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    • New comment by bobjonkman 29 November 2022
      @clacke Our #KWNPSA user group chatted with the #GetTogether developer a few months ago. He said demand for self-hosted G2G instances was minimal, and event interchange even more minimal. So #ActivityPub support on G2G has stalled, and he considers G2G more or less stable and mature.
    • New comment by bobjonkman 28 November 2022
      @lnxw48a1 ...then to Debian with a MATE desktop in 2020. Far less faffing about, finally being productive. Sometimes...
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    • New comment by bobjonkman 28 November 2022
      @lnxw48a1 I switched to Ubuntu-MATE when they insisted in the Unity desktop, then to Debiab
    • New comment by bobjonkman 28 November 2022
      @lnxw48a1 Ubuntu 22.04 has way too much reliance on snaps. Can't even get a regular install of Firefox, f'rinstance, only a snap.
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      bobjonkman favorited something by lnxw48a1: Oh, look! Evan has his own #Mastodon server now. https://prodromou.pub/@evan
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      RT @lnxw48a1 Oh, look! Evan has his own #Mastodon server now. https://prodromou.pub/@evan
    • New note by bobjonkman 30 September 2022
      That "aura" around bright objects is what I saw when I first got a cataract (clouding of the lens). It wasn't bad at first, and only in one eye, so I let it go until my vision was totally obscured in that eye. Don't do that. Get your eyes checked, and maybe a referral to […]
    • Favorite 30 September 2022
      bobjonkman favorited something by hypolite: Ok, that’s what I thought, thank you for the explanations. When I wear the new glasses, anything beyond a couple of feet is doubled until my eyes adjust which takes more time than with my current glasses, and then it still is almost imperceptibly blurry, although the comparison between the […]

The cost of long GnuPG/PGP keys

Posted by Bob Jonkman on March 25th, 2014

Never Eat That Green Food At The Back Of The Fridge

Never Trust Anyone Over Thirty

and

Never Sign A GnuPG/PGP Key That’s Older Than You Are

Face peeking into fridge

Looking for green food at the back of the fridge

OK, only one of those is true, and it’s not the last one. At the University of Waterloo Keysigning Party last fall, some of the people signing my key were younger than the key they were signing!

At the keysigning I was having a discussion with someone about key lengths. In particular, choosing 4096 bits instead of 2048. I was reading that GnuPG has a limit of 4096 bits, but that 4096 should be enough for all time to come.

I’ve read online that GnuPG does actually support larger key sizes but that there is a const in the source code limiting it to 4096. The reasons for doing so are supposedly speed, 4096 would be very slow to generate and use, and comparability with other implementations that may not support larger keys. Personally I think it’s an inevitability that this will be increased in time but we’re not there yet.

In 1996 when I started with PGP a 1024 bit key was considered adequate, by 1999 a 2048 bit key was still considered large.

Consider Moore’s Law: every 18 months computing capacity doubles and costs halve. I’m not sure if that means that over 18 months x flops increases to 2x flops at the same price, or that in 18 months the cost of x flops is half of today’s cost, or if it means that in 18 months the cost of 2x flops will be half the cost of x flops today. If the latter, then today’s x flops/$ is x/4 flops/$ in 18 months. That factor of four is an increase of two bits every 18 months, or four bits every 3 years.

So, the cost in 1996 to brute-force crack a 1024 bit key is the same as the cost in 1999 to crack a 1028 bit key. And in 2014, 18 years later, it’s the same cost as cracking a 1048 bit key (an additional 24 bits).

An increase in key size from 1024 bits to 2048 bits buys an additional 768 years of Moore’s Law. And going from 2048 bits to 4096 bits buys an additional 1536 years of Moore’s Law.

Is Moore’s Law overestimating the cost of cracking keys? Are there fundamental advances in math that have dropped the cost of cracking 1024 bit keys to near-zero? What’s the economic justification for crippling keysizes in GnuPG, anyway?

–Bob, who is not trolling but really wants to know.

Day 57 / 365 – refrigerator by Jason Rogers is used under a CC BYCC BY license.

This post is based on a message to the KWCrypto Mailing List.

 
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