suyu/src/core/hle/service/nfp/amiibo_crypto.cpp

// SPDX-FileCopyrightText: Copyright 2022 yuzu Emulator Project
// SPDX-License-Identifier: GPL-3.0-or-later

// SPDX-FileCopyrightText: Copyright 2017 socram8888/amiitool
// SPDX-License-Identifier: MIT

#include <array>
#include <mbedtls/aes.h>
#include <mbedtls/hmac_drbg.h>

#include "common/fs/file.h"
#include "common/fs/path_util.h"
#include "common/logging/log.h"
#include "core/hle/service/mii/mii_manager.h"
#include "core/hle/service/nfp/amiibo_crypto.h"

namespace Service::NFP::AmiiboCrypto {

bool IsAmiiboValid(const EncryptedNTAG215File& ntag_file) {
    const auto& amiibo_data = ntag_file.user_memory;
    LOG_DEBUG(Service_NFP, "uuid_lock=0x{0:x}", ntag_file.static_lock);
    LOG_DEBUG(Service_NFP, "compability_container=0x{0:x}", ntag_file.compability_container);
    LOG_INFO(Service_NFP, "write_count={}", amiibo_data.write_counter);

    LOG_INFO(Service_NFP, "character_id=0x{0:x}", amiibo_data.model_info.character_id);
    LOG_INFO(Service_NFP, "character_variant={}", amiibo_data.model_info.character_variant);
    LOG_INFO(Service_NFP, "amiibo_type={}", amiibo_data.model_info.amiibo_type);
    LOG_INFO(Service_NFP, "model_number=0x{0:x}", amiibo_data.model_info.model_number);
    LOG_INFO(Service_NFP, "series={}", amiibo_data.model_info.series);
    LOG_DEBUG(Service_NFP, "fixed_value=0x{0:x}", amiibo_data.model_info.constant_value);

    LOG_DEBUG(Service_NFP, "tag_dynamic_lock=0x{0:x}", ntag_file.dynamic_lock);
    LOG_DEBUG(Service_NFP, "tag_CFG0=0x{0:x}", ntag_file.CFG0);
    LOG_DEBUG(Service_NFP, "tag_CFG1=0x{0:x}", ntag_file.CFG1);

    // Validate UUID
    constexpr u8 CT = 0x88; // As defined in `ISO / IEC 14443 - 3`
    if ((CT ^ ntag_file.uuid[0] ^ ntag_file.uuid[1] ^ ntag_file.uuid[2]) != ntag_file.uuid[3]) {
        return false;
    }
    if ((ntag_file.uuid[4] ^ ntag_file.uuid[5] ^ ntag_file.uuid[6] ^ ntag_file.uuid[7]) !=
        ntag_file.uuid[8]) {
        return false;
    }

    // Check against all know constants on an amiibo binary
    if (ntag_file.static_lock != 0xE00F) {
        return false;
    }
    if (ntag_file.compability_container != 0xEEFF10F1U) {
        return false;
    }
    if (amiibo_data.constant_value != 0xA5) {
        return false;
    }
    if (amiibo_data.model_info.constant_value != 0x02) {
        return false;
    }
    // dynamic_lock value apparently is not constant
    // ntag_file.dynamic_lock == 0x0F0001
    if (ntag_file.CFG0 != 0x04000000U) {
        return false;
    }
    if (ntag_file.CFG1 != 0x5F) {
        return false;
    }
    return true;
}

NTAG215File NfcDataToEncodedData(const EncryptedNTAG215File& nfc_data) {
    NTAG215File encoded_data{};

    memcpy(encoded_data.uuid2.data(), nfc_data.uuid.data() + 0x8, sizeof(encoded_data.uuid2));
    encoded_data.static_lock = nfc_data.static_lock;
    encoded_data.compability_container = nfc_data.compability_container;
    encoded_data.hmac_data = nfc_data.user_memory.hmac_data;
    encoded_data.constant_value = nfc_data.user_memory.constant_value;
    encoded_data.write_counter = nfc_data.user_memory.write_counter;
    encoded_data.settings = nfc_data.user_memory.settings;
    encoded_data.owner_mii = nfc_data.user_memory.owner_mii;
    encoded_data.title_id = nfc_data.user_memory.title_id;
    encoded_data.applicaton_write_counter = nfc_data.user_memory.applicaton_write_counter;
    encoded_data.application_area_id = nfc_data.user_memory.application_area_id;
    encoded_data.unknown = nfc_data.user_memory.unknown;
    encoded_data.hash = nfc_data.user_memory.hash;
    encoded_data.application_area = nfc_data.user_memory.application_area;
    encoded_data.hmac_tag = nfc_data.user_memory.hmac_tag;
    memcpy(encoded_data.uuid.data(), nfc_data.uuid.data(), sizeof(encoded_data.uuid));
    encoded_data.model_info = nfc_data.user_memory.model_info;
    encoded_data.keygen_salt = nfc_data.user_memory.keygen_salt;
    encoded_data.dynamic_lock = nfc_data.dynamic_lock;
    encoded_data.CFG0 = nfc_data.CFG0;
    encoded_data.CFG1 = nfc_data.CFG1;
    encoded_data.password = nfc_data.password;

