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