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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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    Colm MacCárthaigh‏ @colmmacc 27 Feb 2019
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    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.

    8:32 PM - 27 Feb 2019
    • 6 Retweets
    • 92 Likes
    • Christopher Friedt John Coons Dov Murik Tim O’Hare Brian who survived a powerline Gus Politano HydroxyCoreyQuinn Ronil Mokashi Rukshani Athapathu
    11 replies 6 retweets 92 likes
      1. New conversation
      2. Mike Malone‏ @mjmalone 28 Feb 2019
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        Replying to @colmmacc

        My goto for roughly explaining is bringing it back to xor & hash functions & RNGs: goal is to get a long enough random number to xor with your cleartext. Block cipher stretches entropy by repeated hashing. Stream cipher by seeding a RNG.

        2 replies 0 retweets 1 like
      3. Mike Malone‏ @mjmalone 28 Feb 2019
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        Replying to @mjmalone @colmmacc

        I think it’s also worth elaborating on your point that “we all use symmetric crypto”. Like, I think that most people would be surprised to learn that TLS only uses asymmetric crypto for authn, and that encryption is done with a negotiated symmetric key.

        0 replies 0 retweets 2 likes
      4. End of conversation
      1. Abby Fuller‏ @abbyfuller 27 Feb 2019
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        Replying to @colmmacc

        yesssss

        0 replies 0 retweets 2 likes
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      1. Jake Rullman‏ @jakerullman 27 Feb 2019
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        Replying to @colmmacc

        What can we do to make it less baffling?

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      1. Anecdatabasis‏ @robinalangolden 27 Feb 2019
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        Replying to @colmmacc

        Well, now, you have to talk about the value of IVs, padding and stream vs block chaining. Is it safe to skip why inventing your own symmetric crypto scheme is a bad idea, and more so DES and 3DES? I’ve seen soo many custom ‘secure’ crypto schemes in the wild. 🥶

        0 replies 0 retweets 1 like
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      1. Steve Chalmers‏ @FStevenChalmers 27 Feb 2019
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        Replying to @colmmacc

        Consider discussing 3 or 4 "red team" type points, such as why keys have to be rotated in communications, why just simply encrypting large amounts of stored data with a single symmetric key is vulnerable, why an attacker will look for weaknesses in key handling etc first, etc

        0 replies 0 retweets 1 like
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      1. Steve Chalmers‏ @FStevenChalmers 27 Feb 2019
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        Replying to @colmmacc

        Oh, and part of why it's baffling is I can't ever get the precise definition of the mathematical notation used to describe the cryptography itself straight in my head. I can't translate that notation to badly written code, nor translate code back to that notation.

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      1. Tim Bray‏Verified account @timbray 1 Mar 2019
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        Replying to @colmmacc

        It'd be nice to cover symmetric vs asymmetric.

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      1. Daniel Bechaz‏ @DanielDynisious 28 Feb 2019
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        Replying to @colmmacc

        How can I "average human" use cryptography i.e. are there user tools that let me protect myself without a degree to understand it.

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      1. John Culkin‏ @jculkin 28 Feb 2019
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        Replying to @colmmacc

        How about a post on /r/aws? :-)

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