One thing I have pointed out in the past (and likely will need to continue to point out for a very long time ) is that DWAVE's system implements (or it stated to implement there is some controversy over exact what is happening) quantum annealing algorithm which while it does (or may) have some quantum properties is not the same thing as a general purpose quantum computer.

To attack public encryption requires a general purpose quantum computer (QPQC) capable of implementing Shor's algorithm (or one built to only implement ONLY Shor's algorithm, a quantum "ASIC" if you will).  Even if DWAVE's computer was a quadrillion qubits it would be absolutely useless for attacking public encryption.  

The global recognition for successfully factoring larger numbers using a GPQC and Shor's algorithm is a pretty big deal.  To date nobody publicly has shown the ability to factor numbers larger than 143 (an 8 bit number).  Even factoring 32 bit numbers at commercially viable speeds would probably mean we are decades away from being able to break 256 bit ECC keys but we aren't even close to that.  While QC is powerful in theory, practical progress has also been agonizingly slow:

2001
First successful demonstration of Shor's algorithm.
Computer size:  7 qubits
Number factored: 15 (into the factors 5 & 3)
Equivelent RSA keysize: 4 bit

2011
First successful factorization of a three digit number (143)
Computer size:  8 qubits (actually 4 bits using an iterative process)
Number factored: 143 (into the factors 11 & 13)
Equivelent RSA keysize: 8 bit

So the bit strength of "encryption" (I use this term loosely because one could crack 8 bit "encryption" with paper and pencil) that can be broken using QC has gone from 4 bit to 8 bit after a decade of research.  Even if this can scale, at the current growth rate breaking Bitcoin would be more than a lifetime away.  ECDSA is a little different than RSA in that it doesn't involve factoring large numbers and instead uses the properties of elliptical curves but both can be broken using Shor's algorithm.  In general ECC requires smaller keys than RSA for an equivelent level of security.  To achieve 128 bit key strength (which is considered beyond brute force for classical computing) using ECDSA requires 256 bits, but using RSA requires 3,072 bits. Bitcoin could use RSA and be just as secure however transactions would be up 12x as large.  

Still both RSA and ECC in theory can be broken faster than what is possible with classical computing by using a large enough (and fast enough) quantum computer implementing Shor's algorithm. I have only found one paper to date which compares the qubit cost of implementing Shor's algorithm against both RSA & ECC.

http://arxiv.org/pdf/quantph/0301141.pdf  I emphasis of relevant portions is by me.  

So we are looking at a general purpose quantum computer which needs at least 1,800 logical qubits.  Nobody (AFAIK) has even done research on the amount of error correction required for a commercial general purpose quantum computer (because none exists) but lets take the authors estimate of "dozens of physical qubits per logical qubit" and use 24x as a low end.   This would mean (1,800 * 24) a system with 43,200 or more physical qubits.  To put that into perspective the largest (AFAIK please correct me if you find a larger example) general purpose quantum computer capable of implementing Shor's algorithm is ... 7 qubits so we aren't eve in striking range yet.

Still QC "may" may break 256 bit ECDSA within our lifetime, so should be looking to future solutions.  There are a couple things which can be done to improve the quantum security of the Bitcoin network.  The simplest change would be to implement a new address type which uses a larger ECC curve.  While larger ECDSA keys can sitll be broken they do increase the qubit requirements, moving to 512 bit keys doubles the required qubits and 1,024 will quadruple them.  If GPQC proves viable this would buy the network some time for a longer term solution.  I don't even know if 1,024 bit ECC is supported by major libraries, outside of quantum computing there is little need for 1,024 bit ECC because even 256 bit ECC is considered beyond brute force. 

A longer term and more complex solution would be moving to an address scheme based on a post-quantum algorithms (http://en.wikipedia.org/wiki/Post-quantum_cryptography).  These systems generally have no wide spread deployment so there may be unknown security issues so I am not advocating a change anytime soon just pointing out there are algorithms which can be used to protect the network even if large GPQC become available.   The largest obstacle to these post quantum systems is generally they involve much much larger public keys.  The bandwidth and storage requirements of Bitcoin are highly correlated to the size of the public key and we are talking about public keys in the tens of kilobytes (notice the plural) so transactions and blocks would be easily a hundred times larger.   Now it is entirely possible that Moore's law will mitigate this somewhat,  and stat using a 50,000 byte key in 2048 will be no more of a challenge then using a 256 bit key today.

For those who are interested in post quantum cryptography one implementation (which has open source implementation) is NTRU.  It is likely far too early to consider any such implementation in a production system but implementing a patched version of bitcoin on testnet which incorporates NTRU would be an interesting project.

To summarize, the OP is wrong. Bitcoin is not doomed because 256 bit keys are beyond brute force using anything that can be manufactured and we could always fork Bitcoin to 512 which is beyond beyond brute force but that will create a blockchain requiring a hard drive the size of Chevy van. lol

Whow, he makes Iranian nuclear bombs look like the last straw of hope for the human race

Seems like the appropriate thread for this:

http://www.eetimes.com/document.asp?doc_id=1326468&_mc=NL_EET_EDT_EET_daily_20150429&cid=NL_EET_EDT_EET_daily_20150429&elq=a59559bfb7664cde842c7b2bb9e68b8c&elqCampaignId=22769&elqaid=25618&elqat=1&elqTrackId=6252292228f14224804cfbfa4bed4c75

I like how you stopped posting at 666.

"There is as yet insufficient data for a meaningful answer."

Nice article.
I think the Skynet robots will keep using Bitoins after they have destroyed the human race, because they will think it's perfect. I don't see any problem for Bitcoin here. Chill.

for those who are too busy/lazy to read D&T's statement, my interpretation is:

If QC starts to look like a threat to Bitcoin over the coming decades, a hardfork could be done into a new set of software and blockchain, that is QC proof. Basically a migration.

The only thing is that this migration has to be done early enough to prevent an (QC proof) altcoin from taking over. 

This is basically a science fiction entertainment for those that have too much free time. No, SHA256 is still safe, and if it cracked, the banking system would collapse as well since everything is running under SHA256 those days, from ATMs to electronic payment systems that each bank has implemented for their internet transactions, Paypal would get hit hard as well.