The LE packet signing algorythm is based on RFC-4493, and is
used by the GATT procedure Write Signed Command. This implementation
is self contained, takes as inputs a Packet to be signed, a Serial
number, and CSRK, all in Network order. It's output is a fully
signed datagram for Transmission or Verification.
Signed-off-by: Brian Gix <bgix@xxxxxxxxxxxxxx>
---
include/net/bluetooth/smp.h | 3 +-
net/bluetooth/smp.c | 103 +++++++++++++++++++++++++++++++++++++++++++
2 files changed, 105 insertions(+), 1 deletions(-)
diff --git a/include/net/bluetooth/smp.h b/include/net/bluetooth/smp.h
index 15b97d5..987a864 100644
--- a/include/net/bluetooth/smp.h
+++ b/include/net/bluetooth/smp.h
@@ -134,7 +134,8 @@ struct smp_chan {
int smp_conn_security(struct l2cap_conn *conn, __u8 sec_level);
int smp_sig_channel(struct l2cap_conn *conn, struct sk_buff *skb);
int smp_distribute_keys(struct l2cap_conn *conn, __u8 force);
-
+int smp_sign_pkt(u8 *src, int slen, u8 *dst, int *dlen, __le32 serial,
+ u8 *csrk);
void smp_chan_destroy(struct l2cap_conn *conn);
#endif /* __SMP_H */
diff --git a/net/bluetooth/smp.c b/net/bluetooth/smp.c
index 0b96737..d53dbe4 100644
--- a/net/bluetooth/smp.c
+++ b/net/bluetooth/smp.c
@@ -30,6 +30,17 @@
#define SMP_TIMEOUT 30000 /* 30 seconds */
+static inline void lshift128(u8 target[16])
+{
+ int i;
+ for (i = 0; i < 15; i++) {
+ target[i] <<= 1;
+ if (target[i+1] & 0x80)
+ target[i] |= 0x01;
+ }
+ target[15] <<= 1;
+}
+
static inline void swap128(u8 src[16], u8 dst[16])
{
int i;
@@ -145,6 +156,98 @@ static int smp_rand(u8 *buf)
return 0;
}
+int smp_sign_pkt(u8 *src, int slen, u8 *dst, int *dlen, __le32 serial, u8 *csrk)
+{
+ struct crypto_blkcipher *tfm;
+ u8 k[16], sub_k[16], tmp[16];
+ int test_msb, i, err, enc_size = slen + sizeof(u32);
+ u32 serial_num = le32_to_cpu(serial);
+
+ if (!src || !dst || !csrk || !dlen || !slen || *dlen < enc_size + 8)
+ return -EINVAL;
+
+ tfm = crypto_alloc_blkcipher("ecb(aes)", 0, CRYPTO_ALG_ASYNC);
+ if (IS_ERR(tfm))
+ return -ENOTSUPP;
+
+ /* Put key into required order (Big Endian) */
+ swap128(csrk, k);
+
+ /* Calculate SubKey per RFC-4493 section 2.3 Step 1 */
+ memset(sub_k, 0, sizeof(sub_k));
+ err = smp_e(tfm, k, sub_k);
+ if (err) {
+ BT_ERR("SubKey generation failed: %d", err);
+ goto error;
+ }
+
+ /* Calculate K1 per RFC-4493 section 2.3 Step 2 */
+ test_msb = sub_k[0] & 0x80;
+ lshift128(sub_k);
+ if (test_msb)
+ sub_k[15] ^= 0x87;
+
+ /* Calculate K2 per RFC-4493 section 2.3 Step 3 (if needed) */
+ if (enc_size % 16) {
+ test_msb = sub_k[0] & 0x80;
+ lshift128(sub_k);
+ if (test_msb)
+ sub_k[15] ^= 0x87;
+ }
+
+ /* Stage data for encryption in dst buffer (Big Endian) */
+ put_unaligned_be32(serial_num, dst);
+ for (i = 0; i < slen; i++)
+ dst[i + sizeof(u32)] = src[slen - i - 1];
+
+
+ /* Apply blocks 1 to N-1 and Encrypt per RFC-4493 section 2.4 */
+ memset(tmp, 0, 16);
+ for (i = 0; i < enc_size - 16; i += 16) {
+ u128_xor((u128 *) tmp, (u128 *) tmp, (u128 *) &dst[i]);
+ err = smp_e(tfm, k, tmp);
+ if (err) {
+ BT_ERR("mid block(%d) encryption failed: %d", i, err);
+ goto error;
+ }
+ }
+
+ /* Apply SubKey for last block */
+ u128_xor((u128 *) tmp, (u128 *) tmp, (u128 *) sub_k);
+
+ /* Apply last block, and pad as needed */
+ if (enc_size % 16) {
+ /* reuse sub_k to pad target data to 16 bytes */
+ memset(sub_k, 0, 16);
+ memcpy(sub_k, &dst[i], enc_size - i);
+ sub_k[enc_size - i] = 0x80;
+
+ u128_xor((u128 *) tmp, (u128 *) tmp, (u128 *) sub_k);
+ } else {
+ u128_xor((u128 *) tmp, (u128 *) tmp, (u128 *) &dst[i]);
+ }
+
+ /* Encrypt last block */
+ err = smp_e(tfm, k, tmp);
+ if (err) {
+ BT_ERR("last block encryption failed: %d", err);
+ goto error;
+ }
+
+ /* Signature calculation complete */
+ swap128(tmp, k);
+
+ /* Construct final dst buffer (Little Endian) */
+ memcpy(dst, src, slen);
+ put_unaligned_le32(serial_num, &dst[slen]);
+ memcpy(&dst[slen + sizeof(u32)], &k[8], 8);
+ *dlen = slen + sizeof(u32) + 8;
+
+error:
+ crypto_free_blkcipher(tfm);
+ return err;
+}
+
static struct sk_buff *smp_build_cmd(struct l2cap_conn *conn, u8 code,
u16 dlen, void *data)
{
--
1.7.8
--
Brian Gix
bgix@xxxxxxxxxxxxxx
Employee of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum
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