Classic protocol and crypto cleanups.

Duplication, see first test after the nparam != 5 block containing this.

I would be inclined to, right after sscanf,
```
const bool badcmd = nparam > 0 && strcmp(sauth, "SAUTH");
const bool badparam = nparam < 5;
if (badparam) { Log(...); }
if (badcmd) { Log(...); }
if (badparam || badcmd) { return false; }
```