SabreTools/NDecrypt
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Reduce complexity of partition keys

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This commit is contained in:
Matt Nadareski
2026-03-22 00:25:19 -04:00
parent a518f1fd94
commit 5f000cac8b
2 changed files with 63 additions and 77 deletions
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88
NDecrypt.Core/PartitionKeys.cs
View File

@@ -9,61 +9,31 @@ namespace NDecrypt.Core
/// </summary>
public class PartitionKeys
{
public byte[] KeyX { get; private set; }
public byte[] KeyX2C { get; }
public byte[] KeyY { get; }
public byte[] NormalKey { get; private set; }
public byte[] NormalKey2C { get; }
/// <summary>
/// Decryption args to use while processing
/// </summary>
private readonly ThreeDSDecryptArgs _decryptArgs;
/// <summary>
/// Indicates if development images are expected
/// </summary>
private readonly bool _development;
private readonly byte[] KeyY;
/// <summary>
/// Create a new set of keys for a given partition
/// </summary>
/// <param name="args">Decryption args representing available keys</param>
/// <param name="signature">RSA-2048 signature from the partition</param>
/// <param name="masks">BitMasks from the partition or backup header</param>
/// <param name="method">CryptoMethod from the partition or backup header</param>
/// <param name="development">Determine if development keys are used</param>
public PartitionKeys(ThreeDSDecryptArgs args, byte[]? signature, BitMasks masks, CryptoMethod method, bool development)
/// <param name="hardwareConstant">AES hardware constant to use</param>
/// <param name="keyX">KeyX value to assign based on crypto method and development status</param>
/// <param name="KeyX2C">KeyX value to assign based on development status</param>
public PartitionKeys(byte[]? signature, BitMasks masks, byte[] hardwareConstant, byte[] keyX, byte[] keyX0x2C)
{
// Validate inputs
if (signature is not null && signature.Length < 16)
throw new ArgumentOutOfRangeException(nameof(signature), $"{nameof(signature)} must be at least 16 bytes");
// Set fields for future use
_decryptArgs = args;
_development = development;
// Set the standard KeyX values
KeyX = new byte[16];
KeyX2C = development ? _decryptArgs.DevKeyX0x2C : _decryptArgs.KeyX0x2C;
// Backup headers can't have a KeyY value set
KeyY = new byte[16];
if (signature is not null)
Array.Copy(signature, KeyY, 16);
// Set the standard normal key values
NormalKey = new byte[16];
NormalKey2C = KeyX2C.RotateLeft(2);
NormalKey2C = NormalKey2C.Xor(KeyY);
NormalKey2C = NormalKey2C.Add(add: _decryptArgs.AESHardwareConstant);
NormalKey2C = NormalKey2C.RotateLeft(87);
// Special case for zero-key
#if NET20 || NET35
if ((masks & BitMasks.FixedCryptoKey) > 0)
@@ -77,46 +47,22 @@ namespace NDecrypt.Core
return;
}
// Set KeyX values based on crypto method
switch (method)
{
case CryptoMethod.Original:
Console.WriteLine("Encryption Method: Key 0x2C");
KeyX = development ? _decryptArgs.DevKeyX0x2C : _decryptArgs.KeyX0x2C;
break;
case CryptoMethod.Seven:
Console.WriteLine("Encryption Method: Key 0x25");
KeyX = development ? _decryptArgs.DevKeyX0x25 : _decryptArgs.KeyX0x25;
break;
case CryptoMethod.NineThree:
Console.WriteLine("Encryption Method: Key 0x18");
KeyX = development ? _decryptArgs.DevKeyX0x18 : _decryptArgs.KeyX0x18;
break;
case CryptoMethod.NineSix:
Console.WriteLine("Encryption Method: Key 0x1B");
KeyX = development ? _decryptArgs.DevKeyX0x1B : _decryptArgs.KeyX0x1B;
break;
// This should never happen
default:
Console.WriteLine("Encryption Method: UNSUPPORTED");
break;
}
// Set the normal key based on the new KeyX value
NormalKey = KeyX.RotateLeft(2);
// Set the standard normal key values
NormalKey = keyX.RotateLeft(2);
NormalKey = NormalKey.Xor(KeyY);
NormalKey = NormalKey.Add(_decryptArgs.AESHardwareConstant);
NormalKey = NormalKey.Add(hardwareConstant);
NormalKey = NormalKey.RotateLeft(87);
NormalKey2C = keyX0x2C.RotateLeft(2);
NormalKey2C = NormalKey2C.Xor(KeyY);
NormalKey2C = NormalKey2C.Add(hardwareConstant);
NormalKey2C = NormalKey2C.RotateLeft(87);
}
/// <summary>
/// Set RomFS values based on the bit masks
/// </summary>
public void SetRomFSValues(BitMasks masks)
public void SetRomFSValues(BitMasks masks, byte[] hardwareConstant, byte[] keyX0x2C)
{
// NormalKey has a constant value for zero-key
#if NET20 || NET35
@@ -130,11 +76,9 @@ namespace NDecrypt.Core
}
// Encrypting RomFS for partitions 1 and up always use Key0x2C
KeyX = _development ? _decryptArgs.DevKeyX0x2C : _decryptArgs.KeyX0x2C;
NormalKey = KeyX.RotateLeft(2);
NormalKey = keyX0x2C.RotateLeft(2);
NormalKey = NormalKey.Xor(KeyY);
NormalKey = NormalKey.Add(_decryptArgs.AESHardwareConstant);
NormalKey = NormalKey.Add(hardwareConstant);
NormalKey = NormalKey.RotateLeft(87);
}
}

