From: Ethan Heilman <eth3rs@gmail•com>
To: Rusty Russell <rusty@rustcorp•com.au>,
Bitcoin Protocol Discussion
<bitcoin-dev@lists•linuxfoundation.org>
Subject: Re: [bitcoin-dev] BIP 151 use of HMAC_SHA512
Date: Tue, 28 Jun 2016 21:56:55 -0400 [thread overview]
Message-ID: <CAEM=y+XKQZVz6UieB-nDy_C9xTmXiBB3-atuuZkxzmPoSVPOJw@mail.gmail.com> (raw)
In-Reply-To: <8760ssdd1u.fsf@rustcorp.com.au>
>It's also not clear to me why the HMAC, vs just SHA256(key|cipher-type|mesg). But that's probably just my crypto ignorance...
SHA256(key|cipher-type|mesg) is an extremely insecure MAC because of
the length extension property of SHA256.
If I have a tag y = SHA256(key|cipher-type|mesg), I can without
knowing key or msg compute a value y' such that
y' = SHA256(key|cipher-type|mesg|any values I want).
Thus, an attacker can trivially forge a tag protected by
SHA256(key|cipher-type|mesg).
For more details see:
https://web.archive.org/web/20141029080820/http://vudang.com/2012/03/md5-length-extension-attack/
On Tue, Jun 28, 2016 at 9:00 PM, Rusty Russell via bitcoin-dev
<bitcoin-dev@lists•linuxfoundation.org> wrote:
> Jonas Schnelli <dev@jonasschnelli•ch> writes:
>>> To quote:
>>>
>>>> HMAC_SHA512(key=ecdh_secret|cipher-type,msg="encryption key").
>>>>
>>>> K_1 must be the left 32bytes of the HMAC_SHA512 hash.
>>>> K_2 must be the right 32bytes of the HMAC_SHA512 hash.
>>>
>>> This seems a weak reason to introduce SHA512 to the mix. Can we just
>>> make:
>>>
>>> K_1 = HMAC_SHA256(key=ecdh_secret|cipher-type,msg="header encryption key")
>>> K_2 = HMAC_SHA256(key=ecdh_secret|cipher-type,msg="body encryption key")
>>
>> SHA512_HMAC is used by BIP32 [1] and I guess most clients will somehow
>> make use of bip32 features. I though a single SHA512_HMAC operation is
>> cheaper and simpler then two SHA256_HMAC.
>
> Good point; I would argue that mistake has already been made. But I was
> looking at appropriating your work for lightning inter-node comms, and
> adding another hash algo seemed unnecessarily painful.
>
>> AFAIK, sha256_hmac is also not used by the current p2p & consensus layer.
>> Bitcoin-Core uses it for HTTP RPC auth and Tor control.
>
> It's also not clear to me why the HMAC, vs just
> SHA256(key|cipher-type|mesg). But that's probably just my crypto
> ignorance...
>
> Thanks!
> Rusty.
> _______________________________________________
> bitcoin-dev mailing list
> bitcoin-dev@lists•linuxfoundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
next prev parent reply other threads:[~2016-06-29 1:57 UTC|newest]
Thread overview: 59+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-28 2:31 Rusty Russell
2016-06-28 7:17 ` [bitcoin-dev] BIP 151 Eric Voskuil
2016-06-28 8:26 ` Jonas Schnelli
2016-06-28 16:45 ` Eric Voskuil
2016-06-28 18:22 ` Peter Todd
2016-06-28 18:35 ` Eric Voskuil
2016-06-28 20:14 ` Peter Todd
2016-06-28 20:29 ` Eric Voskuil
2016-06-28 20:36 ` Peter Todd
2016-06-28 21:22 ` Eric Voskuil
2016-06-28 21:36 ` Gregory Maxwell
2016-06-28 21:40 ` Cameron Garnham
2016-06-28 22:07 ` Eric Voskuil
2016-06-28 22:33 ` Cameron Garnham
2016-06-28 23:29 ` Eric Voskuil
2016-06-29 0:06 ` Nick ODell
2016-06-28 21:59 ` Eric Voskuil
[not found] ` <CAAS2fgQ0Ocs8hF+pf+fWfkKKhQwxNKpY=JHpb_bwua7neVO8tg@mail.gmail.com>
2016-06-28 23:34 ` Eric Voskuil
2016-06-28 20:06 ` Jonas Schnelli
2016-06-28 23:31 ` Eric Voskuil
2016-06-29 11:17 ` Alfie John
2016-06-30 11:56 ` Eric Voskuil
2016-06-30 12:20 ` Jonas Schnelli
2016-06-30 12:27 ` Eric Voskuil
2016-06-30 12:43 ` Jonas Schnelli
2016-06-30 15:22 ` Eric Voskuil
2016-06-30 16:52 ` Peter Todd
2016-06-30 18:25 ` Eric Voskuil
2016-06-30 19:06 ` Peter Todd
2016-06-30 20:26 ` Eric Voskuil
2016-06-28 19:55 ` Gregory Maxwell
2016-06-28 23:33 ` Eric Voskuil
2016-06-29 1:01 ` Gregory Maxwell
2016-06-30 9:57 ` Eric Voskuil
2016-06-30 13:03 ` Pieter Wuille
2016-06-30 15:10 ` Eric Voskuil
2016-08-31 14:29 ` Pieter Wuille
2016-06-30 13:36 ` Erik Aronesty
2016-06-30 14:47 ` Alfie John
2016-07-02 9:44 ` Chris Priest
2016-06-28 12:13 ` Jonas Schnelli
2016-06-28 17:39 ` Eric Voskuil
2016-06-28 7:19 ` [bitcoin-dev] BIP 151 use of HMAC_SHA512 Jonas Schnelli
2016-06-28 8:31 ` Arthur Chen
2016-06-29 18:34 ` Jonas Schnelli
2016-06-29 20:13 ` Peter Todd
2016-06-29 20:31 ` Jonas Schnelli
2016-06-29 1:00 ` Rusty Russell
2016-06-29 1:38 ` Arthur Chen
2016-06-29 1:56 ` Ethan Heilman [this message]
2016-06-29 6:58 ` Pieter Wuille
2016-06-29 14:38 ` Ethan Heilman
2016-06-29 18:46 ` Jonas Schnelli
2016-07-01 3:25 ` Rusty Russell
2016-07-01 22:42 ` Zooko Wilcox
2016-07-04 1:23 ` Arthur Chen
2016-07-04 1:44 ` Arthur Chen
2016-07-04 6:47 ` Jonas Schnelli
2016-07-04 6:37 ` Jonas Schnelli
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