Kdtyjb

You know this is going to happen and it appears to be important to the culture in your office.

Plan your day so you are doing easily interruptible work (for example, answering emails) at that time.

Don't try to "get in the flow" when you know you will be interrupted

Getting along well with your coworkers is at least as important to your career as writing good code.

You don't need to encourage extended conversation, but it's important that you are thought of as "one of us".

Don't hide.

Easiest option to avoid upsetting others is to find a quiet room for 30 or 40 minutes at the start, and end, of the day so you are just not there when they stream by.

Any other suggestion, such as "pretend a sports injury" etc etc don't work for extended periods...

You could take a comical approach and attach a plastic hand near your desk with a sign for people to shake, they will probably laugh and get the message.

I have been through the same and I understand that social conventions sometimes are inconvenient (or undesired when involving physical contact like birthday hugs).

In my experience, most people will eventually get used to your preferences. I would explain to each one your reasons and politely ask to say hi in a less distracting way, for example, just waving.
Some will be offended but there is nothing wrong with wanting your focus to remain intact while you work and while you respectfully draw limits, there should be no problem.
Also, talking to everyone individually, you can explain without hurting their feelings, you give the message of being important enough to have "the talk", and give them a chance to process it.

I would avoid just not answering the shake from one day to another because they will probably be confused by the behavioural change and will assume the reason ("he's becoming weird", "what did I do?"), and potentially damage your social life there (not receiving after-office activities invitation, eating alone, etc). Leave the least space to assumptions and you should be fine.

Resist the handshake, you should not be forced to give out handshakes as if they were high fives in a 90s teenage TV show. Do as user Jayson said you should do, or start doing your own thing. Point at them and tell them "you're the man" (if applicable). Or start presenting the left hand instead of the right hand. Some people will get the hint, some will just stop coming at your desk, not wanting to be bothered by "Eugene A's latest handshake prank". A few will stick around, and that's when you start having fun with them.

tl;dr: Use pomodoros as a real-life 'busy status' indicator.

Most people do not interrupt out of malice, or even lack of consideration. They do it to be sociable, because they like you and want to interact. As such, stopping them from doing so is probably going to pass a bad message.
On the other hand, given they do it because they like you, if they are made aware from visible cues that their interruption will cause you grief at a particular point you're trying to focus, then they will be more likely to wait until you look less busy next time.

So to an extent, this is also your failure in that you accommodate such interruptions without signifying that they were inappropriately timed.

As a possible solution, I recommend applying the pomodorro technique, both in terms of ensuring your focus, but also as a strong visible social cue that an interruption would be inappropriate. If you're not familiar with it, basically you set a VISIBLE (or even somewhat audible!) timer for 25 minute slots (with 5-minute breaks), during which you're expected to have ABSOLUTE focus on your task. If an interruption occurs, you postpone its action for when the pomodoro period is over, unless it's impossible to avoid, in which case the pomodoro is reset.

Therefore, say Jim comes and says hello, while you've got a pomodorro running. You go, "Ah, Jim! One sec." You save everything and close the coding window you were working on, take your headphones off, visibly reset the pomodorro, and rise to greet. If he asks what's that you say exactly what it is. You don't have to be passive aggressive, but explain that it is there to ensure uninterrupted focus, but, oh well it's ok, but, actually if you don't mind, if you see me doing a pomodorro next time please don't interrupt because it means I'm trying to focus ... but if I'm not doing one please do come and say hi".

The pomodorro then becomes a real-life "Status: Busy" icon for your coworkers, and it not ticking becomes a real-life "Available for Chat" icon :p

Of course, there will always be the odd toxic co-worker who pretends not to get it and interrupts anyway, but presumably your question was more general. But in that case, you should be assertive and straightforward about it: "please don't interrupt when I'm doing a pomoddoro, it's severely disrupting my thoughts and takes me forever to get back to that point".

Also, if you're going to use a pomodoro, make sure it reflects reality. If you've got one running but you're clearly playing solitaire, pretty soon it will cease to be a valid marker to your coworkers and they'll ignore it. Not to mention, sticking to pomodorros can be a great productivity and time management tool, so you should stick to it anyway.

I also worked in similar companies in the past (it was Kazakhstan), where we supposed to shake hands (only men). My solution for this was insisting on waving (works when you arrive later), and sooner or later people would start to pick up this method because it's probably problematic to everyone involved.