unleashed-firmware/applications/main/u2f/u2f_data.c

#include <furi.h>
#include "u2f_data.h"
#include <furi_hal.h>
#include <storage/storage.h>
#include <furi_hal_random.h>
#include <flipper_format/flipper_format.h>

#define TAG "U2F"

#define U2F_DATA_FOLDER ANY_PATH("u2f/")
#define U2F_CERT_FILE U2F_DATA_FOLDER "assets/cert.der"
#define U2F_CERT_KEY_FILE U2F_DATA_FOLDER "assets/cert_key.u2f"
#define U2F_KEY_FILE U2F_DATA_FOLDER "key.u2f"
#define U2F_CNT_FILE U2F_DATA_FOLDER "cnt.u2f"

#define U2F_DATA_FILE_ENCRYPTION_KEY_SLOT_FACTORY 2
#define U2F_DATA_FILE_ENCRYPTION_KEY_SLOT_UNIQUE 11

#define U2F_CERT_STOCK 0 // Stock certificate, private key is encrypted with factory key
#define U2F_CERT_USER 1 // User certificate, private key is encrypted with unique key
#define U2F_CERT_USER_UNENCRYPTED \
    2 // Unencrypted user certificate, will be encrypted after first load

#define U2F_CERT_KEY_FILE_TYPE "Flipper U2F Certificate Key File"
#define U2F_CERT_KEY_VERSION 1

#define U2F_DEVICE_KEY_FILE_TYPE "Flipper U2F Device Key File"
#define U2F_DEVICE_KEY_VERSION 1

#define U2F_COUNTER_FILE_TYPE "Flipper U2F Counter File"
#define U2F_COUNTER_VERSION 2
#define U2F_COUNTER_VERSION_OLD 1

#define U2F_COUNTER_CONTROL_VAL 0xAA5500FF

typedef struct {
    uint32_t counter;
    uint8_t random_salt[24];
    uint32_t control;
} __attribute__((packed)) U2fCounterData;

bool u2f_data_check(bool cert_only) {
    bool state = false;
    Storage* fs_api = furi_record_open(RECORD_STORAGE);
    File* file = storage_file_alloc(fs_api);

    do {
        if(!storage_file_open(file, U2F_CERT_FILE, FSAM_READ, FSOM_OPEN_EXISTING)) break;
        storage_file_close(file);
        if(!storage_file_open(file, U2F_CERT_KEY_FILE, FSAM_READ, FSOM_OPEN_EXISTING)) break;
        if(cert_only) {
            state = true;
            break;
        }
        storage_file_close(file);
        if(!storage_file_open(file, U2F_KEY_FILE, FSAM_READ, FSOM_OPEN_EXISTING)) break;
        storage_file_close(file);
        if(!storage_file_open(file, U2F_CNT_FILE, FSAM_READ, FSOM_OPEN_EXISTING)) break;
        state = true;
    } while(0);

    storage_file_close(file);
    storage_file_free(file);

    furi_record_close(RECORD_STORAGE);

    return state;
}

bool u2f_data_cert_check() {
    bool state = false;
    Storage* fs_api = furi_record_open(RECORD_STORAGE);
    File* file = storage_file_alloc(fs_api);
    uint8_t file_buf[8];

    if(storage_file_open(file, U2F_CERT_FILE, FSAM_READ, FSOM_OPEN_EXISTING)) {
        do {
            // Read header to check certificate size
            size_t file_size = storage_file_size(file);
            size_t len_cur = storage_file_read(file, file_buf, 4);
            if(len_cur != 4) break;

            if(file_buf[0] != 0x30) {
                FURI_LOG_E(TAG, "Wrong certificate header");
                break;
            }

            size_t temp_len = ((file_buf[2] << 8) | (file_buf[3])) + 4;
            if(temp_len != file_size) {
                FURI_LOG_E(TAG, "Wrong certificate length");
                break;
            }
            state = true;
        } while(0);
    }

    storage_file_close(file);
    storage_file_free(file);

    furi_record_close(RECORD_STORAGE);

    return state;
}

uint32_t u2f_data_cert_load(uint8_t* cert) {
    furi_assert(cert);

