feat(core): Rework Optiga PIN slot configuration.

core/embed/trezorhal/optiga.h

@@ -69,8 +69,12 @@ int __wur optiga_pin_verify_v4(OPTIGA_UI_PROGRESS ui_progress,
                                const uint8_t pin_secret[OPTIGA_PIN_SECRET_SIZE],
                                uint8_t out_secret[OPTIGA_PIN_SECRET_SIZE]);
 
+int __wur optiga_pin_get_fails_v4(uint32_t *ctr);
+
 int __wur optiga_pin_get_fails(uint32_t *ctr);
 
+int __wur optiga_pin_fails_increase_v4(uint32_t count);
+
 int __wur optiga_pin_fails_increase(uint32_t count);
 
 #endif

core/embed/trezorhal/optiga/optiga.c

@@ -26,20 +26,29 @@
 #include "rand.h"
 #include "storage.h"
 
-// PIN counter reset key / Master secret (OID 0xF1D0).
+// Counter-protected PIN secret and reset key for OID_STRETCHED_PIN_CTR (OID
+// 0xF1D0).
 #define OID_PIN_SECRET (OPTIGA_OID_DATA + 0)
 
-// PIN counter (OID 0xE120).
+// Digest of the stretched PIN (OID 0xF1D4).
-#define OID_PIN_COUNTER (OPTIGA_OID_COUNTER + 0)
-
-// PIN stretching counter (OID 0xE121).
-#define OID_PIN_STRETCH_COUNTER (OPTIGA_OID_COUNTER + 1)
-
-// Stretched PIN (OID 0xF1D4).
 #define OID_STRETCHED_PIN (OPTIGA_OID_DATA + 4)
 
-// Key for HMAC-SHA256 PIN stretching step (OID 0xF1D1).
+// Counter-protected key for HMAC-SHA256 PIN stretching step (OID 0xF1D5).
-#define OID_PIN_HMAC (OPTIGA_OID_DATA + 1)
+#define OID_PIN_HMAC (OPTIGA_OID_DATA + 8)
+
+// Counter which limits the guesses at OID_STRETCHED_PIN (OID 0xE120).
+#define OID_STRETCHED_PIN_CTR (OPTIGA_OID_COUNTER + 0)
+
+// Counter which limits the use of OID_PIN_HMAC (OID 0xE122).
+#define OID_PIN_HMAC_CTR (OPTIGA_OID_COUNTER + 2)
+
+// Counter which limits the total number of PIN stretching operations over the
+// lifetime of the device (OID 0xE121).
+#define OID_PIN_TOTAL_CTR (OPTIGA_OID_COUNTER + 1)
+
+// Key for HMAC-SHA256 PIN stretching step used in storage version 3 and 4 (OID
+// 0xF1D1).
+#define OID_PIN_HMAC_V4 (OPTIGA_OID_DATA + 1)
 
 // Key for AES-CMAC PIN stretching step (OID 0xE200).
 #define OID_PIN_CMAC OPTIGA_OID_SYM_KEY
@@ -47,20 +56,17 @@
 // Key for ECDH PIN stretching step (OID 0xE0F3).
 #define OID_PIN_ECDH (OPTIGA_OID_ECC_KEY + 3)
 
-// The number of times the stretching is repeated in each PIN processing phase
-// for legacy storage version 3 and 4.
-#define PIN_STRETCH_ITERATIONS_V4 1
-
 // The number of times that PIN stretching is repeated.
 #define PIN_STRETCH_ITERATIONS 2
 
 // Value of the PIN counter when it is reset.
 static const uint8_t COUNTER_RESET[] = {0, 0, 0, 0, 0, 0, 0, PIN_MAX_TRIES};
 
-// Value of the PIN stretching counter when it is initialized. The limit is
+// Initial value of the counter which limits the total number of PIN stretching
-// 600000 stretching operations, which equates to
+// operations. The limit is 600000 stretching operations, which equates to
-// 100000 / PIN_STRETCH_ITERATIONS unlock operations.
+// 300000 / PIN_STRETCH_ITERATIONS unlock operations over the lifetime of the
-static const uint8_t STRETCH_COUNTER_INIT[] = {0, 0, 0, 0, 0, 0x09, 0x27, 0xC0};
+// device.
+static const uint8_t PIN_TOTAL_CTR_INIT[] = {0, 0, 0, 0, 0, 0x09, 0x27, 0xC0};
 
