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colmmacc's profile
Colm MacCárthaigh
Colm MacCárthaigh
Colm MacCárthaigh
@colmmacc

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Colm MacCárthaigh

@colmmacc

AWS, Apache, Crypto, Irish Music, Haiku, Photography

Seattle
notesfromthesound.com
Joined April 2008

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    1. Matthew Green‏ @matthew_d_green 22 Nov 2017
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      These seem like really good mitigations to make a userland RNG safe. But makes me wonder why they don’t just use a kernel RNG.https://aws.amazon.com/blogs/opensource/better-random-number-generation-for-openssl-libc-and-linux-mainline/ …

      7 replies 15 retweets 27 likes
    2. Colm MacCárthaigh‏ @colmmacc 22 Nov 2017
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      Replying to @matthew_d_green

      Reason 1: speed, we (and OpenSSL, BoringSSL, etc ...) have per-thread RNGs to avoid lock contention (either in user-space or the kernel). Matters most for per-record explicit IVs and hello messages. Recent improvements in Linux and libc perf should fix this.

      2 replies 1 retweet 6 likes
    3. Colm MacCárthaigh‏ @colmmacc 22 Nov 2017
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      Replying to @colmmacc @matthew_d_green

      Reason 2: In-kernel RNGs have been their own poorly audited moving target, getting better though!

      2 replies 1 retweet 1 like
    4. Matthew Green‏ @matthew_d_green 22 Nov 2017
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      Replying to @colmmacc

      The third mitigation still seems to rely on kernel support, so it still seems like auditing and replacing the kernel RNG is in scope.

      1 reply 0 retweets 0 likes
    5. Colm MacCárthaigh‏ @colmmacc 22 Nov 2017
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      Replying to @matthew_d_green

      For now it's easier - Linux won't break a userspace guarantee, so madvise option is reliable, but an SP800-90A DRBG may come to Linux soon in the form of http://www.chronox.de/lrng.html  , http://www.chronox.de/lrng/doc/lrng.pdf …

      1 reply 0 retweets 1 like
    6. Matthew Green‏ @matthew_d_green 22 Nov 2017
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      Replying to @colmmacc

      I hope they do HMAC and not CTR. I think using invertible functions for RNGs is a dangerous idea. Too easy to break the rekeying logic and get a beautiful backdoor.

      1 reply 2 retweets 3 likes
    7. Colm MacCárthaigh‏ @colmmacc 22 Nov 2017
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      Replying to @matthew_d_green

      HMAC is considerably slower, even with SHA extensions, and Prediction Resistance is supposed to mitigate that, which is how all of the implementations so far have settled on AES_CTR or ChaCha20.

      2 replies 1 retweet 0 likes
    8. Matthew Green‏ @matthew_d_green 22 Nov 2017
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      Replying to @colmmacc

      The problem is that prediction resistance and rekeying are both easy to turn off, and then you get an undetectably broken PRG with efficient state recovery.

      1 reply 1 retweet 0 likes
    9. Matthew Green‏ @matthew_d_green 22 Nov 2017
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      Replying to @matthew_d_green @colmmacc

      This is a rarified concern but after Juniper and Fortinet I’ve come to assume that there are people deliberately screwing with (some) PRGs.

      1 reply 0 retweets 2 likes
      Colm MacCárthaigh‏ @colmmacc 22 Nov 2017
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      Replying to @matthew_d_green

      I'm curious what you think of this ... it's from SP800-90C and seems to defy the point of mixing in entropy and to allow a "Live Full Entropy Source" to bias/control the output with bit-for-bit effort. Seems odd to me.pic.twitter.com/PAmddbRLzV

      8:01 PM - 22 Nov 2017
      1 reply 0 retweets 0 likes
        1. Matthew Green‏ @matthew_d_green 22 Nov 2017
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          Replying to @colmmacc

          This looks like what Linux was going to do with the mixing of RDRAND and PRG output. Or are doing. Doesn’t make much sense.

          0 replies 0 retweets 0 likes
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