[tor-bugs] #28839 [Core Tor/Tor]: Speed up parsing RSA onion keys from microdescriptors

[Tor Bug Tracker & Wiki]

#28839: Speed up parsing RSA onion keys from microdescriptors
------------------------------+---------------------------------
     Reporter:  nickm         |      Owner:  (none)
         Type:  defect        |     Status:  new
     Priority:  Medium        |  Milestone:  Tor: 0.4.0.x-final
    Component:  Core Tor/Tor  |    Version:  Tor: 0.3.4.9
     Severity:  Normal        |   Keywords:  startup performance
Actual Points:                |  Parent ID:  #28481
       Points:                |   Reviewer:
      Sponsor:  Sponsor8-can  |
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 The two functions `crypto_pk_read_public_key_from_string()` is about 9% of
 our startup time when we have directory information, and
 `router_set_rsa_onion_pkey()` is about 2.4%.  There is a probably a good
 chance to save time here, in a few ways:

   * Maybe pem_decode() could be faster. Right now it seems to be eating
 3.53% of the startup time, and most of its energy is going into
 tor_asprintf().

   * We possibly save a decode/encode cycle, since we are parsing asn1 into
 an RSA key, and then re-encoding that key into an asn1 string in
 router_set_rsa_onion_pkey().

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/28839>
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