7 character extraction from string (Cert subject)

if the last blank is always before the 7 Chars use the following simple irule line :

set last7Chars [string last " " [X509::subject [SSL::cert 0] end]

Otherwise:

set certSubject [X509::subject [SSL::cert 0]]
set lenSubject [string length $certSubject]
set last7Location [expr {$lenSubject - 8}] 
set last7Chars [substr $certSubject $last7Location 7]