[tor-bugs] #26116 [Core Tor/Tor]: OpenSSL 1.1.1 changed the semantics of the password callback return value

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#26116: OpenSSL 1.1.1 changed the semantics of the password callback return value
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     Reporter:  nickm    |      Owner:  nickm
         Type:  defect   |     Status:  assigned
     Priority:  Medium   |  Milestone:  Tor: 0.3.4.x-final
    Component:  Core     |    Version:
  Tor/Tor                |   Keywords:  029-backport 031-backport
     Severity:  Normal   |  032-backport 033-backport
Actual Points:           |  Parent ID:
       Points:           |   Reviewer:
      Sponsor:           |
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 In c82c3462267afdbbaa5, openssl changed its interpretation of getting a
 "0" result from a PEM password callback.  Previously, this indicated an
 error, and the documentation said:

 >The callback '''must''' return the number of characters in the passphrase
 or 0 if an error occurred.

 But now, 0 means an empty passphrase, and -1 means that an error occurred.

 To avoid strange bugs and compatibility issues, we should have our
 pem_no_password_cb function return -1 instead. (-1 was always a supported
 return value, even if it isn't documented.)

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/26116>
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