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4.1.3 Raw public-keys

There are situations in which a rather large certificate / certificate chain is undesirable or impractical. An example could be a resource constrained sensor network in which you do want to use authentication of and encryption between your devices but where your devices lack loads of memory or processing power. Furthermore, there are situations in which you don’t want to or can’t rely on a PKIX. TLS is, next to a PKIX environment, also commonly used with self-signed certificates in smaller deployments where the self-signed certificates are distributed to all involved protocol endpoints out-of-band. This practice does, however, still require the overhead of the certificate generation even though none of the information found in the certificate is actually used.

With raw public-keys, only a subset of the information found in typical certificates is utilized: namely, the SubjectPublicKeyInfo structure (in ASN.1 format) of a PKIX certificate that carries the parameters necessary to describe the public-key. Other parameters found in PKIX certificates are omitted. By omitting various certificate-related structures, the resulting raw public-key is kept fairly small in comparison to the original certificate, and the code to process the keys can be simpler.

It should be noted however, that the authenticity of these raw keys must be verified by an out-of-band mechanism or something like TOFU.