This procedure is defined in the server but not documented via ad_proc or proc_doc and may be intended as a private interface.
The procedure is defined as:
proc nsmcp::accessTimeIndexKey {file} {
return [ns_crypto::md string -digest sha256 -- [list access-time-index-v2 [dict get $file identity] [dict get $file compressed] [::nsmcp::accessRecordParser cget -timingColumn]]]
}