Jesus did not write down anything. Everything is second-hand account.

SO, technically, you do not question the authenticity of what Christ teaches, you question the authenticity of second-hand accounts.

Only technically speaking, of course - along the same line of doubting as the translations from Hebrew to Greek to English, from a distance of centuries.

What you cannot question is more important than authenticity, its the validity of the teachings. It stood the test of time like no other, and its becoming more relevant.

Christ is the Son of God, it cannot be doubt.