The certificate for verifying the signature of the barcode printed on the Arrival Attestation document (valid since 22nd October 2020) has the SHA-256 fingerprint:
CD 5B CA A6 2D 5B 61 39 07 B9 38 EC 52 35 6A 49 89 BD 80 53 2B EB 08 C1 E7 18 96 F7 B1 53 A3 F7