From: Tamas Blummer <tamas@bitsofproof•com>
To: Wladimir <laanwj@gmail•com>
Cc: Bitcoin Dev <bitcoin-development@lists•sourceforge.net>
Subject: Re: [Bitcoin-development] var_int ambiguous serialization consequences
Date: Sun, 1 Feb 2015 12:42:05 +0100 [thread overview]
Message-ID: <B2C9D852-1C58-4F33-B17E-2E6A377E3B70@bitsofproof.com> (raw)
In-Reply-To: <alpine.DEB.2.10.1502011133510.21504@nzrgulfg.ivfhpber.pbz>
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Thanks for the clarification. Yes, I referred to CompactSize using the lingo of https://en.bitcoin.it/wiki/Protocol_documentation
I am not sure if it is current concern. Apparently an exception is thrown if non-canonical CompactSize in a transaction s parsed.
Is it ensured that transactions are always parsed before computing their hash?
Tamas Blummer
On Feb 1, 2015, at 11:44 AM, Wladimir <laanwj@gmail•com> wrote:
>
> On Sun, 1 Feb 2015, Tamas Blummer wrote:
>
>> I wonder of consequences if var_int is used in its longer than necessary forms (e.g encoding 1 as 0xfd0100 instead of 0x01)
>
> In serialize.h lingo you are talking about CompactSize, not VarInt.
>
> CompactSizes indeed have redundancy in their representation, i.e. the same number can be represented as up to four different byte sequences.
>
> VARINTs have a different format that (AFAIK) isn't used anywhere in the block chain. See WriteVarInt / ReadVarInt. These were designed to not have any redundancy in their representation.
>
>> This is already of interest if applying size limit to a block, since transaction count is var_int but is not part of the hashed header or the
>> merkle tree.
>
> Are you sure that this is a current concern? Non-canonical CompactSizes are forbidden - in serialize.h this is flagged in ReadCompactSize.
>
> Wladimir
>
>
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next prev parent reply other threads:[~2015-02-01 11:42 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-02-01 9:33 Tamas Blummer
2015-02-01 10:44 ` Wladimir
2015-02-01 11:42 ` Tamas Blummer [this message]
2015-02-01 15:00 ` Pieter Wuille
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