Satan is not omniscient; he did not know God's plan of salvation and that is why he crucified Christ

Omniscience belongs to God alone; Satan cannot be omniscient by definition. Demons in Mark knew who Jesus was but not why He had come ("are you here to torment us before the time?"). Paul writes in 1 Corinthians 2:8 that if the rulers of this age had known, they would not have crucified the Lord of glory. Satan saw the weak human form and thought he had an opportunity to attack God; the crucifixion backfired. When Jesus called Peter "Satan," He was using the term as "adversary" — Peter's opposition to the cross had the same effect as an adversary, not that Peter was possessed.