Rif Gittin 3b {10b}

3b

{Gittin 10b}

והלכתא עידי הגט אין חותמין אלא זה בפני זה
מ"ט א"ר אשי גזרה משום כולכם

And the halacha {taken from Rav Papa} is that the witnesses to a get only sign in each other's presence.
What is the reason? Rav Ashi said: As a decree because of "all of you."
{That if he says to ten people "all of you write," one writes and the other sign in each other's presence.}

Mishna:

כל השטרות העולין בערכאות של עובדי כוכבי' אע"פ שחותמיהם עובדי כוכבים כשרים חוץ מגיטי נשים ושחרורי עבדים
ר"ש אומר אף אלו כשרים לא הוזכרו אלא בזמן שנעשו בהדיוט

ALL DOCUMENTS WHICH ARE ACCEPTED IN HEATHEN COURTS, EVEN IF THEY THAT SIGNED THEM WERE GENTILES, ARE VALID [FOR JEWISH COURTS] EXCEPT WRITS OF DIVORCE AND OF EMANCIPATION.

RABBI SHIMON SAYS: THESE ALSO ARE VALID; THEY WERE ONLY PRONOUNCED [TO BE INVALID] WHEN DRAWN UP BY UNAUTHORISED PERSONS.