1 files changed, 56 insertions, 0 deletions

diff --git a/src/core/crypto/ctr_encryption_layer.cpp b/src/core/crypto/ctr_encryption_layer.cpp
new file mode 100644
index 000000000..106db02b3
--- /dev/null
+++ b/src/core/crypto/ctr_encryption_layer.cpp
@@ -0,0 +1,56 @@
+// Copyright 2018 yuzu emulator team
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#include <cstring>
+#include "common/assert.h"
+#include "core/crypto/ctr_encryption_layer.h"
+
+namespace Core::Crypto {
+
+CTREncryptionLayer::CTREncryptionLayer(FileSys::VirtualFile base_, Key128 key_, size_t base_offset)
+    : EncryptionLayer(std::move(base_)), base_offset(base_offset), cipher(key_, Mode::CTR),
+      iv(16, 0) {}
+
+size_t CTREncryptionLayer::Read(u8* data, size_t length, size_t offset) const {
+    if (length == 0)
+        return 0;
+
+    const auto sector_offset = offset & 0xF;
+    if (sector_offset == 0) {
+        UpdateIV(base_offset + offset);
+        std::vector<u8> raw = base->ReadBytes(length, offset);
+        if (raw.size() != length)
+            return Read(data, raw.size(), offset);
+        cipher.Transcode(raw.data(), length, data, Op::Decrypt);
+        return length;
+    }
+
+    // offset does not fall on block boundary (0x10)
+    std::vector<u8> block = base->ReadBytes(0x10, offset - sector_offset);
+    UpdateIV(base_offset + offset - sector_offset);
+    cipher.Transcode(block.data(), block.size(), block.data(), Op::Decrypt);
+    size_t read = 0x10 - sector_offset;
+
+    if (length + sector_offset < 0x10) {
+        std::memcpy(data, block.data() + sector_offset, std::min<u64>(length, read));
+        return read;
+    }
+    std::memcpy(data, block.data() + sector_offset, read);
+    return read + Read(data + read, length - read, offset + read);
+}
+
+void CTREncryptionLayer::SetIV(const std::vector<u8>& iv_) {
+    const auto length = std::min(iv_.size(), iv.size());
+    iv.assign(iv_.cbegin(), iv_.cbegin() + length);
+}
+
+void CTREncryptionLayer::UpdateIV(size_t offset) const {
+    offset >>= 4;
+    for (size_t i = 0; i < 8; ++i) {
+        iv[16 - i - 1] = offset & 0xFF;
+        offset >>= 8;
+    }
+    cipher.SetIV(iv);
+}
+} // namespace Core::Crypto