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Project Euler Returns

projecteuler.net

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Re: Project Euler Returns

#101

Post by e12e »

lunixbochs wrote: post #100
e12e wrote: post #61

Earlier quoted context omitted.

> To be fair, your bank likely has a bit more money to throw at this problem. I suppose they could charge 1 USD for (lifetime) membership and store the last four digits of your credit card in lieu of a username, so that they could easily look up the salt that gives the salt with witch they've hashed your email... ;-) (Would require that you could supply the last digits of your possibly expired credit card, when you l…

The last four digits of your credit card should not be considered secure information. It's printed on all of your receipts. You carry it on your person in plain text. Many of your online accounts will display it in your account settings without an additional login. It's probably in both your mail and your email. Once someone has it, they can use it for years for recovery on any service that accepts it, and I know som…

True enough. On the other hand, all this is to avoid storing a username, which also isn't secure information.

Re: Project Euler Returns

#102

Post by runamok »

stouset wrote: post #83
owenversteeg wrote: post #79

Earlier quoted context omitted.

A global salt is called 'pepper'.

This thread is dishearteningly full of cargo-culted cryptography. You would think HN would do better. A global salt is not a thing. It's a misapplication of a cryptographic component. The appropriate tool when you think you need something like this is an HMAC and a secret HMAC key.

Once again we are talking about having an email retrieval function while not storing the email address in plaintext. A "global salt" or "pepper" (as we are apparently calling it now) just prevents enormous pre-generated rainbow tables but admittedly in today's gpu dominated cracking environment it probably doesn't get you much.

Personally I think not having a password retrieval function while simultaneously forcing all of your users to reset their password is a pretty user unfriendly tactic for the protection of an ostensibly public piece of information.

Re: Project Euler Returns

#104

Post by ghusbands »

neutronicus wrote: post #54
Bootvis wrote: post #3

I have been curious for a while: What is in the opinion of the HN community a good score on Project Euler? For which scores do you tip your figurative hat?

Not scores so much as specific problems. If I work on it for a week, get frustrated, google for solutions, and can't find any, and you solved it, you're a beast. Also if you solve 328 tell me how. And no, dynamic programming is not efficient enough.

It's easier than you might think. Only read this comment as far as you need to make a little more progress. These hints only apply if you're starting with a dynamic programming approach. Also, they're only helpful if you do the work, so I don't think they violate the spirit of Project Euler.

Is your dynamic programming table 2D? Maybe it should be.

Stop reading if that's progress.

Have you looked closely at the table content?

Stop reading.

Have you noticed how similar many parts are, under perhaps simple transforms?

Stop reading.

Try adding or subtracting your coordinates, to see more of the pattern.

Stop reading.

There's not just a within-row pattern.

Stop reading.

In the end, dynamic programming might not be the main trick. But you can make your own way from here.

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