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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. Colm MacCárthaigh‏ @colmmacc 1 Mar 2019
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      Colm MacCárthaigh Retweeted Colm MacCárthaigh

      O.k., this is happening ... now. I'm going to explain what's actually going on when data is encrypted, hopefully without mystifying, oh and some of the weird and inconsistent stuff cryptographers come up with.https://twitter.com/colmmacc/status/1100976962846154752 …

      Colm MacCárthaigh added,

      Colm MacCárthaigh @colmmacc
      Prompted by some good questions, in the next few days I'm going to do a longer-than-usual tweet thread explainer on symmetric cryptography. That's the kind we all use for encrypting data. Are there things you've always been curious about? It's mostly baffling, so no shaming.
      14 replies 133 retweets 388 likes
      Show this thread
    2. Mike Malone‏ @mjmalone 1 Mar 2019
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      Replying to @colmmacc

      Awesome thread! One thing that helped my intuition about this stuff is: block ciphers (AES) take a small secret and "stretch" it to the length of your data using a hash function. Stream ciphers (ChaCha20) use an RNG.

      1 reply 0 retweets 1 like
    3. Mike Malone‏ @mjmalone 1 Mar 2019
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      Replying to @mjmalone @colmmacc

      If you know how hashes & RNGs work this explains some stuff. Like the need for an IV: if you seed with the same secret every time you'll produce the same random sequences.

      1 reply 0 retweets 1 like
    4. Mike Malone‏ @mjmalone 1 Mar 2019
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      Replying to @mjmalone @colmmacc

      Also explains (one reason) you need to re-seed periodically: pseudo-random number sequences become more predictable as you pull longer sequences from them.

      1 reply 0 retweets 1 like
    5. Colm MacCárthaigh‏ @colmmacc 1 Mar 2019
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      Replying to @mjmalone

      Well a few things to clear up :) I don't think the hash Vs RNG distinction is that meaningful. Many RNGs use hashes, for example HMAC_DRBG, which is one of the best RNGs (imo). It's all just algorithms to create successive streams of random data, with a balance for perf.

      2 replies 0 retweets 0 likes
      Colm MacCárthaigh‏ @colmmacc 1 Mar 2019
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      Replying to @colmmacc @mjmalone

      PRNGs don't quite become more predictable the more you pull from them. Some of them just straight up cycle after a certain point, so you have to cut-off before the period. But mostly it's about how much data would it take to reverse engineer the initial conditions.

      1:52 PM - 1 Mar 2019
      1 reply 0 retweets 0 likes
        1. Mike Malone‏ @mjmalone 1 Mar 2019
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          Replying to @colmmacc

          Rule of thumb I’ve heard is sqrt(period). Some CSPRNGs don’t have a closed form computable period though, but I think they usually have provable minimum bounds on period. Been a while.

          1 reply 0 retweets 0 likes
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