DarkSend is immune to such attacks, all involved crypto functions could be cracked and the mixing is still done off blockchain by the masternodes. Off blockchain means that the information is lost and that's the only way to secure it, you can't do it with cryptography.
See if I haven't been banging on about the advantages of a 2-tier network for weeks now.
- legacy compliance with Bitcoin commercial infrastructure
- decoupled scope of anon-tech allowing for evolutionary or revolutionary revisions to be firewalled off from the blockchain development
- ability to support pre-emtive rather than reactive anonymisation
- ability to support multiple redundancy anonymisation as opposed to just single redundancy with single-tier network
- following on from that, massive resistance against attacks on algo weaknesses due to multiple redundancy mixing
and now (now being back in April 2014 but I just saw it 'now') Evan has added...
- resistance to cracking by shor's algorithm