As the use of contraband rule clarification stated, Sec cannot use the contraband from an uplink if found unlocked. But according to the same crew can operate uplinks if discovered.
Which means that syndicate encryption is considered contraband, however i see sec and honestly including myself either buying keys from open uplinks or extracting them from headsets as non antags to “tap” the line and allow to find syndicates. Though that also means it would be considered use of contraband