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unleashed-firmware/applications/main/u2f/u2f.c
MX 585b7f963d
Api Symbols: replace asserts with checks 
merge ofw commit
2024-03-25 13:53:32 +03:00

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#include "u2f.h"
#include "u2f_hid.h"
#include "u2f_data.h"
#include <furi.h>
#include <furi_hal.h>
#include <furi_hal_random.h>
#include <littlefs/lfs_util.h> // for lfs_tobe32
#include <mbedtls/sha256.h>
#include <mbedtls/md.h>
#include <mbedtls/ecdsa.h>
#include <mbedtls/error.h>
#define TAG "U2f"
#define WORKER_TAG TAG "Worker"
#define MCHECK(expr) furi_check((expr) == 0)
#define U2F_CMD_REGISTER 0x01
#define U2F_CMD_AUTHENTICATE 0x02
#define U2F_CMD_VERSION 0x03
typedef enum {
U2fCheckOnly = 0x07, // "check-only" - only check key handle, don't send auth response
U2fEnforce =
0x03, // "enforce-user-presence-and-sign" - send auth response only if user is present
U2fDontEnforce =
0x08, // "dont-enforce-user-presence-and-sign" - send auth response even if user is missing
} U2fAuthMode;
#define U2F_HASH_SIZE 32
#define U2F_NONCE_SIZE 32
#define U2F_CHALLENGE_SIZE 32
#define U2F_APP_ID_SIZE 32
#define U2F_EC_KEY_SIZE 32
#define U2F_EC_BIGNUM_SIZE 32
#define U2F_EC_POINT_SIZE 65
typedef struct {
uint8_t format;
uint8_t xy[64];
} FURI_PACKED U2fPubKey;
_Static_assert(sizeof(U2fPubKey) == U2F_EC_POINT_SIZE, "U2fPubKey size mismatch");
typedef struct {
uint8_t len;
uint8_t hash[U2F_HASH_SIZE];
uint8_t nonce[U2F_NONCE_SIZE];
} FURI_PACKED U2fKeyHandle;
typedef struct {
uint8_t cla;
uint8_t ins;
uint8_t p1;
uint8_t p2;
uint8_t len[3];
uint8_t challenge[U2F_CHALLENGE_SIZE];
uint8_t app_id[U2F_APP_ID_SIZE];
} FURI_PACKED U2fRegisterReq;
typedef struct {
uint8_t reserved;
U2fPubKey pub_key;
U2fKeyHandle key_handle;
uint8_t cert[];
} FURI_PACKED U2fRegisterResp;
typedef struct {
uint8_t cla;
uint8_t ins;
uint8_t p1;
uint8_t p2;
uint8_t len[3];
uint8_t challenge[U2F_CHALLENGE_SIZE];
uint8_t app_id[U2F_APP_ID_SIZE];
U2fKeyHandle key_handle;
} FURI_PACKED U2fAuthReq;
typedef struct {
uint8_t user_present;
uint32_t counter;
uint8_t signature[];
} FURI_PACKED U2fAuthResp;
static const uint8_t ver_str[] = {"U2F_V2"};
static const uint8_t state_no_error[] = {0x90, 0x00};
static const uint8_t state_not_supported[] = {0x6D, 0x00};
static const uint8_t state_user_missing[] = {0x69, 0x85};
static const uint8_t state_wrong_data[] = {0x6A, 0x80};
struct U2fData {
uint8_t device_key[U2F_EC_KEY_SIZE];
uint8_t cert_key[U2F_EC_KEY_SIZE];
uint32_t counter;
bool ready;
bool user_present;
U2fEvtCallback callback;
void* context;
mbedtls_ecp_group group;
};
static int u2f_uecc_random_cb(void* context, uint8_t* dest, unsigned size) {
UNUSED(context);
furi_hal_random_fill_buf(dest, size);
return 0;
}
U2fData* u2f_alloc(void) {
return malloc(sizeof(U2fData));
}
void u2f_free(U2fData* U2F) {
furi_assert(U2F);
mbedtls_ecp_group_free(&U2F->group);
free(U2F);
}
bool u2f_init(U2fData* U2F) {
furi_assert(U2F);
if(u2f_data_cert_check() == false) {
FURI_LOG_E(TAG, "Certificate load error");
return false;
}
