RFC 2797:Certificate Management Messages over CMS
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1. Protocol Requirements

   -  The protocol is to be based as much as possible on the existing
      CMS, PKCS#10 and CRMF specifications.
   -  The protocol must support the current industry practice of a
      PKCS#10 request followed by a PKCS#7 response as a subset of the
      protocol.
   -  The protocol needs to easily support the multi-key enrollment
      protocols required by S/MIME and other groups.
   -  The protocol must supply a way of doing all operations in a
      single-round trip.  When this is not possible the number of round
      trips is to be minimized.
   -  The protocol will be designed such that all key generation can
      occur on the client.
   -  The mandatory algorithms must superset the required algorithms for
      S/MIME.
   -  The protocol will contain POP methods. Optional provisions for
      multiple-round trip POP will be made if necessary.
   -  The protocol will support deferred and pending responses to
      certificate request for cases where external procedures are
      required to issue a certificate.
   -  The protocol needs to support arbitrary chains of local
      registration authorities as intermediaries between certificate
      requesters and issuers.

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