+/* --- Symmetric message authentication --- */
+
+typedef struct mac_ctx {
+ sig s;
+ const gcmac *mc;
+ gmac *m;
+ key_packdef kp;
+ key_bin kb;
+} mac_ctx;
+
+static sig *mac_init(key *k, void *kd, const gchash *hc)
+{
+ mac_ctx *m;
+ dstr d = DSTR_INIT;
+ int err;
+ const char *mm;
+
+ m = CREATE(mac_ctx);
+
+ key_fulltag(k, &d);
+ m->kp.e = KENC_BINARY;
+ m->kp.p = &m->kb;
+ m->kp.kd = 0;
+
+ if ((mm = key_getattr(0 /*yik*/, k, "mac")) == 0) {
+ dstr_putf(&d, "%s-hmac", hc->name);
+ mm = d.buf;
+ }
+ if ((m->mc = gmac_byname(mm)) == 0)
+ die(EXIT_FAILURE, "unknown message authentication scheme `%s'", mm);
+ dstr_reset(&d);
+
+ if ((err = key_unpack(&m->kp, kd, &d)) != 0) {
+ die(EXIT_FAILURE, "failed to unpack symmetric key `%s': %s",
+ d.buf, key_strerror(err));
+ }
+ dstr_destroy(&d);
+
+ if (keysz(m->kb.sz, m->mc->keysz) != m->kb.sz) {
+ die(EXIT_FAILURE, "bad key size %lu for `%s'",
+ (unsigned long)m->kb.sz, m->mc->name);
+ }
+ m->m = GM_KEY(m->mc, m->kb.k, m->kb.sz);
+ m->s.h = GM_INIT(m->m);
+ return (&m->s);
+}
+
+static int mac_sigdoit(sig *s, dstr *d)
+{
+ mac_ctx *m = (mac_ctx *)s;
+
+ dstr_ensure(d, m->mc->hashsz);
+ GH_DONE(m->s.h, d->buf);
+ d->len += m->mc->hashsz;
+ return (0);
+}
+
+static int mac_vrfdoit(sig *s, dstr *d)
+{
+ mac_ctx *m = (mac_ctx *)s;
+ const octet *t;
+
+ t = GH_DONE(m->s.h, 0);
+ if (d->len != m->mc->hashsz || memcmp(d->buf, t, d->len) != 0)
+ return (-1);
+ return (0);
+}
+
+static const char *mac_check(sig *s) { return (0); }
+
+static void mac_destroy(sig *s)
+{
+ mac_ctx *m = (mac_ctx *)s;
+ GM_DESTROY(m->m);
+ key_unpackdone(&m->kp);
+}
+
+static const sigops mac_sig = {
+ 0, 0,
+ mac_init, mac_sigdoit, mac_check, mac_destroy
+};
+
+static const sigops mac_vrf = {
+ 0, 0,
+ mac_init, mac_vrfdoit, mac_check, mac_destroy
+};
+