On 12/31/18 2:21 PM, Viktor Dukhovni wrote:
On Dec 31, 2018, at 2:01 PM, zorion zorion@autistici.org wrote:
Ok, I had a hard time finding out what exactly the *trust-anchor* was supposed to be. I took a guess that it was the combined cert chain, but obviously that is not it.
A trust-anchor is any issuing CA you designate as trusted, and it does not have to be a root CA, it can also be any intermediate CA.
Thank you for the explanation!
What exactly is the trust-anchor? Is it the top level cert from the CA in the chain (#4 in your danecheck below)?
It is any of 2, 3 or 4. The important constraint with DANE-TA(2), as explained in https://tools.ietf.org/html/rfc7671#section-5.2.2, is that if you do choose a root CA as your trust-anchor, unlike the case in non-DANE PKIX protocols, it MUST be sent to the client along with the intermediate issuer certificates.
Would that be the smtp_tls_CAfile option in postfix? I've got an intermediate bundle that I provide to that option in main.cf
To compute the digest of a CA certificate, create a PEM file containing just that certificate. Or use my "chaingen" script (attached), which can process a complete chain of certificates, but DO NOT then publish all the TLSA records it outputs. Publish no more than one TLSA record per certificate in the chain, typically just the "3 1 1" for the EE cert, and "2 1 1" for the TA certs. And no need to match at every level. At most two trust anchors (typically just one) are enough.
Thanks! Is there a benefit for also publishing the "2 1 1" TA certs if I'm already publishing the "3 1 1" EE cert?
ps. accidentally only sent this directly to Viktor, sending it to the list.