[LIPS] Use SHA3-256 hash of transaction header as transactionID

Andreas Kendziorra andreas.kendziorra at lightcurve.io
Fri Feb 1 09:25:51 EST 2019


Dear community,


With this email, I would like to kickoff the discussion for a LIP 
regarding the roadmap objective “Replace transaction ID system”.


The IDs for transactions in Lisk, namely transactionIDs, should be 
computed in a way such that collisions have a negligible probability. 
Although a collision does not pose a security risk, it is inconvenient 
as it corrupts their intended usage: being a unique identifier for a 
transaction.


The length of the currently used transactionIDs, 64 bits, does not 
provide a negligible probability considering the potential number of 
transactions that could get included in the Lisk blockchain in the next 
years. The expected value for the number of transactions after which 
there is a collision of transactionIDs is ~2^32. The proposed change 
regarding the block size (LIP 0002 
<https://github.com/LiskHQ/lips/blob/master/proposals/lip-0002.md>) will 
allow up to 128 transactions per block (assuming the current size of 
transaction objects). If every block contains 128 transactions, a 
collision is expected after approximately 11 years. Hence, 64 bits is 
obviously too short.


We propose to use a length of 256 bits. Assuming that each block 
contains 128 transaction, the probability of having a collision within 
the next 50 years is below 10^(-56). Moreover, we propose to use 
SHA3-256 as the hash function in order to use the same hash function 
family as proposed for the blockIDs and the network identifier (see LIP 
0009 <https://github.com/LiskHQ/lips/blob/master/proposals/lip-0009.md>).


I’m looking forward to your responses and feedback.


Andreas

-- 
Andreas Kendziorra
Cryptographer, Lightcurve
andreas.kendziorra at lightcurve.io
www.lightcurve.io

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