    return encoded_data;
}

EncryptedNTAG215File EncodedDataToNfcData(const NTAG215File& encoded_data) {
    EncryptedNTAG215File nfc_data{};

    memcpy(nfc_data.uuid.data() + 0x8, encoded_data.uuid2.data(), sizeof(encoded_data.uuid2));
    memcpy(nfc_data.uuid.data(), encoded_data.uuid.data(), sizeof(encoded_data.uuid));
    nfc_data.static_lock = encoded_data.static_lock;
    nfc_data.compability_container = encoded_data.compability_container;
    nfc_data.user_memory.hmac_data = encoded_data.hmac_data;
    nfc_data.user_memory.constant_value = encoded_data.constant_value;
    nfc_data.user_memory.write_counter = encoded_data.write_counter;
    nfc_data.user_memory.settings = encoded_data.settings;
    nfc_data.user_memory.owner_mii = encoded_data.owner_mii;
    nfc_data.user_memory.title_id = encoded_data.title_id;
    nfc_data.user_memory.applicaton_write_counter = encoded_data.applicaton_write_counter;
    nfc_data.user_memory.application_area_id = encoded_data.application_area_id;
    nfc_data.user_memory.unknown = encoded_data.unknown;
    nfc_data.user_memory.hash = encoded_data.hash;
    nfc_data.user_memory.application_area = encoded_data.application_area;
    nfc_data.user_memory.hmac_tag = encoded_data.hmac_tag;
    nfc_data.user_memory.model_info = encoded_data.model_info;
    nfc_data.user_memory.keygen_salt = encoded_data.keygen_salt;
    nfc_data.dynamic_lock = encoded_data.dynamic_lock;
    nfc_data.CFG0 = encoded_data.CFG0;
    nfc_data.CFG1 = encoded_data.CFG1;
    nfc_data.password = encoded_data.password;

    return nfc_data;
}

u32 GetTagPassword(const TagUuid& uuid) {
    // Verifiy that the generated password is correct
    u32 password = 0xAA ^ (uuid[1] ^ uuid[3]);
    password &= (0x55 ^ (uuid[2] ^ uuid[4])) << 8;
    password &= (0xAA ^ (uuid[3] ^ uuid[5])) << 16;
    password &= (0x55 ^ (uuid[4] ^ uuid[6])) << 24;
    return password;
}

HashSeed GetSeed(const NTAG215File& data) {
    HashSeed seed{
        .magic = data.write_counter,
        .padding = {},
        .uuid1 = {},
        .uuid2 = {},
        .keygen_salt = data.keygen_salt,
    };

    // Copy the first 8 bytes of uuid
    memcpy(seed.uuid1.data(), data.uuid.data(), sizeof(seed.uuid1));
    memcpy(seed.uuid2.data(), data.uuid.data(), sizeof(seed.uuid2));

    return seed;
}

std::vector<u8> GenerateInternalKey(const InternalKey& key, const HashSeed& seed) {
    const std::size_t seedPart1Len = sizeof(key.magic_bytes) - key.magic_length;
    const std::size_t string_size = key.type_string.size();
    std::vector<u8> output(string_size + seedPart1Len);

    // Copy whole type string
    memccpy(output.data(), key.type_string.data(), '\0', string_size);

    // Append (16 - magic_length) from the input seed
    memcpy(output.data() + string_size, &seed, seedPart1Len);

    // Append all bytes from magicBytes
    output.insert(output.end(), key.magic_bytes.begin(),
                  key.magic_bytes.begin() + key.magic_length);

    output.insert(output.end(), seed.uuid1.begin(), seed.uuid1.end());
    output.insert(output.end(), seed.uuid2.begin(), seed.uuid2.end());

    for (std::size_t i = 0; i < sizeof(seed.keygen_salt); i++) {
        output.emplace_back(static_cast<u8>(seed.keygen_salt[i] ^ key.xor_pad[i]));
    }

    return output;
}

void CryptoInit(CryptoCtx& ctx, mbedtls_md_context_t& hmac_ctx, const HmacKey& hmac_key,
                const std::vector<u8>& seed) {