    Storage* fs_api = furi_record_open(RECORD_STORAGE);
    File* file = storage_file_alloc(fs_api);
    uint32_t file_size = 0;
    uint32_t len_cur = 0;

    if(storage_file_open(file, U2F_CERT_FILE, FSAM_READ, FSOM_OPEN_EXISTING)) {
        file_size = storage_file_size(file);
        len_cur = storage_file_read(file, cert, file_size);
        if(len_cur != file_size) len_cur = 0;
    }

    storage_file_close(file);
    storage_file_free(file);
    furi_record_close(RECORD_STORAGE);

    return len_cur;
}

static bool u2f_data_cert_key_encrypt(uint8_t* cert_key) {
    furi_assert(cert_key);

    bool state = false;
    uint8_t iv[16];
    uint8_t key[48];
    uint32_t cert_type = U2F_CERT_USER;

    FURI_LOG_I(TAG, "Encrypting user cert key");

    // Generate random IV
    furi_hal_random_fill_buf(iv, 16);

    if(!furi_hal_crypto_store_load_key(U2F_DATA_FILE_ENCRYPTION_KEY_SLOT_UNIQUE, iv)) {
        FURI_LOG_E(TAG, "Unable to load encryption key");
        return false;
    }

    if(!furi_hal_crypto_encrypt(cert_key, key, 32)) {
        FURI_LOG_E(TAG, "Encryption failed");
        return false;
    }
    furi_hal_crypto_store_unload_key(U2F_DATA_FILE_ENCRYPTION_KEY_SLOT_UNIQUE);

    Storage* storage = furi_record_open(RECORD_STORAGE);
    FlipperFormat* flipper_format = flipper_format_file_alloc(storage);

    if(flipper_format_file_open_always(flipper_format, U2F_CERT_KEY_FILE)) {
        do {
            if(!flipper_format_write_header_cstr(
                   flipper_format, U2F_CERT_KEY_FILE_TYPE, U2F_CERT_KEY_VERSION))
                break;
            if(!flipper_format_write_uint32(flipper_format, "Type", &cert_type, 1)) break;
            if(!flipper_format_write_hex(flipper_format, "IV", iv, 16)) break;
            if(!flipper_format_write_hex(flipper_format, "Data", key, 48)) break;
            state = true;
        } while(0);
    }

    flipper_format_free(flipper_format);
    furi_record_close(RECORD_STORAGE);

    return state;
}

bool u2f_data_cert_key_load(uint8_t* cert_key) {
    furi_assert(cert_key);

    bool state = false;
    uint8_t iv[16];
    uint8_t key[48];
    uint32_t cert_type = 0;
    uint8_t key_slot = 0;
    uint32_t version = 0;

    // Check if unique key exists in secure eclave and generate it if missing
    if(!furi_hal_crypto_verify_key(U2F_DATA_FILE_ENCRYPTION_KEY_SLOT_UNIQUE)) return false;

    FuriString* filetype;
    filetype = furi_string_alloc();

    Storage* storage = furi_record_open(RECORD_STORAGE);
    FlipperFormat* flipper_format = flipper_format_file_alloc(storage);

    if(flipper_format_file_open_existing(flipper_format, U2F_CERT_KEY_FILE)) {
        do {
            if(!flipper_format_read_header(flipper_format, filetype, &version)) {
                FURI_LOG_E(TAG, "Missing or incorrect header");
                break;
            }

            if(strcmp(furi_string_get_cstr(filetype), U2F_CERT_KEY_FILE_TYPE) != 0 ||
               version != U2F_CERT_KEY_VERSION) {
                FURI_LOG_E(TAG, "Type or version mismatch");
                break;
            }

            if(!flipper_format_read_uint32(flipper_format, "Type", &cert_type, 1)) {
                FURI_LOG_E(TAG, "Missing cert type");
                break;
            }

            if(cert_type == U2F_CERT_STOCK) {
                key_slot = U2F_DATA_FILE_ENCRYPTION_KEY_SLOT_FACTORY;
            } else if(cert_type == U2F_CERT_USER) {
                key_slot = U2F_DATA_FILE_ENCRYPTION_KEY_SLOT_UNIQUE;
            } else if(cert_type == U2F_CERT_USER_UNENCRYPTED) {
                key_slot = 0;
            } else {
                FURI_LOG_E(TAG, "Unknown cert type");
                break;
            }
            if(key_slot != 0) {
                if(!flipper_format_read_hex(flipper_format, "IV", iv, 16)) {
                    FURI_LOG_E(TAG, "Missing IV");
                    break;
                }

                if(!flipper_format_read_hex(flipper_format, "Data", key, 48)) {
                    FURI_LOG_E(TAG, "Missing data");
                    break;
                }

                if(!furi_hal_crypto_store_load_key(key_slot, iv)) {
                    FURI_LOG_E(TAG, "Unable to load encryption key");
                    break;
                }
                memset(cert_key, 0, 32);

