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  1. Jul 03, 2017
  2. Dec 05, 2016
    • Heikki Linnakangas's avatar
      Replace PostmasterRandom() with a stronger source, second attempt. · fe0a0b59
      Heikki Linnakangas authored
      This adds a new routine, pg_strong_random() for generating random bytes,
      for use in both frontend and backend. At the moment, it's only used in
      the backend, but the upcoming SCRAM authentication patches need strong
      random numbers in libpq as well.
      
      pg_strong_random() is based on, and replaces, the existing implementation
      in pgcrypto. It can acquire strong random numbers from a number of sources,
      depending on what's available:
      
      - OpenSSL RAND_bytes(), if built with OpenSSL
      - On Windows, the native cryptographic functions are used
      - /dev/urandom
      
      Unlike the current pgcrypto function, the source is chosen by configure.
      That makes it easier to test different implementations, and ensures that
      we don't accidentally fall back to a less secure implementation, if the
      primary source fails. All of those methods are quite reliable, it would be
      pretty surprising for them to fail, so we'd rather find out by failing
      hard.
      
      If no strong random source is available, we fall back to using erand48(),
      seeded from current timestamp, like PostmasterRandom() was. That isn't
      cryptographically secure, but allows us to still work on platforms that
      don't have any of the above stronger sources. Because it's not very secure,
      the built-in implementation is only used if explicitly requested with
      --disable-strong-random.
      
      This replaces the more complicated Fortuna algorithm we used to have in
      pgcrypto, which is unfortunate, but all modern platforms have /dev/urandom,
      so it doesn't seem worth the maintenance effort to keep that. pgcrypto
      functions that require strong random numbers will be disabled with
      --disable-strong-random.
      
      Original patch by Magnus Hagander, tons of further work by Michael Paquier
      and me.
      
      Discussion: https://www.postgresql.org/message-id/CAB7nPqRy3krN8quR9XujMVVHYtXJ0_60nqgVc6oUk8ygyVkZsA@mail.gmail.com
      Discussion: https://www.postgresql.org/message-id/CAB7nPqRWkNYRRPJA7-cF+LfroYV10pvjdz6GNvxk-Eee9FypKA@mail.gmail.com
      fe0a0b59
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