keyboxd: Allow import of v0 certificates.

* kbx/backend-support.c (be_is_x509_blob): Loose detection.
--

Here is a sample v0 cert:

-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----

kbx/backend-support.c

@@ -207,6 +207,7 @@ be_is_x509_blob (const unsigned char *blob, size_t bloblen)
    *  SEQUENCE    SEQUENCE    [0]   INTEGER  INTEGER
    *              (tbs)            (version) (s/n)
    *
+   *  Note that v0 certificates don't have an explict version number.
    */
 
   p = blob;
@@ -226,7 +227,11 @@ be_is_x509_blob (const unsigned char *blob, size_t bloblen)
   if (parse_ber_header (&p, &n, &class, &tag, &cons, &ndef, &objlen, &hdrlen))
     return 0; /* Not a proper BER object.  */
   if (!(class == CLASS_CONTEXT && tag == 0 && cons))
-    return 0; /* No context tag.  */
+    {
+      if (class == CLASS_UNIVERSAL && tag == TAG_INTEGER && !cons)
+        return 1; /* Might be a X.509 v0 cert with implict version.  */
+      return 0; /* No context tag.  */
+    }
 
   if (parse_ber_header (&p, &n, &class, &tag, &cons, &ndef, &objlen, &hdrlen))
     return 0; /* Not a proper BER object.  */