I see lots of posts about witholding salary information on this sub, but I think it mostly doesn’t actually matter.
Don't ask them what they want to pay. Always tell them what you want to be paid. You will either be able to negotiate your salary or quickly expose them for wasting your time.
Negotiation requires you to get into the other persons head.
It’s in your interest to open the negotiation first. Put your demand on the table and pitch a very high number just on the edge of plausible. It’s called 'open extreme'. They will instantly dismiss it, but it’s your offer in their head. They will probably make a miserable counter offer, which you should also instantly dismiss, but you reply with a more plausible offer still in the aggressive high range.
Every time you make a new offer, make your concessions smaller than the previous offer and plan your counter offers, so that you never go lower than the level you're happy with.
When you ask them to open first (i.e. what’s the salary?) you are already making a mistake. The number they give, is their offer in your head and it will be their version of open extreme. You are now thinking about their crappy offer and considering how much more they might consider accepting. The key here, is that you always want them to be considering YOUR offer, never the other way around. Pull them closer to you, do not let them pull you closer to them.
This is why you should not care, if a company won't tell you what their salary range is. All you achieve otherwise, is to restrict how successful you can be in your negotiation since you are giving credibility to their artifical limits.
One of the reasons employers don’t publish salaries, is that they want to first try to understand what your “breakpoint” is. They want to know at what offer value, will mean the candidate will simply walk away. Once they think they understand this, then they give an offer which is either at or just below that threshold, (assuming they want to hire you of course). Information is KING. They want to open extreme, but must not be so extreme as to scare you off at the outset, so the shittier companies use the recruitment process to understand what your break point is.
So don’t tell them what your current/old salary or anything at all to give them an upper hand in the negotiation, instead give them an open extreme offer. Planning is critical, try to predict their break point and plan your offers with diminishing concessions. Remember.. Open Extreme.. keep making offers, and keep your offer in their head.
(I have recently completed a 10 day course in negotiation training as part of my job).
Good Luck!