                if(!furi_hal_crypto_decrypt(key, cert_key, 32)) {
                    memset(cert_key, 0, 32);
                    FURI_LOG_E(TAG, "Decryption failed");
                    break;
                }
                furi_hal_crypto_store_unload_key(key_slot);
            } else {
                if(!flipper_format_read_hex(flipper_format, "Data", cert_key, 32)) {
                    FURI_LOG_E(TAG, "Missing data");
                    break;
                }
            }
            state = true;
        } while(0);
    }

    flipper_format_free(flipper_format);
    furi_record_close(RECORD_STORAGE);
    furi_string_free(filetype);

    if(cert_type == U2F_CERT_USER_UNENCRYPTED) {
        return u2f_data_cert_key_encrypt(cert_key);
    }

    return state;
}

bool u2f_data_key_load(uint8_t* device_key) {
    furi_assert(device_key);

    bool state = false;
    uint8_t iv[16];
    uint8_t key[48];
    uint32_t version = 0;

    FuriString* filetype;
    filetype = furi_string_alloc();

    Storage* storage = furi_record_open(RECORD_STORAGE);
    FlipperFormat* flipper_format = flipper_format_file_alloc(storage);

    if(flipper_format_file_open_existing(flipper_format, U2F_KEY_FILE)) {
        do {
            if(!flipper_format_read_header(flipper_format, filetype, &version)) {
                FURI_LOG_E(TAG, "Missing or incorrect header");
                break;
            }
            if(strcmp(furi_string_get_cstr(filetype), U2F_DEVICE_KEY_FILE_TYPE) != 0 ||
               version != U2F_DEVICE_KEY_VERSION) {
                FURI_LOG_E(TAG, "Type or version mismatch");
                break;
            }
            if(!flipper_format_read_hex(flipper_format, "IV", iv, 16)) {
                FURI_LOG_E(TAG, "Missing IV");
                break;
            }
            if(!flipper_format_read_hex(flipper_format, "Data", key, 48)) {
                FURI_LOG_E(TAG, "Missing data");
                break;
            }
            if(!furi_hal_crypto_store_load_key(U2F_DATA_FILE_ENCRYPTION_KEY_SLOT_UNIQUE, iv)) {
                FURI_LOG_E(TAG, "Unable to load encryption key");
                break;
            }
            memset(device_key, 0, 32);
            if(!furi_hal_crypto_decrypt(key, device_key, 32)) {
                memset(device_key, 0, 32);
                FURI_LOG_E(TAG, "Decryption failed");
                break;
            }
            furi_hal_crypto_store_unload_key(U2F_DATA_FILE_ENCRYPTION_KEY_SLOT_UNIQUE);
            state = true;
        } while(0);
    }
    flipper_format_free(flipper_format);
    furi_record_close(RECORD_STORAGE);
    furi_string_free(filetype);
    return state;
}

bool u2f_data_key_generate(uint8_t* device_key) {
    furi_assert(device_key);

    bool state = false;
    uint8_t iv[16];
    uint8_t key[32];
    uint8_t key_encrypted[48];

    // Generate random IV and key
    furi_hal_random_fill_buf(iv, 16);
    furi_hal_random_fill_buf(key, 32);

    if(!furi_hal_crypto_store_load_key(U2F_DATA_FILE_ENCRYPTION_KEY_SLOT_UNIQUE, iv)) {
        FURI_LOG_E(TAG, "Unable to load encryption key");
        return false;
    }

    if(!furi_hal_crypto_encrypt(key, key_encrypted, 32)) {
        FURI_LOG_E(TAG, "Encryption failed");
        return false;
    }
    furi_hal_crypto_store_unload_key(U2F_DATA_FILE_ENCRYPTION_KEY_SLOT_UNIQUE);

    Storage* storage = furi_record_open(RECORD_STORAGE);
    FlipperFormat* flipper_format = flipper_format_file_alloc(storage);

    if(flipper_format_file_open_always(flipper_format, U2F_KEY_FILE)) {
        do {
            if(!flipper_format_write_header_cstr(
                   flipper_format, U2F_DEVICE_KEY_FILE_TYPE, U2F_DEVICE_KEY_VERSION))
                break;
            if(!flipper_format_write_hex(flipper_format, "IV", iv, 16)) break;
            if(!flipper_format_write_hex(flipper_format, "Data", key_encrypted, 48)) break;
            state = true;
            memcpy(device_key, key, 32);
        } while(0);
    }

    flipper_format_free(flipper_format);
    furi_record_close(RECORD_STORAGE);

    return state;
}

bool u2f_data_cnt_read(uint32_t* cnt_val) {
    furi_assert(cnt_val);

    bool state = false;
    bool old_counter = false;
    uint8_t iv[16];
    U2fCounterData cnt;
    uint8_t cnt_encr[48];
    uint32_t version = 0;

