[tor-bugs] #7419 [Tor]: Choose a faster memwipe implementation

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#7419: Choose a faster memwipe implementation
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 Reporter:  nickm                   |          Owner:
     Type:  enhancement             |         Status:  needs_review
 Priority:  Medium                  |      Milestone:  Tor: 0.2.???
Component:  Tor                     |        Version:
 Severity:  Normal                  |     Resolution:
 Keywords:  tor-relay, nickm-patch  |  Actual Points:
Parent ID:                          |         Points:
  Sponsor:                          |
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Comment (by teor):

 Replying to [comment:19 logan]:
 > Here's a patch that checks if the platform supports explicit_bzero().
 Tested on OpenBSD.
 >
 > PASS: src/test/test-memwipe

 Replying to [comment:19 logan]:
 > Here's a patch that checks if the platform supports explicit_bzero().
 Tested on OpenBSD.
 >
 > PASS: src/test/test-memwipe

 There are multiple changes suggested in this ticket:

 nickm's original branch better_memwipe attempted to avoid using
 OpenSSL_cleanse for performance reasons by checking if a simple memset
 worked. I was happy to see it merged, but we never did because there was
 no evidence that performance was an issue.

 The attached explicit_bzero has better semantics than OpenSSL_cleanse, and
 is faster. Let's merge it.

 As discussed on IRC, we can also use memset_s on platforms that support it
 (NetBSD, OS X):

 So we can do the following:
 * if memset_s is supported:
   * call memset_s to wipe the memory and set the bytes
 * if explicit_bzero is supported:
   * call explicit_bzero to wipe the memory
   * call memset to set the bytes
 * otherwise:
   * call OpenSSL_cleanse to wipe the memory
   * call memset to set the bytes

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/7419#comment:21>
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