for (var i = 0; i < written;)
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{
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int nrOfBytes;
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if ((encBytes[i] & 0x80) == 0)
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{
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// 1 byte
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nrOfBytes = 1;
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}
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else if ((encBytes[i] & 0x40) == 0)
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{
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// Continuation byte — invalid as a leading byte
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return null;
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}
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else if ((encBytes[i] & 0x20) == 0)
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{
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// 2 bytes
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nrOfBytes = 2;
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}
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else if ((encBytes[i] & 0x10) == 0)
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{
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// 3 bytes
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nrOfBytes = 3;
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}
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else if ((encBytes[i] & 0x08) == 0)
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{
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// 4 bytes
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nrOfBytes = 4;
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}
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else
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{
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// Invalid leading byte
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return null;
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}
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var code = ToCode(encBytes, i, nrOfBytes);
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i += nrOfBytes;
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if (!(code >= base1Start && code < base1Start + BASE1_SIZE))
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{
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if (i < written || !(code >= BASE_FLAG_START && code < BASE_FLAG_START + BASE_FLAG_SIZE))
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return null;
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}
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rentedCollector[collectorCount++] = code;
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}
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for (var i = 0; i < collectorCount; i++)
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{
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if (rentedCollector[i] >= base1Start)
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rentedCollector[i] -= base1Start;
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else
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{
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rentedCollector[i] -= BASE_FLAG_START;
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if (i % 2 == 0)
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memoryStream.WriteByte((byte)rentedCollector[i]);
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else
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memoryStream.WriteByte((byte)(((rentedCollector[i - 1] << 4) | ((rentedCollector[i] & 0x0f)) & 0xff)));
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break;
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}
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if (i % 2 == 0)
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memoryStream.WriteByte((byte)(rentedCollector[i] >> 4));
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else
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{
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memoryStream.WriteByte((byte)(((rentedCollector[i - 1] << 4) | ((rentedCollector[i] & 0x0f00) >> 8)) & 0xff));
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memoryStream.WriteByte((byte)(rentedCollector[i] & 0xff));
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}
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}
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}
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finally
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{
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ArrayPool<int>.Shared.Return(rentedCollector);
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}
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return memoryStream.ToArray();
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}
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private static int ToUtf8(int code, Span<byte> destination)
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{
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switch (code)
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{
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case > 0xffff:
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{
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destination[0] = (byte)(0xf0 | ((code >> 18) & 0x07));
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destination[1] = (byte)(0x80 | ((code >> 12) & 0x3f));
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destination[2] = (byte)(0x80 | ((code >> 6) & 0x3f));
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destination[3] = (byte)(0x80 | (code & 0x3f));
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return 4;
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}
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case > 0x7ff:
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{
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destination[0] = (byte)(0xe0 | ((code >> 12) & 0x0f));
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destination[1] = (byte)(0x80 | ((code >> 6) & 0x3f));
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destination[2] = (byte)(0x80 | (code & 0x3f));
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return 3;
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}
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case > 0x7f:
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{
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destination[0] = (byte)(0xc0 | ((code >> 6) & 0x1f));
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destination[1] = (byte)(0x80 | (code & 0x3f));
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return 2;
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}
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default:
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{
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destination[0] = (byte)(code & 0x7f);
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return 1;
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}
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}
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}
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private static int ToCode(ReadOnlySpan<byte> utf8Char, int offset, int length)
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{
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var result = 0;
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switch (length)
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{
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case 1:
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{
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result |= utf8Char[offset];
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break;
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}
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case 2:
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{
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result |= (utf8Char[offset + 0] & 0x1f) << 6;
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result |= (utf8Char[offset + 1] & 0x3f);
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break;
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}
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case 3:
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{
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result |= (utf8Char[offset + 0] & 0x0f) << 12;
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result |= (utf8Char[offset + 1] & 0x3f) << 6;
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result |= (utf8Char[offset + 2] & 0x3f);
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break;
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}
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case 4:
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{
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result |= (utf8Char[offset + 0] & 0x07) << 18;
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result |= (utf8Char[offset + 1] & 0x3f) << 12;
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result |= (utf8Char[offset + 2] & 0x3f) << 6;
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result |= (utf8Char[offset + 3] & 0x3f);
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break;
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}
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}
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return result;
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}
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}
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}

