Bluetooth: CSIP: Update documentation for CSIP crypto functions

The encryption functions should document the expect byte order of
inputs and the byte order of the outputs.

The sef and sdf functions were also using an older, and incorrect,
description of the input, as it only takes the LTK as per CSIP 1.0.0

Signed-off-by: Emil Gydesen <[email protected]>

Author: Thalley

subsys/bluetooth/audio/csip_crypto.h

@@ -22,9 +22,10 @@
  * used in RSIs - Used by the Coordinated Set Identification service and
  * profile.
  *
- * @param sirk  16 byte LS byte first SIRK
- * @param r     3 byte LS byte first random value
- * @param out   3 byte LS byte first output buffer
+ * @param sirk  16-byte SIRK in little-endian byte order.
+ * @param r     3-byte random value in little-endian byte order.
+ * @param out   3-byte output buffer in little-endian byte order.
+ *
  * @return int 0 on success, any other value indicates a failure.
  */
 int bt_csip_sih(const uint8_t sirk[BT_CSIP_SIRK_SIZE], uint8_t r[BT_CSIP_CRYPTO_PRAND_SIZE],
@@ -37,20 +38,18 @@ int bt_csip_sih(const uint8_t sirk[BT_CSIP_SIRK_SIZE], uint8_t r[BT_CSIP_CRYPTO_
  * with a key K. The value of K depends on the transport on which the pairing
  * between the client and the server was performed.
  *
- * If the pairing was performed on BR/EDR, K is equal to the Link Key shared by
- * the server and the client.
+ * If the pairing was performed on Basic Rate/Enhanced Data Rate (BR/EDR), K is equal to the
+ * Link Key shared by the server and the client.
  *    K = Link Key.
  *
- * If the pairing was performed on LE, the 64 LSBs of K correspond to the 64
- * LSBs of the IRK that the server sent to the client during the Phase 3
- * (Transport Specific Key Distribution) of the pairing procedure (see Volume 3,
- * Part H, Section 2.1 in [2]), and the 64 MSBs of K correspond to the 64 MSBs
- * of the LTK shared by the server and client. That is,
- *    K = LTK_64-127 || IRK_0-63
+ * If the pairing was performed on Bluetooth Low Energy (LE), K is equal to the LTK shared by the
+ * server and client. That is,
+ *    K = LTK
+ *
+ * @param k         16-byte key in little-endian byte order.
+ * @param sirk      16-byte unencrypted SIRK key in little-endian byte order.
+ * @param out_sirk  16-byte encrypted SIRK key in little-endian byte order.
  *
- * @param k         16-byte key.
- * @param sirk      The unencrypted SIRK.
- * @param out_sirk  The encrypted SIRK.
  * @return int 0 on success, any other value indicates a failure.
  */
 int bt_csip_sef(const uint8_t k[BT_CSIP_CRYPTO_KEY_SIZE], const uint8_t sirk[BT_CSIP_SIRK_SIZE],
@@ -63,20 +62,18 @@ int bt_csip_sef(const uint8_t k[BT_CSIP_CRYPTO_KEY_SIZE], const uint8_t sirk[BT_
  * with a key K. The value of K depends on the transport on which the pairing
  * between the client and the server was performed.
  *
- * If the pairing was performed on BR/EDR, K is equal to the Link Key shared by
- * the server and the client.
+ * If the pairing was performed on Basic Rate/Enhanced Data Rate (BR/EDR), K is equal to the
+ * Link Key shared by the server and the client.
  *    K = Link Key.
  *
- * If the pairing was performed on LE, the 64 LSBs of K correspond to the 64
- * LSBs of the IRK that the server sent to the client during the Phase 3
- * (Transport Specific Key Distribution) of the pairing procedure (see Volume 3,
- * Part H, Section 2.1 in [2]), and the 64 MSBs of K correspond to the 64 MSBs
- * of the LTK shared by the server and client. That is,
- *    K = LTK_64-127 || IRK_0-63
+ * If the pairing was performed on Bluetooth Low Energy (LE), K is equal to the LTK shared by the
+ * server and client. That is,
+ *    K = LTK
+ *
+ * @param k         16-byte key in little-endian byte order.
+ * @param sirk      16-byte encrypted SIRK in little-endian byte order.
+ * @param out_sirk  16-byte decrypted SIRK in little-endian byte order.
  *
- * @param k         16-byte key.
- * @param sirk      The encrypted SIRK.
- * @param out_sirk  The decrypted SIRK.
  * @return int 0 on success, any other value indicates a failure.
  */
 int bt_csip_sdf(const uint8_t k[BT_CSIP_CRYPTO_KEY_SIZE], const uint8_t enc_sirk[BT_CSIP_SIRK_SIZE],

subsys/bluetooth/audio/csip_internal.h

@@ -21,6 +21,7 @@
 
 struct bt_csip_sirk {
 	uint8_t type;
+	/* SIRK stored in little endian byte order. */
 	uint8_t value[BT_CSIP_SIRK_SIZE];
 } __packed;