 static const optiga_metadata_item TYPE_AUTOREF =
     OPTIGA_META_VALUE(OPTIGA_DATA_TYPE_AUTOREF);
@@ -70,10 +76,12 @@ static const optiga_metadata_item ACCESS_STRETCHED_PIN =
     OPTIGA_ACCESS_CONDITION(OPTIGA_ACCESS_COND_AUTO, OID_STRETCHED_PIN);
 static const optiga_metadata_item ACCESS_PIN_SECRET =
     OPTIGA_ACCESS_CONDITION(OPTIGA_ACCESS_COND_AUTO, OID_PIN_SECRET);
-static const optiga_metadata_item ACCESS_PIN_COUNTER =
+static const optiga_metadata_item ACCESS_STRETCHED_PIN_CTR =
-    OPTIGA_ACCESS_CONDITION(OPTIGA_ACCESS_COND_LUC, OID_PIN_COUNTER);
+    OPTIGA_ACCESS_CONDITION(OPTIGA_ACCESS_COND_LUC, OID_STRETCHED_PIN_CTR);
-static const optiga_metadata_item ACCESS_PIN_STRETCH_COUNTER =
+static const optiga_metadata_item ACCESS_PIN_TOTAL_CTR =
-    OPTIGA_ACCESS_CONDITION(OPTIGA_ACCESS_COND_LUC, OID_PIN_STRETCH_COUNTER);
+    OPTIGA_ACCESS_CONDITION(OPTIGA_ACCESS_COND_LUC, OID_PIN_TOTAL_CTR);
+static const optiga_metadata_item ACCESS_PIN_HMAC_CTR =
+    OPTIGA_ACCESS_CONDITION(OPTIGA_ACCESS_COND_LUC, OID_PIN_HMAC_CTR);
 
 // Size of the DER BIT STRING header required for inputs to optiga_calc_ssec().
 #define BIT_STRING_HEADER_SIZE 3
@@ -244,7 +252,7 @@ bool optiga_set_metadata(uint16_t oid, const optiga_metadata *metadata) {
 static bool optiga_pin_init_metadata(void) {
   optiga_metadata metadata = {0};
 
-  // Set metadata for PIN counter reset key / Master secret.
+  // Set metadata for counter-protected PIN secret.
   memzero(&metadata, sizeof(metadata));
   metadata.change = OPTIGA_META_ACCESS_ALWAYS;
   metadata.read = ACCESS_STRETCHED_PIN;
@@ -254,43 +262,64 @@ static bool optiga_pin_init_metadata(void) {
     return false;
   }
 
-  // Set metadata for PIN counter.
+  // Set metadata for stretched PIN.
+  memzero(&metadata, sizeof(metadata));
+  metadata.change = ACCESS_PIN_SECRET;
+  metadata.read = OPTIGA_META_ACCESS_NEVER;
+  metadata.execute = ACCESS_STRETCHED_PIN_CTR;
+  metadata.data_type = TYPE_AUTOREF;
+  if (!optiga_set_metadata(OID_STRETCHED_PIN, &metadata)) {
+    return false;
+  }
+
+  // Set metadata for HMAC-SHA256 PIN stretching secret.
+  memzero(&metadata, sizeof(metadata));
+  metadata.change = ACCESS_STRETCHED_PIN;
+  metadata.read = OPTIGA_META_ACCESS_NEVER;
+  metadata.execute = ACCESS_PIN_HMAC_CTR;
+  metadata.data_type = TYPE_PRESSEC;
+  if (!optiga_set_metadata(OID_PIN_HMAC, &metadata)) {
+    return false;
+  }
+
+  // Set metadata for the counter of guesses at OID_STRETCHED_PIN.
   memzero(&metadata, sizeof(metadata));
   metadata.change = ACCESS_PIN_SECRET;
   metadata.read = OPTIGA_META_ACCESS_ALWAYS;
   metadata.execute = OPTIGA_META_ACCESS_ALWAYS;
-  if (!optiga_set_metadata(OID_PIN_COUNTER, &metadata)) {
+  if (!optiga_set_metadata(OID_STRETCHED_PIN_CTR, &metadata)) {
     return false;
   }
 
-  // Initialize the PIN stretching counter if write access is possible.
+  // Set metadata for the counter of OID_PIN_HMAC uses.
+  memzero(&metadata, sizeof(metadata));
+  metadata.change = ACCESS_STRETCHED_PIN;
+  metadata.read = OPTIGA_META_ACCESS_ALWAYS;
+  metadata.execute = OPTIGA_META_ACCESS_ALWAYS;
+  if (!optiga_set_metadata(OID_PIN_HMAC_CTR, &metadata)) {
+    return false;
+  }
+
+  // Initialize the counter of the total number of PIN stretching operations, if
+  // write access is possible.
   memzero(&metadata, sizeof(metadata));
   metadata.change = OPTIGA_META_ACCESS_ALWAYS;
-  if (write_metadata(OID_PIN_STRETCH_COUNTER, &metadata)) {
+  if (write_metadata(OID_PIN_TOTAL_CTR, &metadata)) {
-    optiga_result res = optiga_set_data_object(OID_PIN_STRETCH_COUNTER, false,
+    optiga_result res =
-                                               STRETCH_COUNTER_INIT,
+        optiga_set_data_object(OID_PIN_TOTAL_CTR, false, PIN_TOTAL_CTR_INIT,
-                                               sizeof(STRETCH_COUNTER_INIT));
+                               sizeof(PIN_TOTAL_CTR_INIT));
     if (res != OPTIGA_SUCCESS) {
       return false;
     }
   }
 
