Blown up deadline and I choose a large bite to chew For my master's thesis at a Greek University, I proposed to my supervisor to do end-to-end encryption of multiparty situations. I chose my topic because I had a plan for a post-master project and thought I can do bibliographic research through my master thesis. I presented this long-term project to my supervisor in an earlier semester essay.

On mid-term, my supervisor told me that bibliographic research was not enough. I suggested implementing an existing end-to-end group key agreement in javascript (having on my back of my head as a possible software stack t my project) and I laid down a timeframe. 

I did manage to make a program but even though I tried my best to implement it I could not find a solution. Also due to time limitations and lack of any help (including from my supervisor), I found it too hard to approach it in a timely manner because I have to put together the pieces for the final thesis text as well.

But instead, I did manage to have an initial overlay architecture and requirements for my own long-term project by doing the literature review.

So I thought: "I can be honest and tell whatever happened about what I did manage to understand through the literature review, what gaps I found, lay down the initial architecture for my long-term project and present to the thesis examiners at the thesis examination what I did and why I failed and show them that I tried hard to achieve that."

Is this sufficient to get a master's degree, or will my attempt at honesty hurt me?
Just narrow the scope.  It is normal for students (and advisors) to make too broad of a scope.  As they get into a topic, they realize it is too much "real estate" to cover.  

Personally, I would just write up what you have and modify the introduction to have a smaller objective.  But perhaps things are more strict in Europe.  But it would be very normal for a US doctorate thesis, even, to morph quite a bit.  

The other advantage of writing up what you have is that you (and the advisor) are then looking at a tangible object.  Versus arguing about something in the abstract.  When you both look at it physically, it may look like enough.  Plus you need to write it anyways...so it doesn't hurt you, the time to do it.  [This applies to the work world as well.  Don't underestimate the value of a "half a loaf", especially a tangible one that you are looking at.]