Given that http is plaintext in the clear, and uqrto fcsm seems to have letter patterns similar to English, a is a likely candidate.
u (21) → 21-3=18 → r q (17) → 14 → n r (18) → 15 → o t (20) → 17 → q o (15) → 12 → l → rnoql — no.
u (21) → 21-3=18 → r q (17) → 14 → n r (18) → 15 → o t (20) → 17 → q o (15) → 12 → l → rnoql — no. http uqrto fcsm