“Now the betrayer

Had given them

A sign.

He said.

‘The one

I will kiss

Is the man.

Seize him!’

Judas

Suddenly came up

To Jesus.

He said.

‘Greetings!

Rabbi!”

Then he kissed him.”

ὁ δὲ παραδιδοὺς αὐτὸν ἔδωκεν αὐτοῖς σημεῖον λέγων Ὃν ἂν φιλήσω αὐτός ἐστιν· κρατήσατε αὐτόν.

καὶ εὐθέως προσελθὼν τῷ Ἰησοῦ εἶπεν Χαῖρε, Ῥαββεί, καὶ κατεφίλησεν αὐτόν.

This is almost word for word in Mark, chapter 14:44-45.  In Luke, chapter 22:47, there is an abbreviated form of only Judas kissing Jesus, while in John, chapter 18, there is no Judas kiss at all.  It is interesting to note that John left this out in his otherwise well detailed description.  Both Mark and Matthew said that this betrayer of Jesus (ὁ δὲ παραδιδοὺς αὐτὸν), Judas, had given the crowd a sign (ἔδωκεν αὐτοῖς σημεῖον).  Judas had told them that the one that he kissed (λέγων Ὃν ἂν φιλήσω) would be the man to seize or hold (αὐτός ἐστιν· κρατήσατε αὐτόν).  Thus, Judas suddenly came up to Jesus (καὶ εὐθέως προσελθὼν τῷ Ἰησοῦ).  Then he said “Greetings (εἶπεν Χαῖρε)!  Rabbi (Ῥαββεί)!”  Then he kissed Jesus (καὶ κατεφίλησεν αὐτόν).  Notice that both Matthew and Mark used the Jewish title of Rabbi, a term that Matthew did not approve of.  The kiss would have been the normal greeting and was certainly used by his followers as indicated in the Pauline letters.