if(u2f_data_cert_key_load(U2F->cert_key) == false) {
FURI_LOG_E(TAG, "Certificate key load error");
return false;
}
if(u2f_data_key_load(U2F->device_key) == false) {
FURI_LOG_W(TAG, "Key loading error, generating new");
if(u2f_data_key_generate(U2F->device_key) == false) {
FURI_LOG_E(TAG, "Key write failed");
return false;
}
}
if(u2f_data_cnt_read(&U2F->counter) == false) {
FURI_LOG_W(TAG, "Counter loading error, resetting counter");
U2F->counter = 0;
if(u2f_data_cnt_write(0) == false) {
FURI_LOG_E(TAG, "Counter write failed");
return false;
}
}
mbedtls_ecp_group_init(&U2F->group);
mbedtls_ecp_group_load(&U2F->group, MBEDTLS_ECP_DP_SECP256R1);
U2F->ready = true;
return true;
}
void u2f_set_event_callback(U2fData* U2F, U2fEvtCallback callback, void* context) {
furi_assert(U2F);
furi_assert(callback);
U2F->callback = callback;
U2F->context = context;
}
void u2f_confirm_user_present(U2fData* U2F) {
U2F->user_present = true;
}
static uint8_t u2f_der_encode_int(uint8_t* der, uint8_t* val, uint8_t val_len) {
der[0] = 0x02; // Integer
uint8_t len = 2;
// Omit leading zeros
while(val[0] == 0 && val_len > 0) {
++val;
--val_len;
}
// Check if integer is negative
if(val[0] > 0x7f) der[len++] = 0;
memcpy(der + len, val, val_len);
len += val_len;
der[1] = len - 2;
return len;
}
static uint8_t u2f_der_encode_signature(uint8_t* der, uint8_t* sig) {
der[0] = 0x30;
uint8_t len = 2;
len += u2f_der_encode_int(der + len, sig, U2F_HASH_SIZE);
len += u2f_der_encode_int(der + len, sig + U2F_HASH_SIZE, U2F_HASH_SIZE);
der[1] = len - 2;
return len;
}
static void
u2f_ecc_sign(mbedtls_ecp_group* grp, const uint8_t* key, uint8_t* hash, uint8_t* signature) {
mbedtls_mpi r, s, d;
mbedtls_mpi_init(&r);
mbedtls_mpi_init(&s);
mbedtls_mpi_init(&d);
MCHECK(mbedtls_mpi_read_binary(&d, key, U2F_EC_KEY_SIZE));
MCHECK(mbedtls_ecdsa_sign(grp, &r, &s, &d, hash, U2F_HASH_SIZE, u2f_uecc_random_cb, NULL));
MCHECK(mbedtls_mpi_write_binary(&r, signature, U2F_EC_BIGNUM_SIZE));
MCHECK(mbedtls_mpi_write_binary(&s, signature + U2F_EC_BIGNUM_SIZE, U2F_EC_BIGNUM_SIZE));
mbedtls_mpi_free(&r);
mbedtls_mpi_free(&s);
mbedtls_mpi_free(&d);
}
static void u2f_ecc_compute_public_key(
mbedtls_ecp_group* grp,
const uint8_t* private_key,
U2fPubKey* public_key) {
mbedtls_ecp_point Q;
mbedtls_mpi d;
size_t olen;
mbedtls_ecp_point_init(&Q);
mbedtls_mpi_init(&d);
MCHECK(mbedtls_mpi_read_binary(&d, private_key, U2F_EC_KEY_SIZE));
MCHECK(mbedtls_ecp_mul(grp, &Q, &d, &grp->G, u2f_uecc_random_cb, NULL));
MCHECK(mbedtls_ecp_check_privkey(grp, &d));
MCHECK(mbedtls_ecp_point_write_binary(
grp, &Q, MBEDTLS_ECP_PF_UNCOMPRESSED, &olen, (unsigned char*)public_key, sizeof(U2fPubKey)));
mbedtls_ecp_point_free(&Q);
mbedtls_mpi_free(&d);
}
///////////////////////////////////////////
static uint16_t u2f_register(U2fData* U2F, uint8_t* buf) {
U2fRegisterReq* req = (U2fRegisterReq*)buf;
U2fRegisterResp* resp = (U2fRegisterResp*)buf;
U2fKeyHandle handle;
uint8_t private[U2F_EC_KEY_SIZE];
U2fPubKey pub_key;
uint8_t hash[U2F_HASH_SIZE];
uint8_t signature[U2F_EC_BIGNUM_SIZE * 2];
if(u2f_data_check(false) == false) {
