Techniques allegedly included electric shock treatment, sexual and water torture and nearly 300 cases of "roller" abuse in which a round metal object is placed on the thighs of a sitting detainee and then sat on by guards to crush the muscles.
The ICRC said it had been "forced to conclude that the (Indian government) condones torture," the cables said.
Human rights groups have repeatedly accused the government of abuses in Kashmir, where it has been fighting an armed separatist insurgency for more than 20 years.
The ICRC, which met with nearly 1,500 detainees, stressed that very few were militants.
The vast majority were civilians "connected to or believed to have information about the insurgency".
It also noted that all the branches of the security forces used torture techniques and always in the presence of an officer.
The cables concluded that the evidence of ill-treatment and torture was "very disturbing".
Militant violence in Kashmir has eased since nuclear-armed India and Pakistan launched a peace process in 2004 over the disputed Himalayan region.
But popular pro-independence protests since June have left more than 110 protesters and bystanders -- many of them teenagers and young boys -- dead.
India and Pakistan each hold part of Kashmir but claim it in full.