feat(core): allow unprovisioned tropic run in non-production fw
What the developer wrote
Authored by cepetr
feat(core): allow unprovisioned tropic run in non-production fw
[no changelog]
What changed, and why it matters
This commit adds a development-only code path for Trezor hardware wallets that use the Tropic secure chip. In non-production firmware builds, if the device lacks the normal Trezor private key, it falls back to a publicly visible factory private key and a factory pairing key slot. This lets developers test devices that have not yet been provisioned with unique secrets. The change is wrapped in `#if !PRODUCTION` guards, so it should not compile into retail firmware, but it does embed a hardcoded private key in the source tree.
Verify that `PRODUCTION` is always defined for official release builds and that CI blocks accidental shipping of non-production firmware. Treat the hardcoded factory key as a development/test credential, rotate it if it has ever been used in field devices, and ensure it is not present in released binaries. Review whether the delay value and certificate-store fallback have any side effects on boot time or secure-element state.
Security signals we found
Hardcoded cryptographic private key in source code
Factory-default key fallback for unprovisioned devices
Conditional compilation (`#if !PRODUCTION`) intended to exclude the fallback from production builds
Addition of `hal_delay(100)` to work around Tropic01 `LT_L1_CHIP_BUSY` responses
New certificate-store parsing helper to retrieve Tropic public key when normal provisioning data is absent
Evidence from the diff
The patch modifies core/embed/sec/tropic/tropic.c. It declares a helper tropic_get_tropic_pubkey() only for non-production builds, adds a 100 ms hal_delay() before pairing-key selection, and introduces a fallback under #if !PRODUCTION: if secret_key_tropic() does not yield a valid Trezor private key, the code copies a static 32-byte factory_private Curve25519 scalar into trezor_privkey, switches to TROPIC_FACTORY_PAIRING_KEY_SLOT, and marks the private key as valid. If the Tropic public key is also unavailable, the new helper reads it from the chip’s certificate store. The session is then started with these possibly factory-default credentials. The hardcoded scalar is visible in the diff.
Changed components
core/embed/sec/tropic/tropic.cTropic01 secure-element integrationTrezor Core firmware non-production buildsDevice provisioning / key injection flowInspect captured patch +55 / −3
diff --git a/core/embed/sec/tropic/tropic.c b/core/embed/sec/tropic/tropic.c
index 4ca1d6540..3d22fa26a 100644
--- a/core/embed/sec/tropic/tropic.c
+++ b/core/embed/sec/tropic/tropic.c
@@ -48,6 +48,11 @@ typedef struct {
static tropic_driver_t g_tropic_driver = {0};
+#if !PRODUCTION
+static bool tropic_get_tropic_pubkey(lt_handle_t *handle,
+ curve25519_key pubkey);
+#endif
+
bool tropic_init(void) {
tropic_driver_t *drv = &g_tropic_driver;
@@ -65,6 +70,10 @@ bool tropic_init(void) {
goto cleanup;
}
+ // Note: Without the delay below Tropic01 may return LT_L1_CHIP_BUSY. The
+ // length was chosen arbitrarily. A shorter delay may be sufficient.
+ hal_delay(100);
+
#ifdef TREZOR_EMULATOR
pkey_index_t pairing_key_slot = TROPIC_FACTORY_PAIRING_KEY_SLOT;
#else
@@ -80,13 +89,29 @@ bool tropic_init(void) {
curve25519_key tropic_pubkey = {0};
secbool pubkey_ok = secret_key_tropic_public(tropic_pubkey);
+
+#if !PRODUCTION
+ // Allow running with default factory keys in non-production fw
+ if (privkey_ok != sectrue) {
+ static const curve25519_key factory_private = {
+ 0x28, 0x3f, 0x5a, 0x0f, 0xfc, 0x41, 0xcf, 0x50, 0x98, 0xa8, 0xe1,
+ 0x7d, 0xb6, 0x37, 0x2c, 0x3c, 0xaa, 0xd1, 0xee, 0xee, 0xdf, 0x0f,
+ 0x75, 0xbc, 0x3f, 0xbf, 0xcd, 0x9c, 0xab, 0x3d, 0xe9, 0x72};
+
+ pairing_key_slot = TROPIC_FACTORY_PAIRING_KEY_SLOT;
+ memcpy(trezor_privkey, factory_private, sizeof(trezor_privkey));
+ privkey_ok = sectrue;
+ }
+
+ if (pubkey_ok != sectrue) {
+ pubkey_ok = tropic_get_tropic_pubkey(&drv->handle, tropic_pubkey) * sectrue;
+ }
+#endif
+
if (pubkey_ok == sectrue && privkey_ok == sectrue) {
curve25519_key trezor_pubkey = {0};
curve25519_scalarmult_basepoint(trezor_pubkey, trezor_privkey);
- // Note: Without the delay below Tropic01 may return LT_L1_CHIP_BUSY. The
- // length was chosen arbitrarily. A shorter delay may be sufficient.
- hal_delay(100);
lt_ret_t ret =
lt_session_start(&drv->handle, tropic_pubkey, pairing_key_slot,
trezor_privkey, trezor_pubkey);
@@ -184,6 +209,33 @@ bool tropic_data_read(uint16_t udata_slot, uint8_t *data, uint16_t *size) {
return res == LT_OK;
}
+#if !PRODUCTION
+static bool tropic_get_tropic_pubkey(lt_handle_t *handle,
+ curve25519_key pubkey) {
+ uint8_t buffer[LT_NUM_CERTIFICATES * LT_L2_GET_INFO_REQ_CERT_SIZE_SINGLE];
+
+ struct lt_cert_store_t cert_store = {0};
+ for (size_t i = 0; i < LT_NUM_CERTIFICATES; i++) {
+ cert_store.certs[i] = &buffer[i * LT_L2_GET_INFO_REQ_CERT_SIZE_SINGLE];
+ cert_store.buf_len[i] = LT_L2_GET_INFO_REQ_CERT_SIZE_SINGLE;
+ }
+
+ lt_ret_t ret = LT_FAIL;
+
+ ret = lt_get_info_cert_store(handle, &cert_store);
+ if (ret != LT_OK) {
+ return false;
+ }
+
+ ret = lt_get_st_pub(&cert_store, pubkey, sizeof(curve25519_key));
+ if (ret != LT_OK) {
+ return false;
+ }
+
+ return true;
+}
+#endif // !PRODUCTION
+
#endif // SECURE_MODE
bool tropic_data_multi_size(uint16_t first_slot, size_t *data_length) {
Why this scored 31/100
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