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From: Tier Nolan <tier.nolan@gmail.com>
Cc: Bitcoin Dev <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] Time to worry about 80-bit collision attacks or not?
Date: Mon, 11 Jan 2016 23:57:59 +0000	[thread overview]
Message-ID: <CAE-z3OUMRivWPVA+3BgC_95MGYBHN34+hoo6xfCu_gNeLFVknA@mail.gmail.com> (raw)
In-Reply-To: <CABsx9T3MfndREm9icE-TUF58zsRZ5YsBMvUAMy4E-MmYWxWV=A@mail.gmail.com>

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On Fri, Jan 8, 2016 at 3:46 PM, Gavin Andresen via bitcoin-dev <
bitcoin-dev@lists.linuxfoundation.org> wrote:

> How many years until we think a 2^84 attack where the work is an ECDSA
> private->public key derivation will take a reasonable amount of time?
>

I think the EC multiply is not actually required.  With compressed public
keys, the script selection rule can just be a sha256 call instead.

V is the public key of the victim, and const_pub_key is the attacker's
public key.

     if prev_hash % 2 == 0:
        script = "2 V 0x02%s 2 CHECKMULTISIG" % (sha256(prev_hash)))
    else:
        script = "CHECKSIG %s OP_DROP" % (prev_hash, const_pub_key)

    next_hash = ripemd160(sha256(script))

If a collision is found, there is a 50% chance that the two scripts have
different parity and there is a 50% chance that a compressed key is a valid
key.

This means that you need to run the algorithm 4 times instead of 2.

The advantage is that each step is 2 sha256 calls and a ripemd160 call.  No
EC multiply is required.

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  parent reply	other threads:[~2016-01-11 23:58 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-01-07 19:02 [bitcoin-dev] Time to worry about 80-bit collision attacks or not? Gavin Andresen
2016-01-07 19:13 ` Matt Corallo
2016-01-07 19:19 ` Adam Back
2016-01-07 20:56   ` Dave Scotese
2016-01-07 21:06     ` Gavin Andresen
2016-01-07 22:56       ` Ethan Heilman
2016-01-07 23:39         ` Gavin Andresen
2016-01-08  1:26           ` Matt Corallo
2016-01-08  1:54             ` Gavin Andresen
2016-01-08 17:38               ` Pieter Wuille
2016-01-08 18:41               ` Peter Todd
2016-01-07 20:40 ` Ethan Heilman
2016-01-07 23:52 ` Pieter Wuille
2016-01-08  1:00   ` Gavin Andresen
2016-01-08  1:27     ` Watson Ladd
2016-01-08  3:30   ` Rusty Russell
2016-01-08  3:41     ` Matt Corallo
2016-01-08 12:02       ` Rusty Russell
2016-01-08 12:38         ` Gavin Andresen
2016-01-08 14:34           ` Watson Ladd
2016-01-08 15:26             ` Adam Back
2016-01-08 15:33           ` Anthony Towns
2016-01-08 15:46             ` Gavin Andresen
2016-01-08 15:50               ` Gavin Andresen
2016-01-08 15:59                 ` Gavin Andresen
2016-01-11 20:32                 ` Jorge Timón
2016-01-08 16:06               ` Gavin Andresen
2016-01-11  3:57               ` Rusty Russell
2016-01-11  6:57                 ` Peter Todd
2016-01-11 23:57               ` Tier Nolan [this message]
2016-01-12  0:00                 ` Tier Nolan
2016-01-12 12:08                   ` Gavin Andresen
2016-01-12 23:22                     ` Zooko Wilcox-O'Hearn
2016-01-08 18:52     ` Peter Todd

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