Will it be possible to get SAN certificates?

Yes, that is going to be a readily available option in the client, and fully supported by the CA.

You’re encouraged to put as many names into a given SAN as you like. Boulder’s current default limit is something like 1000 (see “maxNames” in boulder-config.json), though Let’s Encrypt hasn’t announced their limit yet. Still, it’s probably going to be pretty big.

What are the limits at the X.509 level? Are there any additional limits from the Certification Policy or the Baseline Requirements?

The Baseline Requirements, version 1.3.0, section 7.1.4.2.1 only specify that the SAN exist and have the CN as an entry, there is no upper bound. RFC3280, section 4.2.1.7 defines it as a SEQUENCE SIZE (1..MAX) which means it’s implementation independent. For Firefox, for example, it appears that the max is not enforced so much the number of SAN entries, but rather the total size of the certificate. We may see compatibility issues if we try a huge SAN, but it’s probably easiest to find out by trying, and if it doesn’t work, asking the client to reissue two certs instead of one only takes a few minutes.

This would be a great area for community research. If someone can find out the max certificate sizes for various common clients (Firefox, Chrome, IE, Safari, Java, mobile browsers), the client can suggest a default size limit that will maximize compatibility.

I keep reading SAN and thinking you need a certificate for your storage-area network :sweat_smile:

I’d bet most TLS client implementations will parse quite a few SANs before failing, the real issue seems to be choosing a number that avoids unnecessarily bloating the size of the certificate itself. A good example here can be taken from Cloudflare who bundle SANs for their ‘Universal SSL’ service into a single certificate and seem to have a limit of ~47 SANs per cert.

Based on a quick test openssl with happily parse a cert with over 1000 SANs.

Unrelated to LE specifically: as @roland mentioned, having a huge certificate (with lots and lots of SAN entries) will — AFAIK — bloat the transfer size required for each SSL handshake, and will be bad for performance, so I wouldn’t really recommend that.

[image] joel: bloat the transfer size required for each SSL handshake, and will be bad for performance, so I wouldn't really recommend that. true indeed.. but that's what ECC 256bit SSL certs are good for too = smaller sizes :smiley:

subjectAltName Certificates

Issuance Policy

motoko January 12, 2016, 5:12am 16

Things can get a bit weird with some clients when the SAN field gets too big.

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subjectAltName Certificates

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