-  // Set metadata for PIN stretching counter.
+  // Set metadata for the counter of the total number of PIN stretching
+  // operations.
   memzero(&metadata, sizeof(metadata));
   metadata.change = OPTIGA_META_ACCESS_NEVER;
   metadata.read = OPTIGA_META_ACCESS_ALWAYS;
   metadata.execute = OPTIGA_META_ACCESS_ALWAYS;
-  if (!optiga_set_metadata(OID_PIN_STRETCH_COUNTER, &metadata)) {
+  if (!optiga_set_metadata(OID_PIN_TOTAL_CTR, &metadata)) {
-    return false;
-  }
-
-  // Set metadata for stretched PIN.
-  memzero(&metadata, sizeof(metadata));
-  metadata.change = ACCESS_PIN_SECRET;
-  metadata.read = OPTIGA_META_ACCESS_NEVER;
-  metadata.execute = ACCESS_PIN_COUNTER;
-  metadata.data_type = TYPE_AUTOREF;
-  if (!optiga_set_metadata(OID_STRETCHED_PIN, &metadata)) {
     return false;
   }
 
@@ -298,7 +327,7 @@ static bool optiga_pin_init_metadata(void) {
   memzero(&metadata, sizeof(metadata));
   metadata.change = OPTIGA_META_ACCESS_ALWAYS;
   metadata.read = OPTIGA_META_ACCESS_NEVER;
-  metadata.execute = ACCESS_PIN_STRETCH_COUNTER;
+  metadata.execute = ACCESS_PIN_TOTAL_CTR;
   metadata.key_usage = OPTIGA_META_KEY_USE_ENC;
   if (!optiga_set_metadata(OID_PIN_CMAC, &metadata)) {
     return false;
@@ -308,41 +337,12 @@ static bool optiga_pin_init_metadata(void) {
   memzero(&metadata, sizeof(metadata));
   metadata.change = OPTIGA_META_ACCESS_ALWAYS;
   metadata.read = OPTIGA_META_ACCESS_NEVER;
-  metadata.execute = ACCESS_PIN_STRETCH_COUNTER;
+  metadata.execute = ACCESS_PIN_TOTAL_CTR;
   metadata.key_usage = OPTIGA_META_KEY_USE_KEYAGREE;
   if (!optiga_set_metadata(OID_PIN_ECDH, &metadata)) {
     return false;
   }
 
-  // Generate and store the HMAC PIN stretching secret in OID_PIN_HMAC, if write
-  // access is possible.
-  memzero(&metadata, sizeof(metadata));
-  metadata.change = OPTIGA_META_ACCESS_ALWAYS;
-  if (write_metadata(OID_PIN_HMAC, &metadata)) {
-    uint8_t secret[OPTIGA_PIN_SECRET_SIZE] = {0};
-    optiga_result res = optiga_get_random(secret, sizeof(secret));
-    if (res != OPTIGA_SUCCESS) {
-      return false;
-    }
-    random_xor(secret, sizeof(secret));
-
-    res = optiga_set_data_object(OID_PIN_HMAC, false, secret, sizeof(secret));
-    memzero(secret, sizeof(secret));
-    if (res != OPTIGA_SUCCESS) {
-      return false;
-    }
-  }
-
-  // Set metadata for HMAC-SHA256 PIN stretching secret.
-  memzero(&metadata, sizeof(metadata));
-  metadata.change = OPTIGA_META_ACCESS_NEVER;
-  metadata.read = OPTIGA_META_ACCESS_NEVER;
-  metadata.execute = ACCESS_PIN_STRETCH_COUNTER;
-  metadata.data_type = TYPE_PRESSEC;
-  if (!optiga_set_metadata(OID_PIN_HMAC, &metadata)) {
-    return false;
-  }
-
   return true;
 }
 
@@ -369,9 +369,10 @@ static int optiga_pin_init_stretch(void) {
 
 static int optiga_pin_stretch_common(
     OPTIGA_UI_PROGRESS ui_progress, HMAC_SHA256_CTX *ctx,
-    const uint8_t input[OPTIGA_PIN_SECRET_SIZE]) {
+    const uint8_t input[OPTIGA_PIN_SECRET_SIZE], bool version4) {
-  // Implements the functionality that is common to optiga_pin_stretch_secret()
+  // Implements the functionality that is common to
-  // and the legacy function optiga_pin_stretch_secret_v4().
+  // optiga_pin_stretch_cmac_ecdh() and the legacy function
+  // optiga_pin_stretch_secret_v4().
 
   uint8_t buffer[ENCRYPT_SYM_PREFIX_SIZE + OPTIGA_PIN_SECRET_SIZE] = {0};
   size_t size = 0;
@@ -387,16 +388,18 @@ static int optiga_pin_stretch_common(
 
   hmac_sha256_Update(ctx, buffer, size);
 
