A common technique used on hard copy terminals to hide entered data such as passwords is the use of a strike-over mask, where two or more lines of characters are printed one over the other, and the print head left underneath these characters. The next line of data typed is then unreadable.
MAI-OC keeps track of where the print head would be on a real hard copy terminal and prevents the echoing to the screen or activity log of all or some of the next line of data sent to the application. Any characters sent that would be underneath other characters are replaced by an asterisk. For example, suppose MAI-OC received the following string of characters from the application:
XXXXXXXX<LLLLLLLL<OOOOOOOO<
Specifies an SCS carriage return (X'0D').
If the MAI-OC user were then to send the characters MYPASSWORD to the application, those characters would be echoed to the screen and log as ********RD, because the first eight characters would be obscured on a real terminal. Multiple backspace characters instead of carriage return could be used in the mask.
An alternative to the use of strike-over masks is the use of the Inhibit and Enable Print SCS control characters.