PIV - Improved error handling of get_challenge

Random data from PIV card is obtained using GENERAL AUTHENTICATE command
for a request of a Challenge from the card. "00 87 00 9B 04 7C 02 81 00"
Usually 8 bytes are returned.

NIST 800-73-3_PART2, "A.1 Authentication of the PIV Card Application Administrator"
"Table 11. Authentication of PIV Card Application Administrator" shows an example of
how to do this.

Some cards (one I have: 3b:7d:96:00:00:80:31:80:65:b0:83:11:17:d6:83:00:90:00)
will not allow 2 of these commands in a row. (Maybe assuming command is only
used as in Table 11 and is expecting the second command.)

Code was added to card-piv.c so if "6A 80" is returned, try the command one more time.
For any other GENERAL AUTHENTICATE failure, SC_ERROR_NOT_SUPPORTED is returned.
piv_get_challenge may be called within a loop from sc_get_challenge if more random
data is needed thus causing the the 2 commands to sent in a row.

On branch piv-improved-matching
 Changes to be committed:
	modified:   card-piv.c

src/libopensc/card-piv.c

@@ -2277,6 +2277,22 @@ static int piv_get_challenge(sc_card_t *card, u8 *rnd, size_t len)
 
 	/* NIST 800-73-3 says use 9B, previous verisons used 00 */
 	r = piv_general_io(card, 0x87, 0x00, 0x9B, sbuf, sizeof sbuf, &rbuf, &rbuf_len);
+	/*
+	 * piv_get_challenge is called in a loop. 
+	 * some cards may allow 1 challenge expecting it to be part of 
+	 * NIST 800-73-3 part 2 "Authentication of PIV Card Application Administrator"
+	 * and return "6A 80" if last command was a get_challenge.
+	 * Now that the card returned error, we can try one more time.
+	 */
+	 if (r == SC_ERROR_INCORRECT_PARAMETERS) {
+		if (rbuf)
+			free(rbuf);
+		rbuf_len = 0;
+		r = piv_general_io(card, 0x87, 0x00, 0x9B, sbuf, sizeof sbuf, &rbuf, &rbuf_len);
+		if (r == SC_ERROR_INCORRECT_PARAMETERS) {
+			r = SC_ERROR_NOT_SUPPORTED;
+		}
+	}
 	LOG_TEST_GOTO_ERR(card->ctx, r, "GENERAL AUTHENTICATE failed");
 
 	p = rbuf;