[Bitcoin-development] Synchronization: 19.5 % orphaned blocks at height 197'324

[Bitcoin-development] Synchronization: 19.5 % orphaned blocks at height 197'324

[mbde]

Hello all,

I'm currently synchronizing a new node and right now, at a progress of a
height of 197'324 blocks, I count in my debug.log an aweful amount of
38'447 orphaned blocks which is about 19.5 %.

It has been I while since I watched the synchronization process closely,
but this number seems pretty high to me.

I'm wondering about the following: would it be possible for a malicious
party to generate chains of blocks with low difficulity which are not
part of the main chain to slow down the sync process?


Build and version information:
https://github.com/jmcorgan/bitcoin/tree/026686c7de76dfde6fcacfc3d667fb3418a946a7
(sipa/jmcorgan address index)
Rebased with:
https://github.com/bitcoin/bitcoin/tree/94e1b9e05b96e4fe639e5b07b7a53ea216170962
(almost up-to-date mainline)

Compressed debug.log attached:
https://www.dropbox.com/s/uvtd91xiwmdmun7/debug.7z?m=
(filesize: 7.67 MB, uncompressed: 41.3 MB)

Re: [Bitcoin-development] Synchronization: 19.5 % orphaned blocks at height 197'324

[Bob McElrath]

[-- Attachment #1.1: Type: text/plain, Size: 2046 bytes --]

I had the same problem (repeatedly) which came down a hardware problem.  Bitcoin
more than other applications is very sensitive to single bit flips in memory or
during computation.  (In the end I under-clocked my CPU and RAM to fix the
problem)

Attached is a small python script which will run sha256 on random data
repeatedly and will print a message if a mismatch is found.  For me it took many
hours of running before a sha256 mismatch, but one is enough to fork the
blockchain.

mbde@bitwatch.co [mbde@bitwatch.co] wrote:
> Hello all,
> 
> I'm currently synchronizing a new node and right now, at a progress of a
> height of 197'324 blocks, I count in my debug.log an aweful amount of
> 38'447 orphaned blocks which is about 19.5 %.
> 
> It has been I while since I watched the synchronization process closely,
> but this number seems pretty high to me.
> 
> I'm wondering about the following: would it be possible for a malicious
> party to generate chains of blocks with low difficulity which are not
> part of the main chain to slow down the sync process?
> 
> 
> Build and version information:
> https://github.com/jmcorgan/bitcoin/tree/026686c7de76dfde6fcacfc3d667fb3418a946a7
> (sipa/jmcorgan address index)
> Rebased with:
> https://github.com/bitcoin/bitcoin/tree/94e1b9e05b96e4fe639e5b07b7a53ea216170962
> (almost up-to-date mainline)
> 
> Compressed debug.log attached:
> https://www.dropbox.com/s/uvtd91xiwmdmun7/debug.7z?m=
> (filesize: 7.67 MB, uncompressed: 41.3 MB)
> 
> ------------------------------------------------------------------------------
> _______________________________________________
> Bitcoin-development mailing list
> Bitcoin-development@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/bitcoin-development
--
Cheers, Bob McElrath

"The individual has always had to struggle to keep from being overwhelmed by
the tribe.  If you try it, you will be lonely often, and sometimes frightened.
But no price is too high to pay for the privilege of owning yourself." 
    -- Friedrich Nietzsche

[-- Attachment #1.2: sha256check.py --]
[-- Type: text/x-python, Size: 792 bytes --]

#!/usr/bin/python

# Repeatedly run a sha256 on random data.  Keeps a rolling buffer of the last
# <buflen> hashes and re-checks them.  Prints an error ONLY if a mismatch is
# found.  If a mismatch is found, you have a hardware problem.

from hashlib import sha256
from collections import deque
import random

buflen = 100000
hashbuf = deque(maxlen=buflen)

for i in range(buflen):
    hashbuf.append([str(i), sha256(str(i)).hexdigest()])

while True:
    k, khash = hashbuf.popleft()
    pophash = sha256(k).hexdigest()
    if pophash != khash:
        print "ERROR: sha256(%s) = %s does not match:"%(k, khash)
        print "       sha256(%s) = %s"%(k, pophash)
    k = str(random.getrandbits(1000))
    khash = sha256(k).hexdigest()
    hashbuf.append([k, khash])

