Constrain KeyUsage and ExtendedKeyUsage on both CA & EE certificates

RFC 6487 section 4.8.4 restricts the KeyUsage extension on EE
certificates to only be digitalSignature.

RFC 6487 section 4.8.5 forbids the ExtendedKeyUsage extension from
appearing on CA certificates. However, this may change in the future
through the standardisation process.

OK tb@

diff --git a/usr.sbin/rpki-client/cert.c b/usr.sbin/rpki-client/cert.c
index c6fcec3..cdd45e2 100644 (file)
--- a/usr.sbin/rpki-client/cert.c
+++ b/usr.sbin/rpki-client/cert.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: cert.c,v 1.91 2022/11/03 00:00:53 job Exp $ */
+/*     $OpenBSD: cert.c,v 1.92 2022/11/03 10:39:19 job Exp $ */
 /*
  * Copyright (c) 2022 Theo Buehler <tb@openbsd.org>
  * Copyright (c) 2021 Job Snijders <job@openbsd.org>
@@ -588,6 +588,18 @@ cert_parse_ee_cert(const char *fn, X509 *x)
        if ((p.res = calloc(1, sizeof(struct cert))) == NULL)
                err(1, NULL);
 
+       if (X509_get_key_usage(x) != KU_DIGITAL_SIGNATURE) {
+               warnx("%s: RFC 6487 section 4.8.4: KU must be digitalSignature",
+                   fn);
+               goto out;
+       }
+
+       /* EKU may be allowed for some purposes in the future. */
+       if (X509_get_extended_key_usage(x) != UINT32_MAX) {
+               warnx("%s: RFC 6487 section 4.8.5: EKU not allowed", fn);
+               goto out;
+       }
+
        index = X509_get_ext_by_NID(x, NID_sbgp_ipAddrBlock, -1);
        if ((ext = X509_get_ext(x, index)) != NULL) {
                if (!sbgp_ipaddrblk(&p, ext))
@@ -726,6 +738,14 @@ cert_parse_pre(const char *fn, const unsigned char *der, size_t len)
                            p.fn);
                        goto out;
                }
+
+               /* EKU may be allowed for some purposes in the future. */
+               if (X509_get_extended_key_usage(x) != UINT32_MAX) {
+                       warnx("%s: RFC 6487 section 4.8.5: EKU not allowed",
+                           fn);
+                       goto out;
+               }
+
                if (p.res->mft == NULL) {
                        warnx("%s: RFC 6487 section 4.8.8: missing SIA", p.fn);
                        goto out;