one of the documented procedures in this installation of the ACS
ad_generate_random_string   { length "8" }
What it does:
Generates a random string made of numbers and letters
Defined in: /web/philip/packages/acs-core/security-procs.tcl

Source code:

    set password ""

    set character_list [list a b c d e f g h i j k m n p q r s t u v w x y z A B C D E F G H I J K L M N P Q R S T U V W X Y Z 2 3 4 5 6 7 8 9]

    for {set random_string_counter 0} {$random_string_counter < $length} {incr random_string_counter } {
	set chosen_index [randomRange [llength $character_list]]
	append password [lindex $character_list $chosen_index]
    return $password