Suggesstion: Use hexadecimal AccountID instead of base64

[dogtopus]

Although a bit longer than base64 (16 vs 12), hexadecimal should be easier to type on phones since only digits and letter a-f are used and it's also case insensitive. In comparison base64 uses digits, both upper and lower case letters, 2 symbols and a = (!).

Also since PSVita backups also use the AccountID in hexadecimal as the folder name, users who backed up their Vita before (for backup or CFW installation) could just copy and paste the ID directly to Chiaki without using any helper script, which is really convenient IMO.