The Gospel of Judas is believed to have been written during the latter part of the 2nd century, so it could not be written by Judas, circa 30 AD. One has to reject the canonical gospels in order to accept this one because the Gospel of Judas shows him as being obedient to Jesus and not disobedient.
In the 2nd century a Bishop of the Church, Irenaeus, spoke of this heretic writing from a sect called the Cainites, saying this:
"Others again declare that Cain derived his being from the Power above, and acknowledge that Esau, Korah, the Sodomites, and all such persons, are related to themselves. On this account, they add, they have been assailed by the Creator, yet no one of them has suffered injury. For Sophia was in the habit of carrying off that which belonged to her from them to herself. They declare that Judas the traitor was thoroughly acquainted with these things, and that he alone, knowing the truth as no others did, accomplished the mystery of the betrayal; by him all things, both earthly and heavenly, were thus thrown into confusion. They produce a fictitious history of this kind, which they style the Gospel of Judas."