read/write chunks in short length SM APDUs

npa/src/npa/iso-sm.h

@@ -30,6 +30,20 @@
 extern "C" {
 #endif
 
+/** @brief maximum length of response when targeting a SM RAPDU
+ *
+ * Using SM with authenticated data+le and encrypted data this is the biggest
+ * amount of the unencrypted response data we can receive. We assume AES block
+ * length for padding and MAC. */
+#define MAX_SM_APDU_RESP_SIZE 223
+
+/** @brief maximum length of data when targeting a SM APDU
+ *
+ * Using SM with authenticated data+header and encrypted data this is the
+ * biggest amount of the unencrypted data we can send. We assume AES block
+ * length for padding and MAC. */
+#define MAX_SM_APDU_DATA_SIZE 239
+
 /** @brief Padding indicator: use ISO/IEC 9797-1 padding method 2 */
 #define SM_ISO_PADDING 0x01
 /** @brief Padding indicator: use no padding */

npa/src/scutil.c

@@ -148,16 +148,13 @@ int print_avail(int verbose)
     return r;
 }
 
-#define maxresp SC_MAX_APDU_BUFFER_SIZE - 2
 #define ISO_READ_BINARY  0xB0
 #define ISO_P1_FLAG_SFID 0x80
 int read_binary_rec(sc_card_t *card, unsigned char sfid,
         u8 **ef, size_t *ef_len)
 {
     int r;
-    /* we read less bytes than possible. this is a workaround for acr 122,
+    size_t read = MAX_SM_APDU_RESP_SIZE;
-     * which only supports apdus of max 250 bytes */
-    size_t read = maxresp - 8;
     sc_apdu_t apdu;
     u8 *p;
 
@@ -222,9 +219,7 @@ int write_binary_rec(sc_card_t *card, unsigned char sfid,
         u8 *ef, size_t ef_len)
 {
     int r;
-    /* we write less bytes than possible. this is a workaround for acr 122,
+    size_t write = MAX_SM_APDU_DATA_SIZE, wrote = 0;
-     * which only supports apdus of max 250 bytes */
-    size_t write = maxresp - 8, wrote = 0;
     sc_apdu_t apdu;
     struct iso_sm_ctx *iso_sm_ctx = card->sm_ctx.info.cmd_data;