U2F->ready = false;
if(U2F->callback != NULL) U2F->callback(U2fNotifyError, U2F->context);
memcpy(&buf[0], state_not_supported, 2);
return 2;
}
if(U2F->callback != NULL) U2F->callback(U2fNotifyRegister, U2F->context);
if(U2F->user_present == false) {
memcpy(&buf[0], state_user_missing, 2);
return 2;
}
U2F->user_present = false;
handle.len = U2F_HASH_SIZE * 2;
// Generate random nonce
furi_hal_random_fill_buf(handle.nonce, 32);
{
mbedtls_md_context_t hmac_ctx;
mbedtls_md_init(&hmac_ctx);
MCHECK(mbedtls_md_setup(&hmac_ctx, mbedtls_md_info_from_type(MBEDTLS_MD_SHA256), 1));
MCHECK(mbedtls_md_hmac_starts(&hmac_ctx, U2F->device_key, sizeof(U2F->device_key)));
// Generate private key
MCHECK(mbedtls_md_hmac_update(&hmac_ctx, req->app_id, sizeof(req->app_id)));
MCHECK(mbedtls_md_hmac_update(&hmac_ctx, handle.nonce, sizeof(handle.nonce)));
MCHECK(mbedtls_md_hmac_finish(&hmac_ctx, private));
MCHECK(mbedtls_md_hmac_reset(&hmac_ctx));
// Generate private key handle
MCHECK(mbedtls_md_hmac_update(&hmac_ctx, private, sizeof(private)));
MCHECK(mbedtls_md_hmac_update(&hmac_ctx, req->app_id, sizeof(req->app_id)));
MCHECK(mbedtls_md_hmac_finish(&hmac_ctx, handle.hash));
}
// Generate public key
u2f_ecc_compute_public_key(&U2F->group, private, &pub_key);
// Generate signature
{
uint8_t reserved_byte = 0;
mbedtls_sha256_context sha_ctx;
mbedtls_sha256_init(&sha_ctx);
mbedtls_sha256_starts(&sha_ctx, 0);
mbedtls_sha256_update(&sha_ctx, &reserved_byte, 1);
mbedtls_sha256_update(&sha_ctx, req->app_id, sizeof(req->app_id));
mbedtls_sha256_update(&sha_ctx, req->challenge, sizeof(req->challenge));
mbedtls_sha256_update(&sha_ctx, handle.hash, handle.len);
mbedtls_sha256_update(&sha_ctx, (uint8_t*)&pub_key, sizeof(U2fPubKey));
mbedtls_sha256_finish(&sha_ctx, hash);
mbedtls_sha256_free(&sha_ctx);
}
// Sign hash
u2f_ecc_sign(&U2F->group, U2F->cert_key, hash, signature);
// Encode response message
resp->reserved = 0x05;
memcpy(&(resp->pub_key), &pub_key, sizeof(U2fPubKey));
memcpy(&(resp->key_handle), &handle, sizeof(U2fKeyHandle));
uint32_t cert_len = u2f_data_cert_load(resp->cert);
uint8_t signature_len = u2f_der_encode_signature(resp->cert + cert_len, signature);
memcpy(resp->cert + cert_len + signature_len, state_no_error, 2);
return (sizeof(U2fRegisterResp) + cert_len + signature_len + 2);
}
static uint16_t u2f_authenticate(U2fData* U2F, uint8_t* buf) {
U2fAuthReq* req = (U2fAuthReq*)buf;
U2fAuthResp* resp = (U2fAuthResp*)buf;
uint8_t priv_key[U2F_EC_KEY_SIZE];
uint8_t mac_control[32];
uint8_t flags = 0;
uint8_t hash[U2F_HASH_SIZE];
uint8_t signature[U2F_HASH_SIZE * 2];
uint32_t be_u2f_counter;
if(u2f_data_check(false) == false) {
U2F->ready = false;
if(U2F->callback != NULL) U2F->callback(U2fNotifyError, U2F->context);
memcpy(&buf[0], state_not_supported, 2);
return 2;
}
if(U2F->callback != NULL) U2F->callback(U2fNotifyAuth, U2F->context);
if(U2F->user_present == true) {
flags |= 1;
} else {
if(req->p1 == U2fEnforce) {
memcpy(&buf[0], state_user_missing, 2);
return 2;
}
}
U2F->user_present = false;
