Tim Burke 5a4d3bdfc4 tempurl: Make the digest algorithm configurable ...

... and add support for SHA-256 and SHA-512 by default. This allows us
to start moving toward replacing SHA-1-based signatures. We've known
this would eventually be necessary for a while [1], and earlier this
year we've seen SHA-1 collisions [2].

Additionally, allow signatures to be base64-encoded, provided they start
with a digest name followed by a colon. Trailing padding is optional for
base64-encoded signatures, and both normal and "url-safe" modes are
supported. For example, all of the following SHA-1 signatures are
equivalent:

   da39a3ee5e6b4b0d3255bfef95601890afd80709
   sha1:2jmj7l5rSw0yVb/vlWAYkK/YBwk=
   sha1:2jmj7l5rSw0yVb/vlWAYkK/YBwk
   sha1:2jmj7l5rSw0yVb_vlWAYkK_YBwk=
   sha1:2jmj7l5rSw0yVb_vlWAYkK_YBwk

(Note that "normal" base64 encodings will require that you url encode
all "+" characters as "%2B" so they aren't misinterpretted as spaces.)

This was done for two reasons:

   1. A hex-encoded SHA-512 is rather lengthy at 128 characters -- 88
      isn't *that* much better, but it's something.
   2. This will allow us to more-easily add support for different
      digests with the same bit length in the future.

Base64-encoding is required for SHA-512 signatures; hex-encoding is
supported for SHA-256 signatures so we aren't needlessly breaking from
what Rackspace is doing.

[1] https://www.schneier.com/blog/archives/2012/10/when_will_we_se.html
[2] https://security.googleblog.com/2017/02/announcing-first-sha1-collision.html

Change-Id: Ia9dd1a91cc3c9c946f5f029cdefc9e66bcf01046
Related-Bug: #1733634

2018-01-31 02:19:18 +00:00

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