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From: Gavin Andresen <gavinandresen@gmail.com>
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Subject: [Bitcoin-development] Pull request: faster initial blockchain
	download
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I'd appreciate review/feedback on this:

https://github.com/bitcoin/bitcoin/pull/492

This change skips ECDSA signature verification for transactions during
the initial block-chain download, which makes downloading the block
chain much faster.

"Initial block chain download" is all blocks up to 120 blocks before
the last blockchain lock-in point.

Reasoning for why this is safe:

If an attacker tries to feed a client bad transactions during the
initial block-chain download (transactions with invalid signatures),
then they change the merkle tree, and at the first blockchain lock-in
the bad chain will be rejected.

Transactions are still checked for orphan blocks that come in during
initial block-chain-download (ConnectInputs will be called with
fBlock=FALSE) and for mined blocks (ConnectInputs called with
fMiner=TRUE).

-- 
--
Gavin Andresen