[-- Attachment #2: Digital signature --]
[-- Type: application/pgp-signature, Size: 198 bytes --]

Re: [Bitcoin-development] Synchronization: 19.5 % orphaned blocks at height 197'324

[Pieter Wuille]

On Sun, Aug 10, 2014 at 4:07 PM, Bob McElrath <bob_bitcoin@mcelrath.org> wrote:
> I had the same problem (repeatedly) which came down a hardware problem.

This is actually an independent problem (though something to be aware
of). Flaky hardware can make synchronization fail completely - as it
relies on being able to exactly assess the validity of everything in
the blockchain.

Stilll...

> mbde@bitwatch.co [mbde@bitwatch.co] wrote:
>> Hello all,
>>
>> I'm currently synchronizing a new node and right now, at a progress of a
>> height of 197'324 blocks, I count in my debug.log an aweful amount of
>> 38'447 orphaned blocks which is about 19.5 %.
>>
>> It has been I while since I watched the synchronization process closely,
>> but this number seems pretty high to me.

Orphan blocks during synchronization are unfortunately very common,
and the result of a mostly broken download logic in the client. They
are blocks that are further ahead in the chain than the point where
you're currently synchronized to, and thus can't be validated yet.
Note that 'orphan' here means 'we do not know the parent'; it doesn't
just mean 'not in the main chain'. They are blocks that are received
out of order.

As Jeff mentions, headers-first synchronization fixes this problem
(and many other download-logic related things), by first verifying the
headers in the chain (thus already having partially validated
everything), and then downloading the blocks (in not necessarily the
right order) anymore, from multiple peers in parallel. There is
currently a pull request for it, but it's not production ready
(#4468).

>> I'm wondering about the following: would it be possible for a malicious
>> party to generate chains of blocks with low difficulity which are not
>> part of the main chain to slow down the sync process?

Yes and no. While you're still synchronization, and don't actually
know the best chain, a peer could send you stale branches (with valid
proof of work), which you would accept, store and process. But it has
to be done very early, as once you learn of a good-enough chain, a
branch with more proof of work would be requires due to some
heuristics designed to exactly prevent such an attack.

-- 
Pieter

Re: [Bitcoin-development] Synchronization: 19.5 % orphaned blocks at height 197'324

[Jeff Garzik]

This issue is being worked on, under the category of "headers first
synchronization."

Until that is finished, it is recommended that you download
bootstrap.dat via torrent:
https://bitcointalk.org/index.php?topic=145386.0


On Sun, Aug 10, 2014 at 9:42 AM, mbde@bitwatch.co <mbde@bitwatch.co> wrote:
> Hello all,
>
> I'm currently synchronizing a new node and right now, at a progress of a
> height of 197'324 blocks, I count in my debug.log an aweful amount of
> 38'447 orphaned blocks which is about 19.5 %.
>
> It has been I while since I watched the synchronization process closely,
> but this number seems pretty high to me.
>
> I'm wondering about the following: would it be possible for a malicious
> party to generate chains of blocks with low difficulity which are not
> part of the main chain to slow down the sync process?
>
>
> Build and version information:
> https://github.com/jmcorgan/bitcoin/tree/026686c7de76dfde6fcacfc3d667fb3418a946a7
> (sipa/jmcorgan address index)
> Rebased with:
> https://github.com/bitcoin/bitcoin/tree/94e1b9e05b96e4fe639e5b07b7a53ea216170962
> (almost up-to-date mainline)
>
> Compressed debug.log attached:
> https://www.dropbox.com/s/uvtd91xiwmdmun7/debug.7z?m=
> (filesize: 7.67 MB, uncompressed: 41.3 MB)
>
> ------------------------------------------------------------------------------
> _______________________________________________
> Bitcoin-development mailing list
> Bitcoin-development@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/bitcoin-development



-- 
Jeff Garzik
Bitcoin core developer and open source evangelist
BitPay, Inc.      https://bitpay.com/