[PATCH 08/21] dpp-util: allow mutual auth in dpp_derive_ke

[James Prestwood <prestwoj@gmail.com>]

The Ke derivation requires an additional "L.x" value when
mutual authentication is used.
---
 src/dpp-util.c | 10 +++++++---
 src/dpp-util.h |  2 +-
 src/dpp.c      |  4 ++--
 3 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/src/dpp-util.c b/src/dpp-util.c
index d3171d02..0406a4dc 100644
--- a/src/dpp-util.c
+++ b/src/dpp-util.c
@@ -681,12 +681,13 @@ free_n:
 
 bool dpp_derive_ke(const uint8_t *i_nonce, const uint8_t *r_nonce,
 				struct l_ecc_scalar *m, struct l_ecc_scalar *n,
-				void *ke)
+				struct l_ecc_point *l, void *ke)
 {
 	uint8_t nonces[32 + 32];
 	size_t nonce_len;
 	uint64_t mx_bytes[L_ECC_MAX_DIGITS];
 	uint64_t nx_bytes[L_ECC_MAX_DIGITS];
+	uint64_t lx_bytes[L_ECC_MAX_DIGITS];
 	uint64_t bk[L_ECC_MAX_DIGITS];
 	ssize_t key_len;
 	enum l_checksum_type sha;
@@ -697,12 +698,15 @@ bool dpp_derive_ke(const uint8_t *i_nonce, const uint8_t *r_nonce,
 	nonce_len = dpp_nonce_len_from_key_len(key_len);
 	sha = dpp_sha_from_key_len(key_len);
 
+	if (l)
+		l_ecc_point_get_x(l, lx_bytes, key_len * 2);
+
 	memcpy(nonces, i_nonce, nonce_len);
 	memcpy(nonces + nonce_len, r_nonce, nonce_len);
 
 	/* bk = HKDF-Extract(I-nonce | R-nonce, M.x | N.x [ | L.x]) */
-	if (!hkdf_extract(sha, nonces, nonce_len * 2, 2, bk, mx_bytes,
-			key_len, nx_bytes, key_len))
+	if (!hkdf_extract(sha, nonces, nonce_len * 2, 3, bk, mx_bytes,
+			key_len, nx_bytes, key_len, lx_bytes, l ? key_len : 0))
 		return false;
 
 	/* ke = HKDF-Expand(bk, "DPP Key", length) */
diff --git a/src/dpp-util.h b/src/dpp-util.h
index 050d66cc..96711c35 100644
--- a/src/dpp-util.h
+++ b/src/dpp-util.h
@@ -176,7 +176,7 @@ struct l_ecc_scalar *dpp_derive_k2(const struct l_ecc_point *i_proto_public,
 				void *k2);
 bool dpp_derive_ke(const uint8_t *i_nonce, const uint8_t *r_nonce,
 				struct l_ecc_scalar *m, struct l_ecc_scalar *n,
-				void *ke);
+				struct l_ecc_point *l, void *ke);
 
 uint8_t *dpp_point_to_asn1(const struct l_ecc_point *p, size_t *len_out);
 struct l_ecc_point *dpp_point_from_asn1(const uint8_t *asn1, size_t len);
diff --git a/src/dpp.c b/src/dpp.c
index bbb27ff1..fc3d5c4f 100644
--- a/src/dpp.c
+++ b/src/dpp.c
@@ -1807,7 +1807,7 @@ static void authenticate_request(struct dpp_sm *dpp, const uint8_t *from,
 
 	l_getrandom(dpp->r_nonce, dpp->nonce_len);
 
-	if (!dpp_derive_ke(dpp->i_nonce, dpp->r_nonce, m, n, dpp->ke))
+	if (!dpp_derive_ke(dpp->i_nonce, dpp->r_nonce, m, n, NULL, dpp->ke))
 		goto auth_request_failed;
 
 	if (!dpp_derive_r_auth(dpp->i_nonce, dpp->r_nonce, dpp->nonce_len,
@@ -1983,7 +1983,7 @@ static void authenticate_response(struct dpp_sm *dpp, const uint8_t *from,
 		return;
 	}
 
-	if (!dpp_derive_ke(i_nonce, r_nonce, dpp->m, n, dpp->ke)) {
+	if (!dpp_derive_ke(i_nonce, r_nonce, dpp->m, n, NULL, dpp->ke)) {
 		l_debug("Failed to derive ke");
 		return;
 	}
-- 
2.25.1