+  if (version4) {
     // Combine intermediate result with OID_PIN_HMAC
-  res =
+    res = optiga_encrypt_sym(OPTIGA_SYM_MODE_HMAC_SHA256, OID_PIN_HMAC_V4,
-      optiga_encrypt_sym(OPTIGA_SYM_MODE_HMAC_SHA256, OID_PIN_HMAC, input,
+                             input, OPTIGA_PIN_SECRET_SIZE, buffer,
-                         OPTIGA_PIN_SECRET_SIZE, buffer, sizeof(buffer), &size);
+                             sizeof(buffer), &size);
     if (res != OPTIGA_SUCCESS) {
       memzero(buffer, sizeof(buffer));
       return res;
     }
 
     hmac_sha256_Update(ctx, buffer, size);
+  }
 
   ui_progress(200);
 
@@ -435,39 +438,27 @@ static int optiga_pin_stretch_secret_v4(
   // in each attempt.
 
   // Pseudocode for the stretching process:
-  // result_0 = secret
+  // cmac_out = CMAC(OID_PIN_CMAC, secret)
-  // for i in range(PIN_STRETCH_ITERATIONS_V4):
+  // hmac_out = HMAC(OID_PIN_HMAC_V4, secret)
-  //   cmac_i = CMAC(optiga_cmac_key, result_i)
+  // ecdh_out = ECDH(OID_PIN_ECDH, secret)
-  //   hmac_i = HMAC(optiga_hmac_key, result_i)
+  // secret = HMAC-SHA256(secret, cmac_out || hmac_out || ecdh_out)
-  //   ecdh_i = ECDH(optiga_ecdh_key, result_i)
-  //   result_{i+1} = HMAC-SHA256(secret, cmac_i || hmac_i || ecdh_i)
-  // secret = result_{PIN_STRETCH_ITERATIONS_V4}
 
   HMAC_SHA256_CTX ctx = {0};
-
-  uint8_t result[OPTIGA_PIN_SECRET_SIZE] = {0};
-  memcpy(result, secret, sizeof(result));
-
-  for (int i = 0; i < PIN_STRETCH_ITERATIONS_V4; ++i) {
   hmac_sha256_Init(&ctx, secret, OPTIGA_PIN_SECRET_SIZE);
 
-    optiga_result res = optiga_pin_stretch_common(ui_progress, &ctx, result);
+  optiga_result res =
+      optiga_pin_stretch_common(ui_progress, &ctx, secret, true);
   if (res != OPTIGA_SUCCESS) {
-      memzero(result, sizeof(result));
     memzero(&ctx, sizeof(ctx));
     return res;
   }
 
-    hmac_sha256_Final(&ctx, result);
+  hmac_sha256_Final(&ctx, secret);
-  }
-
-  memcpy(secret, result, sizeof(result));
-  memzero(result, sizeof(result));
   memzero(&ctx, sizeof(ctx));
   return OPTIGA_SUCCESS;
 }
 
-static int optiga_pin_stretch_secret(
+static int optiga_pin_stretch_cmac_ecdh(
     OPTIGA_UI_PROGRESS ui_progress,
     uint8_t stretched_pin[OPTIGA_PIN_SECRET_SIZE]) {
   // This step hardens the PIN verification process in case an attacker is able
@@ -478,15 +469,14 @@ static int optiga_pin_stretch_secret(
   // search for the PIN. Thus it reduces the number of PIN values that the
   // attacker can test in a unit of time by forcing them to involve the Optiga
   // in each attempt, and restricts the overall number of attempts using
-  // OID_PIN_STRETCH_COUNTER.
+  // OID_PIN_TOTAL_CTR.
 
   // Pseudocode for the stretching process:
-  // for i in range(PIN_STRETCH_ITERATIONS):
+  // for _ in range(PIN_STRETCH_ITERATIONS):
-  //   digest = HMAC(secret, "")
+  //   digest = HMAC-SHA256(stretched_pin, "")
-  //   cmac_i = CMAC(optiga_cmac_key, digest)
+  //   cmac_out = CMAC(OID_PIN_CMAC, digest)
-  //   hmac_i = HMAC(optiga_hmac_key, digest)
+  //   ecdh_out = ECDH(OID_PIN_ECDH, digest)
-  //   ecdh_i = ECDH(optiga_ecdh_key, digest)
+  //   stretched_pin = HMAC-SHA256(stretched_pin, cmac_out || ecdh_out)
-  //   secret = HMAC-SHA256(secret, cmac_i || hmac_i || ecdh_i)
 
   uint8_t digest[OPTIGA_PIN_SECRET_SIZE] = {0};
   HMAC_SHA256_CTX ctx = {0};
@@ -498,7 +488,8 @@ static int optiga_pin_stretch_secret(
     hmac_sha256(stretched_pin, OPTIGA_PIN_SECRET_SIZE, NULL, 0, digest);
     hmac_sha256_Init(&ctx, stretched_pin, OPTIGA_PIN_SECRET_SIZE);
 
