Log which elliptic curve we're using for ECDH kex.

It seems like quite an important thing to mention in the event log!
Suppose there's a bug affecting only one curve, for example? Fixed-
group Diffie-Hellman has always logged the group, but the ECDH log
message just told you the hash and not also the curve.

To implement this, I've added a 'textname' field to all elliptic
curves, whether they're used for kex or signing or both, suitable for
use in this log message and any others we might find a need for in
future.

ssh.c

@@ -6770,7 +6770,8 @@ static void do_ssh2_transport(Ssh ssh, const void *vin, int inlen,
         }
     } else if (ssh->kex->main_type == KEXTYPE_ECDH) {
 
-        logeventf(ssh, "Doing ECDH key exchange with hash %s",
+        logeventf(ssh, "Doing ECDH key exchange with curve %s and hash %s",
+                  ssh_ecdhkex_curve_textname(ssh->kex),
                   ssh->kex->hash->text_name);
         ssh->pkt_kctx = SSH2_PKTCTX_ECDHKEX;
 

ssh.h

@@ -134,7 +134,14 @@ struct ec_ecurve
 
 struct ec_curve {
     enum { EC_WEIERSTRASS, EC_MONTGOMERY, EC_EDWARDS } type;
-    const char *name;
+    /* 'name' is the identifier of the curve when it has to appear in
+     * wire protocol encodings, as it does in e.g. the public key and
+     * signature formats for NIST curves. Curves which do not format
+     * their keys or signatures in this way just have name==NULL.
+     *
+     * 'textname' is non-NULL for all curves, and is a human-readable
+     * identification suitable for putting in log messages. */
+    const char *name, *textname;
     unsigned int fieldBits;
     Bignum p;
     union {
@@ -210,6 +217,7 @@ void ssh_rsakex_encrypt(const struct ssh_hash *h, unsigned char *in, int inlen,
  * SSH2 ECDH key exchange functions
  */
 struct ssh_kex;
+const char *ssh_ecdhkex_curve_textname(const struct ssh_kex *kex);
 void *ssh_ecdhkex_newkey(const struct ssh_kex *kex);
 void ssh_ecdhkex_freekey(void *key);
 char *ssh_ecdhkex_getpublic(void *key, int *len);

sshecc.c

@@ -157,7 +157,7 @@ static struct ec_curve *ec_p256(void)
         };
 
         initialise_wcurve(&curve, 256, p, a, b, n, Gx, Gy);
-        curve.name = "nistp256";
+        curve.textname = curve.name = "nistp256";
 
         /* Now initialised, no need to do it again */
         initialised = 1;
@@ -223,7 +223,7 @@ static struct ec_curve *ec_p384(void)
         };
 
         initialise_wcurve(&curve, 384, p, a, b, n, Gx, Gy);
-        curve.name = "nistp384";
+        curve.textname = curve.name = "nistp384";
 
         /* Now initialised, no need to do it again */
         initialised = 1;
@@ -307,7 +307,7 @@ static struct ec_curve *ec_p521(void)
         };
 
         initialise_wcurve(&curve, 521, p, a, b, n, Gx, Gy);
-        curve.name = "nistp521";
+        curve.textname = curve.name = "nistp521";
 
         /* Now initialised, no need to do it again */
         initialised = 1;
@@ -352,6 +352,7 @@ static struct ec_curve *ec_curve25519(void)
         /* This curve doesn't need a name, because it's never used in
          * any format that embeds the curve name */
         curve.name = NULL;
+        curve.textname = "Curve25519";
 
         /* Now initialised, no need to do it again */
         initialised = 1;
@@ -403,6 +404,7 @@ static struct ec_curve *ec_ed25519(void)
         curve.name = NULL;
 
         initialise_ecurve(&curve, 256, q, l, d, Bx, By);
+        curve.textname = "Ed25519";
 
         /* Now initialised, no need to do it again */
         initialised = 1;
@@ -2704,6 +2706,13 @@ static Bignum ecdh_calculate(const Bignum private,
     return ret;
 }
 
+const char *ssh_ecdhkex_curve_textname(const struct ssh_kex *kex)
+{
+    const struct eckex_extra *extra = (const struct eckex_extra *)kex->extra;
+    struct ec_curve *curve = extra->curve();
+    return curve->textname;
+}
+
 void *ssh_ecdhkex_newkey(const struct ssh_kex *kex)
 {
     const struct eckex_extra *extra = (const struct eckex_extra *)kex->extra;