X.509
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... defined term "CA-certificate" in X.509. Note that this term is not
to be confused with the X.500 "cACertificate" attribute type, which
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Note 1. This scheme does not make use of any of the X.509 v3
extensions as it must be able to work even for version 1
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... PKIX Working Group and are used to establish and maintain an
Internet X.509 PKI. There is no requirement for specific security
mechanisms ...