-    optiga_result res = optiga_pin_stretch_common(ui_progress, &ctx, digest);
+    optiga_result res =
+        optiga_pin_stretch_common(ui_progress, &ctx, digest, false);
     if (res != OPTIGA_SUCCESS) {
       memzero(digest, sizeof(digest));
       memzero(&ctx, sizeof(ctx));
@@ -515,13 +506,15 @@ static int optiga_pin_stretch_secret(
 
 int optiga_pin_set(OPTIGA_UI_PROGRESS ui_progress,
                    uint8_t stretched_pin[OPTIGA_PIN_SECRET_SIZE]) {
+  int res = OPTIGA_SUCCESS;
   if (!optiga_pin_init_metadata()) {
-    return -1;
+    res = -1;
+    goto end;
   }
 
-  optiga_result res = optiga_pin_init_stretch();
+  res = optiga_pin_init_stretch();
   if (res != OPTIGA_SUCCESS) {
-    return res;
+    goto end;
   }
 
   ui_progress(200);
@@ -530,43 +523,110 @@ int optiga_pin_set(OPTIGA_UI_PROGRESS ui_progress,
   // ensures that if an attacker extracts the value of OID_STRETCHED_PIN or
   // OID_PIN_SECRET, then it cannot be used to conduct an offline brute-force
   // search for the PIN.
-  res = optiga_pin_stretch_secret(ui_progress, stretched_pin);
+  res = optiga_pin_stretch_cmac_ecdh(ui_progress, stretched_pin);
   if (res != OPTIGA_SUCCESS) {
-    return res;
+    goto end;
   }
 
   // Generate and store the counter-protected PIN secret.
   uint8_t pin_secret[OPTIGA_PIN_SECRET_SIZE] = {0};
   res = optiga_get_random(pin_secret, sizeof(pin_secret));
   if (res != OPTIGA_SUCCESS) {
-    return res;
+    goto end;
   }
   random_xor(pin_secret, sizeof(pin_secret));
 
   res = optiga_set_data_object(OID_PIN_SECRET, false, pin_secret,
                                sizeof(pin_secret));
   if (res != OPTIGA_SUCCESS) {
-    return res;
+    goto end;
   }
 
-  // Authorise using OID_PIN_SECRET so that we can write to OID_PIN_COUNTER and
+  // Generate the key for the HMAC-SHA256 PIN stretching step.
-  // OID_STRETCHED_PIN.
+  uint8_t pin_hmac[OPTIGA_PIN_SECRET_SIZE] = {0};
+  res = optiga_get_random(pin_hmac, sizeof(pin_hmac));
+  if (res != OPTIGA_SUCCESS) {
+    goto end;
+  }
+  random_xor(pin_hmac, sizeof(pin_hmac));
+
+  // Authorise using OID_PIN_SECRET so that we can write to OID_STRETCHED_PIN
+  // and OID_STRETCHED_PIN_CTR.
   res = optiga_set_auto_state(OPTIGA_OID_SESSION_CTX, OID_PIN_SECRET,
                               pin_secret, sizeof(pin_secret));
   if (res != OPTIGA_SUCCESS) {
-    return res;
+    goto end;
   }
 
+  // Process the stretched PIN using a one-way function before using it in the
+  // operation that will be executed in Optiga during verification. This ensures
+  // that in the unlikely case of an attacker recording communication between
+  // the MCU and Optiga, they will not gain knowledge of the stretched PIN.
+  uint8_t digest[OPTIGA_PIN_SECRET_SIZE] = {0};
+  hmac_sha256(stretched_pin, OPTIGA_PIN_SECRET_SIZE, NULL, 0, digest);
+
+  // Compute the operation that will be executed in Optiga during verification.
+  uint8_t hmac_buffer[ENCRYPT_SYM_PREFIX_SIZE + OPTIGA_PIN_SECRET_SIZE] = {
+      0x61, 0x00, 0x20};
+  hmac_sha256(pin_hmac, sizeof(pin_hmac), digest, sizeof(digest),
+              &hmac_buffer[ENCRYPT_SYM_PREFIX_SIZE]);
+
+  // Stretch the PIN with the result.
+  hmac_sha256(stretched_pin, OPTIGA_PIN_SECRET_SIZE, hmac_buffer,
+              sizeof(hmac_buffer), stretched_pin);
+
   // Process the stretched PIN using a one-way function before sending it to the
   // Optiga. This ensures that in the unlikely case of an attacker recording
   // communication between the MCU and Optiga, they will not gain knowledge of
   // the stretched PIN.
-  uint8_t digest[OPTIGA_PIN_SECRET_SIZE] = {0};
   hmac_sha256(stretched_pin, OPTIGA_PIN_SECRET_SIZE, NULL, 0, digest);
 