    // Initialize context
    ctx.used = false;
    ctx.counter = 0;
    ctx.buffer_size = sizeof(ctx.counter) + seed.size();
    memcpy(ctx.buffer.data() + sizeof(u16), seed.data(), seed.size());

    // Initialize HMAC context
    mbedtls_md_init(&hmac_ctx);
    mbedtls_md_setup(&hmac_ctx, mbedtls_md_info_from_type(MBEDTLS_MD_SHA256), 1);
    mbedtls_md_hmac_starts(&hmac_ctx, hmac_key.data(), hmac_key.size());
}

void CryptoStep(CryptoCtx& ctx, mbedtls_md_context_t& hmac_ctx, DrgbOutput& output) {
    // If used at least once, reinitialize the HMAC
    if (ctx.used) {
        mbedtls_md_hmac_reset(&hmac_ctx);
    }

    ctx.used = true;

    // Store counter in big endian, and increment it
    ctx.buffer[0] = static_cast<u8>(ctx.counter >> 8);
    ctx.buffer[1] = static_cast<u8>(ctx.counter >> 0);
    ctx.counter++;

    // Do HMAC magic
    mbedtls_md_hmac_update(&hmac_ctx, reinterpret_cast<const unsigned char*>(ctx.buffer.data()),
                           ctx.buffer_size);
    mbedtls_md_hmac_finish(&hmac_ctx, output.data());
}

DerivedKeys GenerateKey(const InternalKey& key, const NTAG215File& data) {
    const auto seed = GetSeed(data);

    // Generate internal seed
    const std::vector<u8> internal_key = GenerateInternalKey(key, seed);

    // Initialize context
    CryptoCtx ctx{};
    mbedtls_md_context_t hmac_ctx;
    CryptoInit(ctx, hmac_ctx, key.hmac_key, internal_key);

    // Generate derived keys
    DerivedKeys derived_keys{};
    std::array<DrgbOutput, 2> temp{};
    CryptoStep(ctx, hmac_ctx, temp[0]);
    CryptoStep(ctx, hmac_ctx, temp[1]);
    memcpy(&derived_keys, temp.data(), sizeof(DerivedKeys));

    // Cleanup context
    mbedtls_md_free(&hmac_ctx);

    return derived_keys;
}

void Cipher(const DerivedKeys& keys, const NTAG215File& in_data, NTAG215File& out_data) {
    mbedtls_aes_context aes;
    std::size_t nc_off = 0;
    std::array<u8, sizeof(keys.aes_iv)> nonce_counter{};
    std::array<u8, sizeof(keys.aes_iv)> stream_block{};

    const auto aes_key_size = static_cast<u32>(keys.aes_key.size() * 8);
    mbedtls_aes_setkey_enc(&aes, keys.aes_key.data(), aes_key_size);
    memcpy(nonce_counter.data(), keys.aes_iv.data(), sizeof(keys.aes_iv));

    constexpr std::size_t encrypted_data_size = HMAC_TAG_START - SETTINGS_START;
    mbedtls_aes_crypt_ctr(&aes, encrypted_data_size, &nc_off, nonce_counter.data(),
                          stream_block.data(),
                          reinterpret_cast<const unsigned char*>(&in_data.settings),
                          reinterpret_cast<unsigned char*>(&out_data.settings));

    // Copy the rest of the data directly
    out_data.uuid2 = in_data.uuid2;
    out_data.static_lock = in_data.static_lock;
    out_data.compability_container = in_data.compability_container;

    out_data.constant_value = in_data.constant_value;
    out_data.write_counter = in_data.write_counter;

    out_data.uuid = in_data.uuid;
    out_data.model_info = in_data.model_info;
    out_data.keygen_salt = in_data.keygen_salt;
    out_data.dynamic_lock = in_data.dynamic_lock;
    out_data.CFG0 = in_data.CFG0;
    out_data.CFG1 = in_data.CFG1;
    out_data.password = in_data.password;
}

bool LoadKeys(InternalKey& locked_secret, InternalKey& unfixed_info) {
    const auto yuzu_keys_dir = Common::FS::GetYuzuPath(Common::FS::YuzuPath::KeysDir);

    const Common::FS::IOFile keys_file{yuzu_keys_dir / "key_retail.bin",
                                       Common::FS::FileAccessMode::Read,
                                       Common::FS::FileType::BinaryFile};

    if (!keys_file.IsOpen()) {
        LOG_ERROR(Service_NFP, "No keys detected");
        return false;
    }

    if (keys_file.Read(unfixed_info) != 1) {
        LOG_ERROR(Service_NFP, "Failed to read unfixed_info");
        return false;
    }
    if (keys_file.Read(locked_secret) != 1) {
        LOG_ERROR(Service_NFP, "Failed to read locked-secret");
        return false;
    }