    FuriString* filetype;
    filetype = furi_string_alloc();

    Storage* storage = furi_record_open(RECORD_STORAGE);
    FlipperFormat* flipper_format = flipper_format_file_alloc(storage);

    if(flipper_format_file_open_existing(flipper_format, U2F_CNT_FILE)) {
        do {
            if(!flipper_format_read_header(flipper_format, filetype, &version)) {
                FURI_LOG_E(TAG, "Missing or incorrect header");
                break;
            }
            if(strcmp(furi_string_get_cstr(filetype), U2F_COUNTER_FILE_TYPE) != 0) {
                FURI_LOG_E(TAG, "Type mismatch");
                break;
            }
            if(version == U2F_COUNTER_VERSION_OLD) {
                // Counter is from previous U2F app version with endianness bug
                FURI_LOG_W(TAG, "Counter from old version");
                old_counter = true;
            } else if(version != U2F_COUNTER_VERSION) {
                FURI_LOG_E(TAG, "Version mismatch");
                break;
            }
            if(!flipper_format_read_hex(flipper_format, "IV", iv, 16)) {
                FURI_LOG_E(TAG, "Missing IV");
                break;
            }
            if(!flipper_format_read_hex(flipper_format, "Data", cnt_encr, 48)) {
                FURI_LOG_E(TAG, "Missing data");
                break;
            }
            if(!furi_hal_crypto_store_load_key(U2F_DATA_FILE_ENCRYPTION_KEY_SLOT_UNIQUE, iv)) {
                FURI_LOG_E(TAG, "Unable to load encryption key");
                break;
            }
            memset(&cnt, 0, sizeof(U2fCounterData));
            if(!furi_hal_crypto_decrypt(cnt_encr, (uint8_t*)&cnt, sizeof(U2fCounterData))) {
                memset(&cnt, 0, sizeof(U2fCounterData));
                FURI_LOG_E(TAG, "Decryption failed");
                break;
            }
            furi_hal_crypto_store_unload_key(U2F_DATA_FILE_ENCRYPTION_KEY_SLOT_UNIQUE);
            if(cnt.control == U2F_COUNTER_CONTROL_VAL) {
                *cnt_val = cnt.counter;
                state = true;
            }
        } while(0);
    }
    flipper_format_free(flipper_format);
    furi_record_close(RECORD_STORAGE);
    furi_string_free(filetype);

    if(old_counter && state) {
        // Change counter endianness and rewrite counter file
        *cnt_val = __REV(cnt.counter);
        state = u2f_data_cnt_write(*cnt_val);
    }

    return state;
}

bool u2f_data_cnt_write(uint32_t cnt_val) {
    bool state = false;
    uint8_t iv[16];
    U2fCounterData cnt;
    uint8_t cnt_encr[48];

    // Generate random IV and key
    furi_hal_random_fill_buf(iv, 16);
    furi_hal_random_fill_buf(cnt.random_salt, 24);
    cnt.control = U2F_COUNTER_CONTROL_VAL;
    cnt.counter = cnt_val;

    if(!furi_hal_crypto_store_load_key(U2F_DATA_FILE_ENCRYPTION_KEY_SLOT_UNIQUE, iv)) {
        FURI_LOG_E(TAG, "Unable to load encryption key");
        return false;
    }

    if(!furi_hal_crypto_encrypt((uint8_t*)&cnt, cnt_encr, 32)) {
        FURI_LOG_E(TAG, "Encryption failed");
        return false;
    }
    furi_hal_crypto_store_unload_key(U2F_DATA_FILE_ENCRYPTION_KEY_SLOT_UNIQUE);

    Storage* storage = furi_record_open(RECORD_STORAGE);
    FlipperFormat* flipper_format = flipper_format_file_alloc(storage);

    if(flipper_format_file_open_always(flipper_format, U2F_CNT_FILE)) {
        do {
            if(!flipper_format_write_header_cstr(
                   flipper_format, U2F_COUNTER_FILE_TYPE, U2F_COUNTER_VERSION))
                break;
            if(!flipper_format_write_hex(flipper_format, "IV", iv, 16)) break;
            if(!flipper_format_write_hex(flipper_format, "Data", cnt_encr, 48)) break;
            state = true;
        } while(0);
    }

    flipper_format_free(flipper_format);
    furi_record_close(RECORD_STORAGE);

    return state;
}