52
NDecrypt.Core/ThreeDSTool.cs
View File

@@ -32,6 +32,40 @@ namespace NDecrypt.Core
_decryptArgs = decryptArgs;
}
#region Common
/// <summary>
/// Get KeyX value for a crypto method and development status combination
/// </summary>
private byte[] GetKeyXForCryptoMethod(CryptoMethod method)
{
switch (method)
{
case CryptoMethod.Original:
Console.WriteLine("Encryption Method: Key 0x2C");
return _development ? _decryptArgs.DevKeyX0x2C : _decryptArgs.KeyX0x2C;
case CryptoMethod.Seven:
Console.WriteLine("Encryption Method: Key 0x25");
return _development ? _decryptArgs.DevKeyX0x25 : _decryptArgs.KeyX0x25;
case CryptoMethod.NineThree:
Console.WriteLine("Encryption Method: Key 0x18");
return _development ? _decryptArgs.DevKeyX0x18 : _decryptArgs.KeyX0x18;
case CryptoMethod.NineSix:
Console.WriteLine("Encryption Method: Key 0x1B");
return _development ? _decryptArgs.DevKeyX0x1B : _decryptArgs.KeyX0x1B;
// This should never happen
default:
Console.WriteLine("Encryption Method: UNSUPPORTED");
return [];
}
}
#endregion
#region Decrypt
/// <inheritdoc/>
@@ -165,12 +199,15 @@ namespace NDecrypt.Core
return;
// Get partition-specific values
byte[]? rsaSignature = partition.RSA2048Signature;
byte[]? signature = partition.RSA2048Signature;
BitMasks masks = cart.GetBitMasks(index);
CryptoMethod method = cart.GetCryptoMethod(index);
// Get the partition keys
_keysMap[index] = new PartitionKeys(_decryptArgs, rsaSignature, masks, method, _development);
byte[] hardwareConstant = _decryptArgs.AESHardwareConstant;
byte[] keyX = GetKeyXForCryptoMethod(method);
byte[] keyX0x2C = _development ? _decryptArgs.DevKeyX0x2C : _decryptArgs.KeyX0x2C;
_keysMap[index] = new PartitionKeys(signature, masks, hardwareConstant, keyX, keyX0x2C);
}
/// <summary>
@@ -583,12 +620,15 @@ namespace NDecrypt.Core
return;
// Get partition-specific values
byte[]? rsaSignature = partition.RSA2048Signature;
byte[]? signature = partition.RSA2048Signature;
BitMasks masks = backupHeader.Flags.BitMasks;
CryptoMethod method = backupHeader.Flags.CryptoMethod;
// Get the partition keys
_keysMap[index] = new PartitionKeys(_decryptArgs, rsaSignature, masks, method, _development);
byte[] hardwareConstant = _decryptArgs.AESHardwareConstant;
byte[] keyX = GetKeyXForCryptoMethod(method);
byte[] keyX0x2C = _development ? _decryptArgs.DevKeyX0x2C : _decryptArgs.KeyX0x2C;
_keysMap[index] = new PartitionKeys(signature, masks, hardwareConstant, keyX, keyX0x2C);
}
/// <summary>
@@ -820,7 +860,9 @@ namespace NDecrypt.Core
if (index > 0)
{
var backupHeader = cart.BackupHeader;
_keysMap[index].SetRomFSValues(backupHeader!.Flags!.BitMasks);
_keysMap[index].SetRomFSValues(backupHeader.Flags.BitMasks,
hardwareConstant: _decryptArgs.AESHardwareConstant,
keyX0x2C: _development ? _decryptArgs.DevKeyX0x2C : _decryptArgs.KeyX0x2C);
}
// Create the RomFS AES cipher for this partition