‎src/Core/SecureFolderFS.Core.Cryptography/NameCrypt/BaseNameCrypt.cs‎

Lines changed: 4 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -2,7 +2,7 @@
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using System.Buffers.Text;
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using System.Runtime.CompilerServices;
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using System.Text;
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using Lex4K;
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using SecureFolderFS.Core.Cryptography.Cipher;
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namespace SecureFolderFS.Core.Cryptography.NameCrypt
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{
@@ -35,7 +35,7 @@ public virtual string EncryptName(ReadOnlySpan<char> plaintextName, ReadOnlySpan
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return fileNameEncodingId switch
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{
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Constants.CipherId.ENCODING_BASE64URL => Base64Url.EncodeToString(ciphertextNameBuffer),
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Constants.CipherId.ENCODING_BASE4K => Base4K.EncodeChainToString(ciphertextNameBuffer),
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Constants.CipherId.ENCODING_BASE4K => SecombaBase4K.Encode(ciphertextNameBuffer),
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_ => throw new ArgumentOutOfRangeException(nameof(fileNameEncodingId))
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};
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}
@@ -46,7 +46,7 @@ public virtual string EncryptName(ReadOnlySpan<char> plaintextName, ReadOnlySpan
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{
4747
try
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{
49-
if (!ciphertextName.IsNormalized(NORMALIZATION))
49+
if (fileNameEncodingId == Constants.CipherId.ENCODING_BASE4K && !ciphertextName.IsNormalized(NORMALIZATION))
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{
5151
var normalizedLength = ciphertextName.GetNormalizedLength(NORMALIZATION);
5252
var destination = normalizedLength < 256 ? stackalloc char[normalizedLength] : new char[normalizedLength];
@@ -73,7 +73,7 @@ public virtual string EncryptName(ReadOnlySpan<char> plaintextName, ReadOnlySpan
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var decoded = fileNameEncodingId switch
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{
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Constants.CipherId.ENCODING_BASE64URL => Base64Url.DecodeFromChars(name),
76-
Constants.CipherId.ENCODING_BASE4K => Base4K.DecodeChainToNewBuffer(name),
76+
Constants.CipherId.ENCODING_BASE4K => SecombaBase4K.Decode(name),
7777
_ => throw new ArgumentOutOfRangeException(nameof(fileNameEncodingId))
7878
};
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‎src/Core/SecureFolderFS.Core.FileSystem/Helpers/Paths/Abstract/AbstractPathHelpers.cs‎

Lines changed: 0 additions & 1 deletion
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@@ -1,6 +1,5 @@
11
using System;
22
using System.IO;
3-
using System.Text;
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using SecureFolderFS.Core.Cryptography;
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namespace SecureFolderFS.Core.FileSystem.Helpers.Paths.Abstract

‎src/Platforms/SecureFolderFS.UI/Assets/Licenses/SecombaBase4K LICENSE‎

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Secomba Base4K
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https://github.com/secomba/base4k/blob/master/LICENSE
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MIT
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https://github.com/secomba/base4k
5+
6+
The MIT License (MIT)
7+
8+
Copyright (c) 2014 Secomba GmbH
9+
10+
Permission is hereby granted, free of charge, to any person obtaining a copy
11+
of this software and associated documentation files (the "Software"), to deal
12+
in the Software without restriction, including without limitation the rights
13+
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
14+
copies of the Software, and to permit persons to whom the Software is
15+
furnished to do so, subject to the following conditions:
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17+
The above copyright notice and this permission notice shall be included in all
18+
copies or substantial portions of the Software.
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20+
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
22+
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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SOFTWARE.

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