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+@page certificates Certificates in Tor.
+
+We have, alas, several certificate types in Tor.
+
+The tor_x509_cert_t type represents an X.509 certificate. This document
+won't explain X.509 to you -- possibly, no document can. (OTOH, Peter
+Gutmann's "x.509 style guide", though severely dated, does a good job of
+explaining how awful x.509 can be.)  Do not introduce any new usages of
+X.509. Right now we only use it in places where TLS forces us to do so.
+See x509.c for more information about using this type.
+
+
+The authority_cert_t type is used only for directory authority keys. It
+has a medium-term signing key (which the authorities actually keep
+online) signed by a long-term identity key (which the authority operator
+had really better be keeping offline).  Don't use it for any new kind of
+certificate.
+
+For new places where you need a certificate, consider tor_cert_t: it
+represents a typed and dated _something_ signed by an Ed25519 key.  The
+format is described in tor-spec. Unlike x.509, you can write it on a
+napkin.  The torcert.c file is used for manipulating these certificates and
+their associated keys.
+
+(Additionally, the Tor directory design uses a fairly wide variety of
+documents that include keys and which are signed by keys. You can
+consider these documents to be an additional kind of certificate if you
+want.)
+