Make sure the signature also covers the session label.

diff --git a/doc/SPTPS b/doc/SPTPS
index 78927f6..2d8fee5 100644 (file)
--- a/doc/SPTPS
+++ b/doc/SPTPS
@@ -124,7 +124,7 @@ Remarks:
 - After receiving the other's SIG message, the signature is verified. If it is
   correct, the shared secret is calculated from the public keys exchanged in the
   KEX message using the Elliptic Curve Diffie-Helman algorithm.
-- The shared secret key is expanded using a PRF. Both nonces and an application
+- The shared secret key is expanded using a PRF. Both nonces and the application
   specific label are also used as input for the PRF.
 - An ACK message is sent only when doing key renegotiation, and is sent using
   the old encryption keys.
@@ -135,6 +135,7 @@ The signature is calculated over this string:
 - uint8_t initiator (0 = local peer, 1 = remote peer is initiator)
 - opaque remote_kex_message[1 + 32 + ECDH_SIZE]
 - opaque local_kex_message[1 + 32 + ECDH_SIZE]
+- opaque label[label_length]
 
 The PRF is calculated as follows:
 

diff --git a/src/sptps.c b/src/sptps.c
index 2449e7b..bdbfb89 100644 (file)
--- a/src/sptps.c
+++ b/src/sptps.c
@@ -159,13 +159,14 @@ static bool send_sig(sptps_t *s) {
        size_t keylen = ECDH_SIZE;
        size_t siglen = ecdsa_size(&s->mykey);
 
-       // Concatenate both KEX messages, plus tag indicating if it is from the connection originator
-       char msg[(1 + 32 + keylen) * 2 + 1];
+       // Concatenate both KEX messages, plus tag indicating if it is from the connection originator, plus label
+       char msg[(1 + 32 + keylen) * 2 + 1 + s->labellen];
        char sig[siglen];
 
        msg[0] = s->initiator;
        memcpy(msg + 1, s->mykex, 1 + 32 + keylen);
-       memcpy(msg + 2 + 32 + keylen, s->hiskex, 1 + 32 + keylen);
+       memcpy(msg + 1 + 33 + keylen, s->hiskex, 1 + 32 + keylen);
+       memcpy(msg + 1 + 2 * (33 + keylen), s->label, s->labellen);
 
        // Sign the result.
        if(!ecdsa_sign(&s->mykey, msg, sizeof msg, sig))
@@ -275,11 +276,12 @@ static bool receive_sig(sptps_t *s, const char *data, uint16_t len) {
                return error(s, EIO, "Invalid KEX record length");
 
        // Concatenate both KEX messages, plus tag indicating if it is from the connection originator
-       char msg[(1 + 32 + keylen) * 2 + 1];
+       char msg[(1 + 32 + keylen) * 2 + 1 + s->labellen];
 
        msg[0] = !s->initiator;
        memcpy(msg + 1, s->hiskex, 1 + 32 + keylen);
-       memcpy(msg + 2 + 32 + keylen, s->mykex, 1 + 32 + keylen);
+       memcpy(msg + 1 + 33 + keylen, s->mykex, 1 + 32 + keylen);
+       memcpy(msg + 1 + 2 * (33 + keylen), s->label, s->labellen);
 
        // Verify signature.
        if(!ecdsa_verify(&s->hiskey, msg, sizeof msg, data))