add functions to calculate the CRC of an ISO14443-A message

Change-Id: I1ccd9885746a6044f298d7d531a9bc009a70288e
Reviewed-on: https://code.wireshark.org/review/13802
Petri-Dish: Martin Kaiser <wireshark@kaiser.cx>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Anders Broman <a.broman58@gmail.com>

2 files changed, 14 insertions, 0 deletions

diff --git a/wsutil/crc16.c b/wsutil/crc16.c
index 8febfa1c66..2ff576c200 100644
--- a/wsutil/crc16.c
+++ b/wsutil/crc16.c
@@ -346,6 +346,14 @@ guint16 crc16_ccitt_seed(const guint8 *buf, guint len, guint16 seed)
        ^ crc16_ccitt_xorout;
 }
 
+/* ISO14443-3, section 6.2.4: For ISO14443-A, the polynomial 0x1021 is
+   used, the initial register value shall be 0x6363, the final register
+   value is not XORed with anything. */
+guint16 crc16_iso14443a(const guint8 *buf, guint len)
+{
+    return crc16_reflected(buf,len, 0x6363 ,crc16_ccitt_table_reverse);
+}
+
 guint16 crc16_0x5935(const guint8 *buf, guint32 len, guint16 seed)
 {
     return crc16_unreflected(buf, len, seed, crc16_precompiled_5935);
diff --git a/wsutil/crc16.h b/wsutil/crc16.h
index 151b3f210d..11616089cc 100644
--- a/wsutil/crc16.h
+++ b/wsutil/crc16.h
@@ -61,6 +61,12 @@ WS_DLL_PUBLIC guint16 crc16_x25_ccitt_seed(const guint8 *buf, guint len, guint16
  @return The CRC16 CCITT checksum (using the given seed). */
 WS_DLL_PUBLIC guint16 crc16_ccitt_seed(const guint8 *buf, guint len, guint16 seed);
 
+/** Compute the 16bit CRC_A value of a buffer as defined in ISO14443-3.
+ @param buf The buffer containing the data.
+ @param len The number of bytes to include in the computation.
+ @return the CRC16 checksum for the buffer */
+WS_DLL_PUBLIC guint16 crc16_iso14443a(const guint8 *buf, guint len);
+
 /** Calculates a CRC16 checksum for the given buffer with the polynom
  *  0x5935 using a precompiled CRC table
  * @param buf a pointer to a buffer of the given length