t (20) → t(20) to t(20) = shift 0? no.
However, based on the phrase "Download- ..." possibly the decoded text is something like: Download- tjmyt nwdz lbt sghyrt wtkt tql wtqfsh...
It looks like the string you provided — "Download- tjmyt nwdz lbt sghyrt wtkt tql wtqfsh..." — is not in plain English. It appears to be encoded, possibly with a simple substitution cipher like or an Atbash cipher . t (20) → t(20) to t(20) = shift 0
Shift -5 seems wrong. tjmyt: t(20)-3=17=q, j(10)-3=7=g, m(13)-3=10=j, y(25)-3=22=v, t(20)-3=17=q → "qgjvq" no. Step 4 — Atbash (a<->z, b<->y…) t(20)<->g(7) j(10)<->q(17) m(13)<->n(14) y(25)<->b(2) t(20)<->g(7) → "gqnbg" not good. Given the lack of a clear result after testing common ciphers, I can’t complete a content review of the decoded message without the key. Download- tjmyt nwdz lbt sghyrt wtkt tql wtqfsh...