https://github.com/merbanan/rtl_433/issues/1820: OOK, Manchester encoded,
50 us half-bit signal mistaken for XOR/stream-cipher encryption for years,
since only a tail-byte and a low-nibble check were ever confirmed.
B3 and B4 are each an affine function of B0 (B3 = B0 - k1, B4 = k2 - B0),
making (B3 + B4) mod 256 a fixed per-unit checksum. Two physical sensor
units are confirmed in the issue's captures, with checksums 0x41 and
0x3c; both are recognized here.
Verified against all 9 real packets in samples2.zip plus 37 codes derived
from a separate text dump in the issue, cross-checked byte-for-byte
against the community's own manual decode posted in the thread.
No temperature/pressure mapping: no capture in the issue pairs a raw code
with a numeric ground-truth reading, so only the validated raw code is
output for now.
9851e7bdcb