I have a private CA which provides certificates for three types of IoT devices (Type1, Type2 and Type3). On the IoT device certificate's subject DN, which attribute can be used for specifying this type information? Is there any existing use cases similar to this?

PS: CN field contains the device identifier. Looking on just the identifier, one cannot obtain the type information. Hence I have to provide the type info in a separate attribute.

1 Answer 1


That depends on the software that will check the certificate. If that is under your control and especially if you (or your colleagues) are developing it, then you can simply pick any attribute. However, picking something like Country would be rather unconventional.

While there are a long list of possible attributed defined for X.509 certificates, you are probably best restricting to the most common ones especially if you want to reference them by name instead of OID. Many of these relate to personal names/titles and geographical addresses and reattributing these to your use would be odd. Of all of them, the Organisational Unit attributes is probably the best for your use case.

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