[tor-bugs] #27999 [Core Tor/Tor]: Allow for long-running signing operations

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#27999: Allow for long-running signing operations
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 Reporter:  ln5          |          Owner:  ln5
     Type:  enhancement  |         Status:  assigned
 Priority:  Medium       |      Component:  Core Tor/Tor
  Version:               |       Severity:  Normal
 Keywords:  TorHSM       |  Actual Points:
Parent ID:               |         Points:
 Reviewer:               |        Sponsor:
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 In order to be able to put secret keys used for signing status documents
 on an HSM device, which may require a long time(*) to finish, we need to
 allow for router_get_dirobj_signature() to return something akin to EAGAIN
 and make its callers able to cope with that.

 router_get_dirobj_signature() has only two callers, both with only one
 same caller (dirvote_act()) so that seems pretty contained. Question is if
 we should push this down a level to crypto_pk_private_sign() for other
 potential use cases than votes and consensuses only?

 (*) Let's define "a long time" as anything taking more than 1/10 of a
 second.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/27999>
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