// The 4 byte counter is represented in big endian. Increment it before use
be_u2f_counter = lfs_tobe32(U2F->counter + 1);
// Generate hash
{
mbedtls_sha256_context sha_ctx;
mbedtls_sha256_init(&sha_ctx);
mbedtls_sha256_starts(&sha_ctx, 0);
mbedtls_sha256_update(&sha_ctx, req->app_id, sizeof(req->app_id));
mbedtls_sha256_update(&sha_ctx, &flags, 1);
mbedtls_sha256_update(&sha_ctx, (uint8_t*)&(be_u2f_counter), sizeof(be_u2f_counter));
mbedtls_sha256_update(&sha_ctx, req->challenge, sizeof(req->challenge));
mbedtls_sha256_finish(&sha_ctx, hash);
mbedtls_sha256_free(&sha_ctx);
}
{
mbedtls_md_context_t hmac_ctx;
mbedtls_md_init(&hmac_ctx);
MCHECK(mbedtls_md_setup(&hmac_ctx, mbedtls_md_info_from_type(MBEDTLS_MD_SHA256), 1));
MCHECK(mbedtls_md_hmac_starts(&hmac_ctx, U2F->device_key, sizeof(U2F->device_key)));
// Recover private key
MCHECK(mbedtls_md_hmac_update(&hmac_ctx, req->app_id, sizeof(req->app_id)));
MCHECK(mbedtls_md_hmac_update(
&hmac_ctx, req->key_handle.nonce, sizeof(req->key_handle.nonce)));
MCHECK(mbedtls_md_hmac_finish(&hmac_ctx, priv_key));
MCHECK(mbedtls_md_hmac_reset(&hmac_ctx));
// Generate and verify private key handle
MCHECK(mbedtls_md_hmac_update(&hmac_ctx, priv_key, sizeof(priv_key)));
MCHECK(mbedtls_md_hmac_update(&hmac_ctx, req->app_id, sizeof(req->app_id)));
MCHECK(mbedtls_md_hmac_finish(&hmac_ctx, mac_control));
}
if(memcmp(req->key_handle.hash, mac_control, sizeof(mac_control)) != 0) {
FURI_LOG_W(TAG, "Wrong handle!");
memcpy(&buf[0], state_wrong_data, 2);
return 2;
}
if(req->p1 == U2fCheckOnly) { // Check-only: don't need to send full response
memcpy(&buf[0], state_user_missing, 2);
return 2;
}
// Sign hash
u2f_ecc_sign(&U2F->group, priv_key, hash, signature);
resp->user_present = flags;
resp->counter = be_u2f_counter;
uint8_t signature_len = u2f_der_encode_signature(resp->signature, signature);
memcpy(resp->signature + signature_len, state_no_error, 2);
U2F->counter++;
FURI_LOG_D(TAG, "Counter: %lu", U2F->counter);
u2f_data_cnt_write(U2F->counter);
if(U2F->callback != NULL) U2F->callback(U2fNotifyAuthSuccess, U2F->context);
return (sizeof(U2fAuthResp) + signature_len + 2);
}
uint16_t u2f_msg_parse(U2fData* U2F, uint8_t* buf, uint16_t len) {
furi_assert(U2F);
if(!U2F->ready) return 0;
if((buf[0] != 0x00) && (len < 5)) return 0;
if(buf[1] == U2F_CMD_REGISTER) { // Register request
return u2f_register(U2F, buf);
} else if(buf[1] == U2F_CMD_AUTHENTICATE) { // Authenticate request
return u2f_authenticate(U2F, buf);
} else if(buf[1] == U2F_CMD_VERSION) { // Get U2F version string
memcpy(&buf[0], ver_str, 6);
memcpy(&buf[6], state_no_error, 2);
return 8;
} else {
memcpy(&buf[0], state_not_supported, 2);
return 2;
}
return 0;
}
void u2f_wink(U2fData* U2F) {
if(U2F->callback != NULL) U2F->callback(U2fNotifyWink, U2F->context);
}
void u2f_set_state(U2fData* U2F, uint8_t state) {
if(state == 0) {
if(U2F->callback != NULL) U2F->callback(U2fNotifyDisconnect, U2F->context);
} else {
if(U2F->callback != NULL) U2F->callback(U2fNotifyConnect, U2F->context);
}
U2F->user_present = false;
}
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