    return true;
}

bool DecodeAmiibo(const EncryptedNTAG215File& encrypted_tag_data, NTAG215File& tag_data) {
    InternalKey locked_secret{};
    InternalKey unfixed_info{};

    if (!LoadKeys(locked_secret, unfixed_info)) {
        return false;
    }

    // Generate keys
    NTAG215File encoded_data = NfcDataToEncodedData(encrypted_tag_data);
    const auto data_keys = GenerateKey(unfixed_info, encoded_data);
    const auto tag_keys = GenerateKey(locked_secret, encoded_data);

    // Decrypt
    Cipher(data_keys, encoded_data, tag_data);

    // Regenerate tag HMAC. Note: order matters, data HMAC depends on tag HMAC!
    constexpr std::size_t input_length = DYNAMIC_LOCK_START - UUID_START;
    mbedtls_md_hmac(mbedtls_md_info_from_type(MBEDTLS_MD_SHA256), tag_keys.hmac_key.data(),
                    sizeof(HmacKey), reinterpret_cast<const unsigned char*>(&tag_data.uuid),
                    input_length, reinterpret_cast<unsigned char*>(&tag_data.hmac_tag));

    // Regenerate data HMAC
    constexpr std::size_t input_length2 = DYNAMIC_LOCK_START - WRITE_COUNTER_START;
    mbedtls_md_hmac(mbedtls_md_info_from_type(MBEDTLS_MD_SHA256), data_keys.hmac_key.data(),
                    sizeof(HmacKey),
                    reinterpret_cast<const unsigned char*>(&tag_data.write_counter), input_length2,
                    reinterpret_cast<unsigned char*>(&tag_data.hmac_data));

    if (tag_data.hmac_data != encrypted_tag_data.user_memory.hmac_data) {
        LOG_ERROR(Service_NFP, "hmac_data doesn't match");
        return false;
    }

    if (tag_data.hmac_tag != encrypted_tag_data.user_memory.hmac_tag) {
        LOG_ERROR(Service_NFP, "hmac_tag doesn't match");
        return false;
    }

    return true;
}

bool EncodeAmiibo(const NTAG215File& tag_data, EncryptedNTAG215File& encrypted_tag_data) {
    InternalKey locked_secret{};
    InternalKey unfixed_info{};

    if (!LoadKeys(locked_secret, unfixed_info)) {
        return false;
    }

    // Generate keys
    const auto data_keys = GenerateKey(unfixed_info, tag_data);
    const auto tag_keys = GenerateKey(locked_secret, tag_data);

    NTAG215File encoded_tag_data{};

    // Generate tag HMAC
    constexpr std::size_t input_length = DYNAMIC_LOCK_START - UUID_START;
    constexpr std::size_t input_length2 = HMAC_TAG_START - WRITE_COUNTER_START;
    mbedtls_md_hmac(mbedtls_md_info_from_type(MBEDTLS_MD_SHA256), tag_keys.hmac_key.data(),
                    sizeof(HmacKey), reinterpret_cast<const unsigned char*>(&tag_data.uuid),
                    input_length, reinterpret_cast<unsigned char*>(&encoded_tag_data.hmac_tag));

    // Init mbedtls HMAC context
    mbedtls_md_context_t ctx;
    mbedtls_md_init(&ctx);
    mbedtls_md_setup(&ctx, mbedtls_md_info_from_type(MBEDTLS_MD_SHA256), 1);

    // Generate data HMAC
    mbedtls_md_hmac_starts(&ctx, data_keys.hmac_key.data(), sizeof(HmacKey));
    mbedtls_md_hmac_update(&ctx, reinterpret_cast<const unsigned char*>(&tag_data.write_counter),
                           input_length2); // Data
    mbedtls_md_hmac_update(&ctx, reinterpret_cast<unsigned char*>(&encoded_tag_data.hmac_tag),
                           sizeof(HashData)); // Tag HMAC
    mbedtls_md_hmac_update(&ctx, reinterpret_cast<const unsigned char*>(&tag_data.uuid),
                           input_length);
    mbedtls_md_hmac_finish(&ctx, reinterpret_cast<unsigned char*>(&encoded_tag_data.hmac_data));

    // HMAC cleanup
    mbedtls_md_free(&ctx);

    // Encrypt
    Cipher(data_keys, tag_data, encoded_tag_data);

    // Convert back to hardware
    encrypted_tag_data = EncodedDataToNfcData(encoded_tag_data);

    return true;
}

} // namespace Service::NFP::AmiiboCrypto