Heat the vinegar, sugar and a splash of water in a small saucepan just long enough to dissolve the sugar. Transfer to a small serving bowl and let cool.
Peel the cucumber, then grate it on the large holes of a box grater or in a food processor using the shredding disk, or with a mandoline. Place the cucumber in a sieve and season with sea salt. Let drain for 20 to 30 minutes.
Press the liquid from the cucumber, and then add the cucumber to the bowl with the vinegar mixture. Stir in the creme fraiche and season with white pepper. Adjust the salt and pepper to taste.