   // Store the digest of the stretched PIN in OID_STRETCHED_PIN.
   res =
       optiga_set_data_object(OID_STRETCHED_PIN, false, digest, sizeof(digest));
+  if (res != OPTIGA_SUCCESS) {
+    goto end;
+  }
+
+  // Initialize the counter which limits the guesses at OID_STRETCHED_PIN so
+  // that we can authorise using OID_STRETCHED_PIN.
+  res = optiga_set_data_object(OID_STRETCHED_PIN_CTR, false, COUNTER_RESET,
+                               sizeof(COUNTER_RESET));
+  if (res != OPTIGA_SUCCESS) {
+    goto end;
+  }
+
+  // Authorise using OID_STRETCHED_PIN so that we can write to OID_PIN_HMAC and
+  // OID_PIN_HMAC_CTR.
+  res = optiga_set_auto_state(OPTIGA_OID_SESSION_CTX, OID_STRETCHED_PIN, digest,
+                              sizeof(digest));
+  if (res != OPTIGA_SUCCESS) {
+    goto end;
+  }
+
+  // Initialize the key for HMAC-SHA256 PIN stretching.
+  res = optiga_set_data_object(OID_PIN_HMAC, false, pin_hmac, sizeof(pin_hmac));
+  if (res != OPTIGA_SUCCESS) {
+    goto end;
+  }
+
+  // Initialize the counter which limits the guesses at OID_STRETCHED_PIN again,
+  // since we just depleted one attempt.
+  res = optiga_set_data_object(OID_STRETCHED_PIN_CTR, false, COUNTER_RESET,
+                               sizeof(COUNTER_RESET));
+  optiga_clear_auto_state(OID_PIN_SECRET);
+  if (res != OPTIGA_SUCCESS) {
+    goto end;
+  }
+
+  // Initialize the PIN counter which limits the use of OID_PIN_HMAC.
+  res = optiga_set_data_object(OID_PIN_HMAC_CTR, false, COUNTER_RESET,
+                               sizeof(COUNTER_RESET));
+  if (res != OPTIGA_SUCCESS) {
+    goto end;
+  }
+
+  ui_progress(200);
 
   // Stretch the PIN more with the counter-protected PIN secret. This method
   // ensures that if the user chooses a high-entropy PIN, then even if the
@@ -575,24 +635,18 @@ int optiga_pin_set(OPTIGA_UI_PROGRESS ui_progress,
   // integrated into the device in the first place.
   hmac_sha256(stretched_pin, OPTIGA_PIN_SECRET_SIZE, pin_secret,
               sizeof(pin_secret), stretched_pin);
+  if (res != OPTIGA_SUCCESS) {
+    goto end;
+  }
+
+end:
+  memzero(hmac_buffer, sizeof(hmac_buffer));
+  memzero(pin_hmac, sizeof(pin_hmac));
   memzero(pin_secret, sizeof(pin_secret));
   memzero(digest, sizeof(digest));
-  if (res != OPTIGA_SUCCESS) {
   optiga_clear_auto_state(OID_PIN_SECRET);
+  optiga_clear_auto_state(OID_STRETCHED_PIN);
   return res;
-  }
-
-  // Initialize the PIN counter.
-  res = optiga_set_data_object(OID_PIN_COUNTER, false, COUNTER_RESET,
-                               sizeof(COUNTER_RESET));
-  optiga_clear_auto_state(OID_PIN_SECRET);
-  if (res != OPTIGA_SUCCESS) {
-    return res;
-  }
-
-  ui_progress(200);
-
-  return OPTIGA_SUCCESS;
 }
 
 int optiga_pin_verify_v4(OPTIGA_UI_PROGRESS ui_progress,
@@ -648,14 +702,6 @@ int optiga_pin_verify_v4(OPTIGA_UI_PROGRESS ui_progress,
     return res;
   }
 
-  // Reset the PIN counter.
-  res = optiga_set_data_object(OID_PIN_COUNTER, false, COUNTER_RESET,
-                               sizeof(COUNTER_RESET));
-  optiga_clear_auto_state(OID_PIN_SECRET);
-  if (res != OPTIGA_SUCCESS) {
-    return res;
-  }
-
   ui_progress(200);
 
   // Combine the value of OID_PIN_SECRET with the PIN-derived secret and
@@ -674,10 +720,47 @@ int optiga_pin_verify_v4(OPTIGA_UI_PROGRESS ui_progress,
   return OPTIGA_SUCCESS;
 }
 
