とすれば is a way to make a supposition. Like "assuming that's the case," so あげたとすれば "assuming [you] gave [it to me]." You could say the next part 法律の上で means "in the eyes of the law."
Try looking up とする, since this is what it stems from, meaning you'll also see it in the other conditional forms. There's also the very useful form として, which means something like 'as/from the perspective of'.
Javizy wrote:Try looking up とする, since this is what it stems from, meaning you'll also see it in the other conditional forms. There's also the very useful form として, which means something like 'as/from the perspective of'.