[nx] Add NcaUtils

lib/libnx/include/nx/NcaUtils.h

@@ -0,0 +1,13 @@
+#pragma once
+#include <nx/nca.h>
+
+namespace nx
+{
+	class NcaUtils
+	{
+	public:
+		static inline size_t sectorToOffset(size_t sector_index) { return sector_index * nx::nca::kSectorSize; }
+		static void decryptNcaHeader(const byte_t* src, byte_t* dst, const crypto::aes::sAesXts128Key& key);
+		static byte_t getMasterKeyRevisionFromKeyGeneration(byte_t key_generation);
+	};
+}

lib/libnx/source/NcaUtils.cpp

@@ -0,0 +1,49 @@
+#include <nx/NcaUtils.h>
+
+void nx::NcaUtils::decryptNcaHeader(const byte_t* src, byte_t* dst, const crypto::aes::sAesXts128Key& key)
+{
+	byte_t tweak[crypto::aes::kAesBlockSize];
+
+	// decrypt main header
+	byte_t raw_hdr[nx::nca::kSectorSize];
+	crypto::aes::AesXtsMakeTweak(tweak, 1);
+	crypto::aes::AesXtsDecryptSector(src + sectorToOffset(1), nx::nca::kSectorSize, key.key[0], key.key[1], tweak, raw_hdr);
+
+	bool useNca2SectorIndex = memcmp(((nx::sNcaHeader*)(raw_hdr))->signature, nx::nca::kNca2Sig.c_str(), 4) == 0;
+
+	// decrypt whole header
+	for (size_t i = 0; i < nx::nca::kHeaderSectorNum; i++)
+	{
+		crypto::aes::AesXtsMakeTweak(tweak, (i > 1 && useNca2SectorIndex)? 0 : i);
+		crypto::aes::AesXtsDecryptSector(src + sectorToOffset(i), nx::nca::kSectorSize, key.key[0], key.key[1], tweak, dst + sectorToOffset(i));
+	}
+}
+
+byte_t nx::NcaUtils::getMasterKeyRevisionFromKeyGeneration(byte_t key_generation)
+{
+	byte_t masterkey_rev;
+
+	switch (key_generation)
+	{
+		case(0):
+		case(1):
+			masterkey_rev = 0;
+			break;
+		case(2):
+			masterkey_rev = 1;
+			break;
+		case(3):
+			masterkey_rev = 2;
+			break;
+		case(4):
+			masterkey_rev = 3;
+			break;
+		case(5):
+			masterkey_rev = 4;
+			break;
+		default:
+			masterkey_rev = key_generation - 1;
+	}
+
+	return masterkey_rev;
+}