Combine salt, sugar, juniper berries and peppercorns. Rub the flesh side of the salmon with salt mixture. Sprinkle remaining salt mixture in glass dish; lay salmon flesh side down in salt mixture. Cover with plastic wrap. Refrigerate for at least 24 hours and up to 3 days, basting with brine that accumulates in dish. Drain excess liquid from crème fraîche in coffee-filter-lined strainer overnight in refrigerator. Combine thickened crème fraîche, caviar, lemon zest, lemon juice, cucumber, thyme and chives.