Yield strength = 300 MPa
Tensile Strength = 600 MPa
Elongation = 50%
Here are the three points you identified (strain, stress)
(0,0)
(0.002,300)
(0.5,600)
If you knew the modulus of elasticity and when the curve first deviated from linear, you could approximate it. I.e., if you knew it was steel you could use around 207 GPa for Young's modulus, and draw a straight line until the curve deviated from linear (proportional limit), then approximate the rest of the points with a smooth curve up to failure (0.5, 600). Austentic stainless steels could have an elastic limit of around 50%, so if you knew this was the class of material you could find some stress strain plots and estimate the proportional limit, and then you would have enough information to estimate such a curve, or you could just "guess" the proportional limit (say 0.005), then that point would be
(0.005, 0.005*207,000)
And you could estimate a curve.