user9382: The recent re-emergence of transaction malleability has been responsible for a large number of Txs which are being double spent (October 2015).
/r/Bitcoin has posted some C++ code which @amaclin has taken responsibility for. 
I understand that, based on this source code, the transaction malleability "exploit" is simply tweaking the DER signatures for certain Txs (ie non P2SH Txs) and rebroadcasting the Tx (disclaimer: I don't know C++ so these are educated guesses). 
BIP62 deals with numerous issues, amongst these is the requirement for canonical DER signatures: I was under the impression canonical DER signatures was implemented in BIP66. 

Can someone clarify what @amaclin's code is doing?
Why is this exploit possible if BIP66 was implemented several weeks ago?


user7267: Canonical DER signature implemented in BIP 66 fixes issue #1 of BIP 62 ( Non-DER encoded ECDSA signatures ) 
Amacilin's code exploits issue #5 in BIP 62 ( Inherent ECSDA signature malleability ),  and is explained here : https://github.com/bitcoin/bitcoin/commit/a81cd96805ce6b65cca3a40ebbd3b2eb428abb7b 
This issue was fixed by requiring signatures to have low-S encoding in pull request 6769 : https://github.com/bitcoin/bitcoin/pull/6769 . Note that this fix only prevents mutated transactions from being relayed (transactions without low-S encoding can still be mined into blocks).

9382: <p>The recent re-emergence of transaction malleability has been responsible for a large number of Txs which are being double spent (October 2015).</p>

<p><a href="https://www.reddit.com/r/Buttcoin/comments/3okxo5/does_amaclin_need_some_btc_to_wreck_havoc/cvyfy53">/r/Bitcoin has posted</a> some C++ code which @amaclin has taken responsibility for. </p>

<p>I understand that, based on this source code, the transaction malleability "exploit" is simply tweaking the DER signatures for certain Txs (ie non P2SH Txs) and rebroadcasting the Tx (<em>disclaimer: I don't know C++ so these are educated guesses</em>). </p>

<p>BIP62 deals with numerous issues, amongst these is the requirement for canonical DER signatures: I was under the impression canonical DER signatures was implemented in BIP66. </p>

<ol>
<li>Can someone clarify what @amaclin's code is doing?</li>
<li>Why is this exploit possible if BIP66 was implemented several weeks ago?</li>
</ol>
 7267: <p>Canonical DER signature implemented in BIP 66 fixes issue #1 of BIP 62 ( Non-DER encoded ECDSA signatures ) </p>

<p>Amacilin's code exploits issue #5 in BIP 62 ( Inherent ECSDA signature malleability ),  and is explained here : <a href="https://github.com/bitcoin/bitcoin/commit/a81cd96805ce6b65cca3a40ebbd3b2eb428abb7b">https://github.com/bitcoin/bitcoin/commit/a81cd96805ce6b65cca3a40ebbd3b2eb428abb7b</a> </p>

<p>This issue was fixed by requiring signatures to have low-S encoding in pull request 6769 : <a href="https://github.com/bitcoin/bitcoin/pull/6769">https://github.com/bitcoin/bitcoin/pull/6769</a> . Note that this fix only prevents mutated transactions from being relayed (transactions without low-S encoding can still be mined into blocks).</p>
