From b686df86841602c55c25134526b0862ea33d6f93 Mon Sep 17 00:00:00 2001
From: Pol Henarejos <pol.henarejos@cttc.es>
Date: Fri, 14 Aug 2026 23:34:32 +0200
Subject: [PATCH] Require fixed-size reference change bodies

Signed-off-by: Pol Henarejos <pol.henarejos@cttc.es>
---
 src/openpgp/piv.c                 | 32 +++++++++++++++++++++++--------
 tests/piv/test_060_regressions.py |  5 +++++
 2 files changed, 29 insertions(+), 8 deletions(-)

diff --git a/src/openpgp/piv.c b/src/openpgp/piv.c
index 8aadc4c..a4d615e 100644
--- a/src/openpgp/piv.c
+++ b/src/openpgp/piv.c
@@ -56,6 +56,7 @@
 #define PINPOLICY_ONCE 2
 #define PINPOLICY_ALWAYS 3
 #define MGM_PIN_POLICY PINPOLICY_DEFAULT
+#define PIV_PIN_WIRE_SIZE 8u
 
 #define TOUCHPOLICY_DEFAULT 0
 #define TOUCHPOLICY_NEVER 1
@@ -99,6 +100,15 @@ static uint8_t piv_default_pin_policy(uint8_t key_ref) {
     return PINPOLICY_ONCE;
 }
 
+static bool piv_reference_pair(const uint8_t **old_ref, const uint8_t **new_ref) {
+    if (apdu.nc != 2u * PIV_PIN_WIRE_SIZE) {
+        return false;
+    }
+    *old_ref = apdu.data;
+    *new_ref = apdu.data + PIV_PIN_WIRE_SIZE;
+    return true;
+}
+
 uint8_t piv_aid[] = {
     5,
     0xA0, 0x00, 0x00, 0x03, 0x8,
@@ -1291,20 +1301,23 @@ static int cmd_piv_change_pin(void) {
     if (P1(apdu) != 0x0 || (pin_ref != 0x80 && pin_ref != 0x81)) {
         return SW_REFERENCE_NOT_FOUND();
     }
+    const uint8_t *old_pin = NULL, *new_pin = NULL;
+    if (!piv_reference_pair(&old_pin, &new_pin)) {
+        return SW_INCORRECT_PARAMS();
+    }
     file_t *ef = file_search_by_fid(pin_ref == 0x80 ? EF_PIV_PIN : EF_PIV_PUK, NULL, SPECIFY_ANY);
     if (!ef) {
         return SW_MEMORY_FAILURE();
     }
-    uint8_t *pin_data = file_get_data(ef), pin_len = apdu.nc - pin_data[0];
-    uint16_t ret = check_pin(ef, apdu.data, pin_data[0]);
+    uint16_t ret = check_pin(ef, old_pin, PIV_PIN_WIRE_SIZE);
     if (ret != 0x9000) {
         return ret;
     }
 
     uint8_t dhash[34];
-    dhash[0] = pin_len;
+    dhash[0] = PIV_PIN_WIRE_SIZE;
     dhash[1] = 0x1; // Format
-    pin_derive_verifier(CONST_BYTE_ARRAY(apdu.data + pin_data[0], pin_len), dhash + 2);
+    pin_derive_verifier(CONST_BYTE_ARRAY(new_pin, PIV_PIN_WIRE_SIZE), dhash + 2);
     file_put_data(ef, CONST_BYTE_ARRAY(dhash, sizeof(dhash)));
     flash_commit();
     return SW_OK();
@@ -1314,19 +1327,22 @@ static int cmd_piv_reset_retry(void) {
     if (P1(apdu) != 0x0 || P2(apdu) != 0x80) {
         return SW_REFERENCE_NOT_FOUND();
     }
+    const uint8_t *old_puk = NULL, *new_pin = NULL;
+    if (!piv_reference_pair(&old_puk, &new_pin)) {
+        return SW_INCORRECT_PARAMS();
+    }
     file_t *ef = file_search_by_fid(EF_PIV_PUK, NULL, SPECIFY_ANY);
     if (!ef) {
         return SW_MEMORY_FAILURE();
     }
-    uint8_t *puk_data = file_get_data(ef), pin_len = apdu.nc - puk_data[0];
-    uint16_t ret = check_pin(ef, apdu.data, puk_data[0]);
+    uint16_t ret = check_pin(ef, old_puk, PIV_PIN_WIRE_SIZE);
     if (ret != 0x9000) {
         return ret;
     }
     uint8_t dhash[34];
-    dhash[0] = pin_len;
+    dhash[0] = PIV_PIN_WIRE_SIZE;
     dhash[1] = 0x1; // Format
-    pin_derive_verifier(CONST_BYTE_ARRAY(apdu.data + puk_data[0], pin_len), dhash + 2);
+    pin_derive_verifier(CONST_BYTE_ARRAY(new_pin, PIV_PIN_WIRE_SIZE), dhash + 2);
     ef = file_search_by_fid(EF_PIV_PIN, NULL, SPECIFY_ANY);
     file_put_data(ef, CONST_BYTE_ARRAY(dhash, sizeof(dhash)));
     pin_reset_retries(ef, true);
diff --git a/tests/piv/test_060_regressions.py b/tests/piv/test_060_regressions.py
index bafb8d6..6a2c366 100644
--- a/tests/piv/test_060_regressions.py
+++ b/tests/piv/test_060_regressions.py
@@ -124,6 +124,11 @@ def test_piv_ec_import_requires_the_field_length(managed_piv):
         delete_key(managed_piv, slot)
 
 
+@pytest.mark.parametrize(("instruction", "p2"), ((0x24, 0x80), (0x24, 0x81), (0x2C, 0x80)))
+def test_piv_reference_changes_require_two_wire_blocks(piv, instruction, p2):
+    assert_apdu_error(lambda: piv.protocol.send_apdu(0, instruction, 0, p2, b"12345678"), SW.INCORRECT_PARAMETERS)
+
+
 def test_piv_card_authentication_key_is_pin_free_by_default(managed_piv):
     slot = SLOT.CARD_AUTH
     try: