public inbox for bitcoindev@googlegroups.com
 help / color / mirror / Atom feed
From: Pieter Wuille <pieter.wuille@gmail.com>
To: Ethan Heilman <eth3rs@gmail.com>,
	Bitcoin Dev <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] BIP 151 use of HMAC_SHA512
Date: Wed, 29 Jun 2016 08:58:21 +0200	[thread overview]
Message-ID: <CAPg+sBj3QRGYUzJn96ZS4bf1ZEH9KTwF+OxPXE-O_YJA66grBg@mail.gmail.com> (raw)
In-Reply-To: <CAEM=y+XKQZVz6UieB-nDy_C9xTmXiBB3-atuuZkxzmPoSVPOJw@mail.gmail.com>

[-- Attachment #1: Type: text/plain, Size: 829 bytes --]

On Jun 29, 2016 07:05, "Ethan Heilman via bitcoin-dev" <
bitcoin-dev@lists.linuxfoundation.org> wrote:
>
> >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.

This property does technically not apply here, as the output of the hash is
kept secret, and the possible messages are constants (which are presumably
chosen in such a way that one is never an extension of another).

However, this is a good example of why you can't generically use a hash
function in places where you want a MAC (aka "a hash with a shared
secret"). Furthermore, if you already have a hash function anyway, HMAC is
very easy construct on top of it.

-- 
Pieter

[-- Attachment #2: Type: text/html, Size: 1049 bytes --]

  reply	other threads:[~2016-06-29  6:58 UTC|newest]

Thread overview: 59+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-06-28  2:31 [bitcoin-dev] BIP 151 use of HMAC_SHA512 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
2016-06-29  6:58       ` Pieter Wuille [this message]
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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=CAPg+sBj3QRGYUzJn96ZS4bf1ZEH9KTwF+OxPXE-O_YJA66grBg@mail.gmail.com \
    --to=pieter.wuille@gmail.com \
    --cc=bitcoin-dev@lists.linuxfoundation.org \
    --cc=eth3rs@gmail.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox