public static void DecryptNCA(Stream input, long offset)
{
var keyset = new Keyset();
using (var bw = new BinaryWriterX(input, true))
using (var br = new BinaryReaderX(input, true))
{
br.BaseStream.Position = offset;
//Decrypt NCA Header
var enc_header = br.ReadBytes(0x400);
var magic = enc_header.GetElements(0x200, 4).Aggregate("", (o, b) => o + (char)b);
var headerPart = new byte[0x400];
var headerPart2 = new byte[0x800];
if (magic != "NCA2" && magic != "NCA3")
{
headerPart = Decryption.XTS128(enc_header, keyset.ncaHeaderKey, 0x200, true);
magic = headerPart.GetElements(0x200, 4).Aggregate("", (o, b) => o + (char)b);
bw.BaseStream.Position = offset;
bw.Write(headerPart);
if (magic == "NCA3")
{
headerPart2 = Decryption.XTS128(br.ReadBytes(0x800), keyset.ncaHeaderKey, 0x200, true, 2);
bw.BaseStream.Position = offset + 0x400;
bw.Write(headerPart2);
}
else if (magic == "NCA2")
{
for (int i = 0; i < 4; i++)
{
var buffer = Decryption.XTS128(br.ReadBytes(0x200), keyset.ncaHeaderKey, 0x200, true);
Array.Copy(buffer, 0, headerPart2, i * 0x200, 0x200);
bw.BaseStream.Position -= 0x200;
bw.Write(buffer);
}
}
else
{
throw new InvalidDataException("Invalid NCA Header! Are the keys correct?");
}
}
else
{
headerPart = enc_header;
headerPart2 = br.ReadBytes(0x800);
}
//Get crypto_type for master_key
var cryptoType = (headerPart[0x220] > headerPart[0x206]) ? headerPart[0x220] : headerPart[0x206];
if (cryptoType == 1)
{
cryptoType--;
}
//RightsID
bool hasRightsID = false;
for (int i = 0; i < 0x10; i++)
{
if (headerPart[0x230 + i] != 0)
{
hasRightsID = true;
break;
}
}
/* Explanation:
* - if a RightsID is set, an external titleKey is needed. This titleKey is contained in a ticket,
* most likely installed on the system by download titles from eshop
* - if no RightsID is set, the nca internal keyarea is used to decrypt the contents
*/
byte[] dec_title_key = null;
byte[] dec_key_area = null;
if (!hasRightsID)
{
//Decrypt keyarea
var keyIndex = headerPart[0x207];
if (keyIndex > 2)
{
throw new InvalidDataException($"NCA KeyIndex must be 0-2. Found KeyIndex: {keyIndex}");
}
dec_key_area = Decryption.ECB128(headerPart.GetElements(0x300, 0x40), keyset.keyAreaKeys[cryptoType][keyIndex]);
}
else
{
//Decrypt title_key
var title_key = InputBox.Show("Input Titlekey:", "Decrypt NCA").Hexlify(16);
dec_title_key = Decryption.ECB128(title_key, keyset.titleKeks[cryptoType]);
}
//Read out section crypto
List <SectionEntry> sectionList = new BinaryReaderX(new MemoryStream(headerPart.GetElements(0x240, 0x40))).ReadMultiple <SectionEntry>(4);
for (int i = 0; i < 4; i++)
{
if (sectionList[i].mediaOffset != 0 && sectionList[i].endMediaOffset != 0)
{
br.BaseStream.Position = offset + sectionList[i].mediaOffset * 0x200;
if (hasRightsID)
{
var enc_buffer = br.ReadBytes(sectionList[i].endMediaOffset * 0x200 - sectionList[i].mediaOffset * 0x200);
var dec_buffer = Decryption.CTR128(enc_buffer, dec_title_key, GenerateCTR(i + 1, sectionList[i].mediaOffset * 0x200));
bw.BaseStream.Position = offset + sectionList[i].mediaOffset * 0x200;
bw.Write(dec_buffer);
}
else
{
var sectionCrypto = headerPart2[i * 0x200 + 0x4];
if (sectionCrypto == 0 || sectionCrypto > 4)
{
throw new InvalidDataException($"SectionCrypto {i} must be 1-4. Found SectionCrypto: {sectionCrypto}");
}
switch (sectionCrypto)
{
//case 1 is NoCrypto
case 2:
//XTS
var enc_buffer = br.ReadBytes(sectionList[i].endMediaOffset * 0x200 - sectionList[i].mediaOffset * 0x200);
var dec_buffer = Decryption.XTS128(enc_buffer, dec_key_area.GetElements(0, 0x20), 0x200);
bw.BaseStream.Position = offset + sectionList[i].mediaOffset * 0x200;
bw.Write(dec_buffer);
break;
case 3:
//CTR
enc_buffer = br.ReadBytes(sectionList[i].endMediaOffset * 0x200 - sectionList[i].mediaOffset * 0x200);
dec_buffer = Decryption.CTR128(enc_buffer, dec_key_area.GetElements(0x20, 0x10), GenerateCTR(i + 1, sectionList[i].mediaOffset * 0x200));
bw.BaseStream.Position = offset + sectionList[i].mediaOffset * 0x200;
bw.Write(dec_buffer);
break;
case 4:
//BKTR
//stub
break;
}
bw.BaseStream.Position = offset + 0x400 + i * 0x200 + 0x4;
bw.Write((byte)0x1);
}
}
}
}
}
