The phrase "secret channel" is correct and usable in written English.
For example, you could use it in a sentence like: "The hackers were able to infiltrate our system through a secret channel that we were unaware of."
Novartis responded by opening up a secret channel of discussion with the campaign.
They're encoded in a secret channel that every local broadcaster transmits.
And, last year, he authorized a secret channel, in Oman, that seeded the current public talks.
Eventually, though, these discussions prompted the imprisoned leaders of Al Jihad to open their own secret channel with the government.
According to Western officials, Miliband and other British officials have urged the Obama Administration to authorize the C.I.A. to open a secret channel of communication to the Taliban.
It was like a hidden passage on Wall Street, a secret channel that enabled billions of dollars to flow through Lehman Brothers.
The plaintiffs were paid through complex and secret channels, involving a safe hidden in Mr Bershad's office, other law firms and even casinos.
The intelligence operations of the Great Powers also included secret channels of communication, the penetration of émigré circles, and the assassination of enemies of the state.
After a U.S. offer of general mediation had miscarried in December 1916, Charles tried through secret channels to deal directly with the Triple Entente powers.
The most difficult issues continue to be worked out through several secret channels between the Israelis and Palestinians, with only unsubstantiated details coming through leaks to the press.
"The sudden departure of Guriev is connected to the attempt to keep out of the hands of investigators these secret channels, through which oligarchic and federal budgetary funds went to support the revolutionary anti-Putin opposition," Mr. Markov said.
