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VolumeWiiCrypted: Decryption optimization #1969

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merged 2 commits into from Feb 8, 2015
Merged

VolumeWiiCrypted: Decryption optimization #1969

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521ccd7
VolumeWiiCrypted: Decryption optimization
JosJuice Jan 26, 2015
28b441e
VolumeWiiCrypted: Replace some hardcoded values with constants
JosJuice Feb 8, 2015
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39 changes: 22 additions & 17 deletions Source/Core/DiscIO/VolumeWiiCrypted.cpp
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Expand Up @@ -33,7 +33,7 @@ CVolumeWiiCrypted::CVolumeWiiCrypted(IBlobReader* _pReader, u64 _VolumeOffset,
m_LastDecryptedBlockOffset(-1)
{
aes_setkey_dec(m_AES_ctx.get(), _pVolumeKey, 128);
m_pBuffer = new u8[0x8000];
m_pBuffer = new u8[s_block_total_size];
}

bool CVolumeWiiCrypted::ChangePartition(u64 offset)
Expand All @@ -47,7 +47,6 @@ bool CVolumeWiiCrypted::ChangePartition(u64 offset)
return true;
}


CVolumeWiiCrypted::~CVolumeWiiCrypted()
{
delete[] m_pBuffer;
Expand All @@ -66,36 +65,42 @@ bool CVolumeWiiCrypted::Read(u64 _ReadOffset, u64 _Length, u8* _pBuffer, bool de

while (_Length > 0)
{
static unsigned char IV[16];

// math block offset
u64 Block = _ReadOffset / 0x7C00;
u64 Offset = _ReadOffset % 0x7C00;

// read current block
if (!m_pReader->Read(m_VolumeOffset + m_dataOffset + Block * 0x8000, 0x8000, m_pBuffer))
return(false);
// Calculate block offset
u64 Block = _ReadOffset / s_block_data_size;
u64 Offset = _ReadOffset % s_block_data_size;

if (m_LastDecryptedBlockOffset != Block)
{
memcpy(IV, m_pBuffer + 0x3d0, 16);
aes_crypt_cbc(m_AES_ctx.get(), AES_DECRYPT, 0x7C00, IV, m_pBuffer + 0x400, m_LastDecryptedBlock);
// Read the current block
if (!m_pReader->Read(m_VolumeOffset + m_dataOffset + Block * s_block_total_size, s_block_total_size, m_pBuffer))
return false;

// Decrypt the block's data.
// 0x3D0 - 0x3DF in m_pBuffer will be overwritten,
// but that won't affect anything, because we won't
// use the content of m_pBuffer anymore after this
aes_crypt_cbc(m_AES_ctx.get(), AES_DECRYPT, s_block_data_size, m_pBuffer + 0x3D0,
m_pBuffer + s_block_header_size, m_LastDecryptedBlock);
m_LastDecryptedBlockOffset = Block;

// The only thing we currently use from the 0x000 - 0x3FF part
// of the block is the IV (at 0x3D0), but it also contains SHA-1
// hashes that IOS uses to check that discs aren't tampered with.
// http://wiibrew.org/wiki/Wii_Disc#Encrypted
}

// copy the encrypted data
u64 MaxSizeToCopy = 0x7C00 - Offset;
// Copy the decrypted data
u64 MaxSizeToCopy = s_block_data_size - Offset;
u64 CopySize = (_Length > MaxSizeToCopy) ? MaxSizeToCopy : _Length;
memcpy(_pBuffer, &m_LastDecryptedBlock[Offset], (size_t)CopySize);

// increase buffers
// Update offsets
_Length -= CopySize;
_pBuffer += CopySize;
_ReadOffset += CopySize;
}

return(true);
return true;
}

bool CVolumeWiiCrypted::GetTitleID(u8* _pBuffer) const
Expand Down
6 changes: 5 additions & 1 deletion Source/Core/DiscIO/VolumeWiiCrypted.h
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Expand Up @@ -44,6 +44,10 @@ class CVolumeWiiCrypted : public IVolume
bool ChangePartition(u64 offset) override;

private:
static const unsigned int s_block_header_size = 0x0400;
static const unsigned int s_block_data_size = 0x7C00;
static const unsigned int s_block_total_size = s_block_header_size + s_block_data_size;

std::unique_ptr<IBlobReader> m_pReader;
std::unique_ptr<aes_context> m_AES_ctx;

Expand All @@ -53,7 +57,7 @@ class CVolumeWiiCrypted : public IVolume
u64 m_dataOffset;

mutable u64 m_LastDecryptedBlockOffset;
mutable unsigned char m_LastDecryptedBlock[0x8000];
mutable unsigned char m_LastDecryptedBlock[s_block_data_size];
};

} // namespace