+static int optiga_pin_stretch_hmac(
+    uint8_t stretched_pin[OPTIGA_PIN_SECRET_SIZE]) {
+  // Process the stretched PIN using a one-way function before sending it to the
+  // Optiga.
+  uint8_t digest[OPTIGA_PIN_SECRET_SIZE] = {0};
+  hmac_sha256(stretched_pin, OPTIGA_PIN_SECRET_SIZE, NULL, 0, digest);
+
+  // HMAC the digest with the key in OID_PIN_HMAC.
+  uint8_t hmac_buffer[ENCRYPT_SYM_PREFIX_SIZE + OPTIGA_PIN_SECRET_SIZE] = {0};
+  size_t size = 0;
+  optiga_result res = optiga_encrypt_sym(
+      OPTIGA_SYM_MODE_HMAC_SHA256, OID_PIN_HMAC, digest, sizeof(digest),
+      hmac_buffer, sizeof(hmac_buffer), &size);
+  memzero(digest, sizeof(digest));
+  if (res != OPTIGA_SUCCESS) {
+    uint8_t error_code = 0;
+    optiga_get_error_code(&error_code);
+    if (error_code + OPTIGA_COMMAND_ERROR_OFFSET ==
+        OPTIGA_ERR_ACCESS_COND_NOT_SAT) {
+      return OPTIGA_ERR_COUNTER_EXCEEDED;
+    } else {
+      return error_code + OPTIGA_COMMAND_ERROR_OFFSET;
+    }
+  }
+
+  // Stretch the PIN with the result.
+  hmac_sha256(stretched_pin, OPTIGA_PIN_SECRET_SIZE, hmac_buffer, size,
+              stretched_pin);
+  memzero(hmac_buffer, sizeof(hmac_buffer));
+  return OPTIGA_SUCCESS;
+}
+
 int optiga_pin_verify(OPTIGA_UI_PROGRESS ui_progress,
                       uint8_t stretched_pin[OPTIGA_PIN_SECRET_SIZE]) {
   // Stretch the PIN more with stretching secrets from the Optiga.
-  optiga_result res = optiga_pin_stretch_secret(ui_progress, stretched_pin);
+  optiga_result res = optiga_pin_stretch_cmac_ecdh(ui_progress, stretched_pin);
+  if (res != OPTIGA_SUCCESS) {
+    return res;
+  }
+
+  res = optiga_pin_stretch_hmac(stretched_pin);
   if (res != OPTIGA_SUCCESS) {
     return res;
   }
@@ -687,7 +770,8 @@ int optiga_pin_verify(OPTIGA_UI_PROGRESS ui_progress,
   uint8_t digest[OPTIGA_PIN_SECRET_SIZE] = {0};
   hmac_sha256(stretched_pin, OPTIGA_PIN_SECRET_SIZE, NULL, 0, digest);
 
-  // Authorise using OID_STRETCHED_PIN so that we can read from OID_PIN_SECRET.
+  // Authorise using OID_STRETCHED_PIN so that we can read from OID_PIN_SECRET
+  // and reset OID_PIN_HMAC_CTR.
   res = optiga_set_auto_state(OPTIGA_OID_SESSION_CTX, OID_STRETCHED_PIN, digest,
                               sizeof(digest));
   memzero(digest, sizeof(digest));
@@ -697,10 +781,16 @@ int optiga_pin_verify(OPTIGA_UI_PROGRESS ui_progress,
     return error_code + OPTIGA_COMMAND_ERROR_OFFSET;
   }
 
+  // Reset the counter which limits the use of OID_PIN_HMAC.
+  res = optiga_set_data_object(OID_PIN_HMAC_CTR, false, COUNTER_RESET,
+                               sizeof(COUNTER_RESET));
   if (res != OPTIGA_SUCCESS) {
+    optiga_clear_auto_state(OID_STRETCHED_PIN);
     return res;
   }
 
+  ui_progress(200);
+
   // Read the counter-protected PIN secret from OID_PIN_SECRET.
   uint8_t pin_secret[OPTIGA_PIN_SECRET_SIZE] = {0};
   size_t size = 0;
@@ -711,26 +801,20 @@ int optiga_pin_verify(OPTIGA_UI_PROGRESS ui_progress,
     return res;
   }
 
-  if (size != OPTIGA_PIN_SECRET_SIZE) {
-    return OPTIGA_ERR_SIZE;
-  }
-
   // Stretch the PIN more with the counter-protected PIN secret.
-  hmac_sha256(stretched_pin, OPTIGA_PIN_SECRET_SIZE, pin_secret,
+  hmac_sha256(stretched_pin, OPTIGA_PIN_SECRET_SIZE, pin_secret, size,
-              OPTIGA_PIN_SECRET_SIZE, stretched_pin);
+              stretched_pin);
 
-  ui_progress(200);
+  // Authorise using OID_PIN_SECRET so that we can reset OID_STRETCHED_PIN_CTR.
-
-  // Authorise using OID_PIN_SECRET so that we can write to OID_PIN_COUNTER.
   res = optiga_set_auto_state(OPTIGA_OID_SESSION_CTX, OID_PIN_SECRET,
-                              pin_secret, OPTIGA_PIN_SECRET_SIZE);
+                              pin_secret, sizeof(pin_secret));
   memzero(pin_secret, sizeof(pin_secret));
   if (res != OPTIGA_SUCCESS) {
     return res;
   }
 
