Re: [Asrg] E-postage from first principles
Jonathan Morton <chromi@chromatix.demon.co.uk> Thu, 29 April 2004 19:42 UTC
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From: Jonathan Morton <chromi@chromatix.demon.co.uk>
Subject: Re: [Asrg] E-postage from first principles
To: John Levine <asrg@johnlevine.com>
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Date: Thu, 29 Apr 2004 18:58:57 +0100
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>>> Receipient rate limiting might take the form of hashcash, although >>> that seems too easily circumvented so long as the bad guys have >>> zombies to do their hashing. >> >> This is a quantitative rather than qualitative argument against >> hashcash, which is easily answered by increasing the bit count >> demanded >> by the recipient, if it seems it's not having enough effect. > > The problem is that if you increase the bit count demanded from the > bad guys, you also increase the bit count demanded from the good guys. > Since the bad guys have more computers at their disposal than the good > guys do, if you demand a big enough hash from the bad guys to deter > them, you're going to lock out the good guys altogether, e.g., demand > a hash from Aunt Sadie that will limit her 486 to one e-mail message a > week. > > You might want to demand larger hashes from bad guys from good guys, > but if you could tell which was which, you could reject the bad guys' > mail outright and dispense with the hashes. Note that SHA-1 is noticeably more computationally expensive on x86 than most RISC platforms (or, probably, AMD64), which automatically makes the present incarnation of hashcash biased against the current crop of Wintel zombies. As a point of comparison, it takes about 2500 cycles per hash on an Athlon-XP, versus only 1000 on a PowerPC G3 or G4. This has positive implications for third-party vendors - see below. I've partially worked out a scheme which offers two solutions to this problem: - Users with low-end machines (including handhelds) may buy hashcash tokens from a stand-alone third party vendor. This doesn't require the micropayment infrastructure that full-blown e-postage needs. Hashcash vendors need only recoup their own costs, thus a competitive market is easy to achieve without any need for regulation. - The stamp optionally includes a signature to facilitate whitelisting. This can reduce the hashcash demanded from regular correspondents to as low as 8 bits, which is computationally trivial - thus even low-end users will not normally need to buy tokens regularly. Unlike existing high-confidence schemes like PGP and S/MIME, it is only for reasonable-confidence identification of regular correspondents, and as such is considerably more lightweight and doesn't require anything of the message body. Can anyone shed some light on how many cycles a Z80 processor would take to handle a typical SHA-1 hash cycle? Since derivatives of the Z80 may still be used in a few of the lowest-end handhelds, I'd like to have a handle on how long it would take for it to generate the "computationally trivial" 8-bit hashcash token that the signature requires. If nobody happens to have a Z80 and a compiler to hand, I'll put in some work and try it for the 6502 instead - I have a handful of old BBC Micros lying around. -------------------------------------------------------------- from: Jonathan "Chromatix" Morton mail: chromi@chromatix.demon.co.uk website: http://www.chromatix.uklinux.net/ tagline: The key to knowledge is not to rely on people to teach you it. _______________________________________________ Asrg mailing list Asrg@ietf.org https://www1.ietf.org/mailman/listinfo/asrg
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- Re: [Asrg] (no subject) John Levine
- RE: [Asrg] (no subject) Hallam-Baker, Phillip
- Re: [Asrg] (no subject) Devdas Bhagat
- RE: [Asrg] (no subject) Hallam-Baker, Phillip
- Re: [Asrg] (no subject) Barry Shein
- RE: [Asrg] (no subject) Hallam-Baker, Phillip
- The end result of E-postage (was Re: [Asrg] (no s… Alan DeKok
- RE: [Asrg] (no subject) Barry Shein
- RE: [Asrg] (no subject) Hallam-Baker, Phillip
- RE: [Asrg] (no subject) Barry Shein
- Re: [Asrg] (no subject) Roger B.A. Klorese
- Re: [Asrg] (no subject) Barry Shein
- Re: [Asrg] (no subject) "Roger B.A. Klorese "
- [Asrg] E-postage from first principles John Levine
- Re: [Asrg] E-postage from first principles Jonathan Morton
- Re: [Asrg] E-postage from first principles John Levine
- Re: [Asrg] E-postage from first principles Jonathan Morton
- [Asrg] Re: Consent protocols - was E-postage John Levine
- [Asrg] Consent protocols - was E-postage David Maxwell
- [Asrg] Re: Consent protocols - was E-postage David Maxwell
- Re: [Asrg] (no subject) Barry Shein
- Re: [Asrg] E-postage from first principles Barry Shein
- Re: [Asrg] E-postage from first principles Yakov Shafranovich
- [Asrg] Re: Consent protocols - was E-postage John Levine
- Re: [Asrg] (no subject) Roger B.A. Klorese
- [Asrg] Re: Consent protocols - was E-postage John Levine
- [Asrg] Re: Consent protocols - was E-postage David Maxwell
- Re: [Asrg] (no subject) Barry Shein
- Re: [Asrg] (no subject) "Roger B.A. Klorese"
- Re: [Asrg] 3 (Message Verification) - Viability o… Jonathan Morton
- [Asrg] Re: Consent protocols - was E-postage David Maxwell
- [Asrg] (no subject) Paul Lambert