-  // Reset the PIN counter.
+  // Reset the counter which limits the guesses at OID_STRETCHED_PIN.
-  res = optiga_set_data_object(OID_PIN_COUNTER, false, COUNTER_RESET,
+  res = optiga_set_data_object(OID_STRETCHED_PIN_CTR, false, COUNTER_RESET,
                                sizeof(COUNTER_RESET));
   optiga_clear_auto_state(OID_PIN_SECRET);
   if (res != OPTIGA_SUCCESS) {
@@ -763,8 +847,43 @@ static int optiga_get_counter(uint16_t oid, uint32_t *ctr) {
   return OPTIGA_SUCCESS;
 }
 
+int optiga_pin_get_fails_v4(uint32_t *ctr) {
+  return optiga_get_counter(OID_STRETCHED_PIN_CTR, ctr);
+}
+
 int optiga_pin_get_fails(uint32_t *ctr) {
-  return optiga_get_counter(OID_PIN_COUNTER, ctr);
+  uint32_t ctr1 = 0;
+  uint32_t ctr2 = 0;
+  if (optiga_get_counter(OID_PIN_HMAC_CTR, &ctr1) != OPTIGA_SUCCESS ||
+      optiga_get_counter(OID_STRETCHED_PIN_CTR, &ctr2) != OPTIGA_SUCCESS) {
+    return -1;
+  }
+
+  // Ensure that the counters are in sync.
+  if (ctr1 > ctr2) {
+    if (optiga_count_data_object(OID_STRETCHED_PIN_CTR, ctr1 - ctr2) !=
+        OPTIGA_SUCCESS) {
+      return -1;
+    }
+    *ctr = ctr1;
+  } else if (ctr2 > ctr1) {
+    if (optiga_count_data_object(OID_PIN_HMAC_CTR, ctr2 - ctr1) !=
+        OPTIGA_SUCCESS) {
+      return -1;
+    }
+    *ctr = ctr2;
+  } else {
+    *ctr = ctr2;
+  }
+  return OPTIGA_SUCCESS;
+}
+
+int optiga_pin_fails_increase_v4(uint32_t count) {
+  if (count > 0xff) {
+    return OPTIGA_ERR_PARAM;
+  }
+
+  return optiga_count_data_object(OID_STRETCHED_PIN_CTR, count);
 }
 
 int optiga_pin_fails_increase(uint32_t count) {
@@ -772,5 +891,10 @@ int optiga_pin_fails_increase(uint32_t count) {
     return OPTIGA_ERR_PARAM;
   }
 
-  return optiga_count_data_object(OID_PIN_COUNTER, count);
+  if (optiga_count_data_object(OID_PIN_HMAC_CTR, count) != OPTIGA_SUCCESS ||
+      optiga_count_data_object(OID_STRETCHED_PIN_CTR, count) !=
+          OPTIGA_SUCCESS) {
+    return -1;
+  }
+  return OPTIGA_SUCCESS;
 }

core/embed/trezorhal/unix/optiga.c

@@ -174,9 +174,16 @@ int optiga_pin_verify(OPTIGA_UI_PROGRESS ui_progress,
   return OPTIGA_SUCCESS;
 }
 
+int optiga_pin_get_fails_v4(uint32_t *ctr) {
+  *ctr = 0;
+  return OPTIGA_SUCCESS;
+}
+
 int optiga_pin_get_fails(uint32_t *ctr) {
   *ctr = 0;
   return OPTIGA_SUCCESS;
 }
 
+int optiga_pin_fails_increase_v4(uint32_t count) { return OPTIGA_SUCCESS; }
+
 int optiga_pin_fails_increase(uint32_t count) { return OPTIGA_SUCCESS; }

storage/storage.c

@@ -1275,8 +1275,13 @@ uint32_t storage_get_pin_rem(void) {
 #if USE_OPTIGA
   // Synchronize counters in case they diverged.
   uint32_t ctr_optiga = 0;
-  ensure(
+  optiga_result ret = OPTIGA_SUCCESS;
-      optiga_pin_get_fails(&ctr_optiga) == OPTIGA_SUCCESS ? sectrue : secfalse,
+  if (get_lock_version() >= 5) {
+    ret = optiga_pin_get_fails(&ctr_optiga);
+  } else {
+    ret = optiga_pin_get_fails_v4(&ctr_optiga);
+  }
+  ensure(ret == OPTIGA_SUCCESS ? sectrue : secfalse,
          "optiga_pin_get_fails failed");
 
   while (ctr_mcu < ctr_optiga) {
@@ -1285,9 +1290,12 @@ uint32_t storage_get_pin_rem(void) {
   }
 
   if (ctr_optiga < ctr_mcu) {
-    ensure(optiga_pin_fails_increase(ctr_mcu - ctr_optiga) == OPTIGA_SUCCESS
+    if (get_lock_version() >= 5) {
-               ? sectrue
+      ret = optiga_pin_fails_increase(ctr_mcu - ctr_optiga);
-               : secfalse,
+    } else {
+      ret = optiga_pin_fails_increase_v4(ctr_mcu - ctr_optiga);
+    }
+    ensure(ret == OPTIGA_SUCCESS ? sectrue : secfalse,
            "optiga_pin_fails_increase failed");
   }
 #endif