Gemara

Beraisa - R. Yishmael): If a Yisrael and a Nochri [extortionist] came for judgment, If Torah law favors the Yisrael, we rule like Torah law. If Nochri law favors the Yisrael, we rule like Nochri law. If neither favors the Yisrael, we seek a ruse (to exempt the Yisrael);

R. Akiva says, we may not seek a ruse. This is not Kidush Hash-m!

Inference: If not for Kidush Hash-m, we could use a ruse!

Question: One may not steal from Nochrim!

(Beraisa - R. Shimon citing R. Akiva): The law of a Yisrael slave sold to a Nochri teaches that one may not steal from Nochrim. "He will have redemption" - we may not forcibly take him without paying.

Suggestion: Perhaps he may trick him!

Rejection: "V'Chishev Im Konehu" - he will calculate with the buyer, i.e. precisely.

Answer (Rava): It is forbidden to steal from a Nochri, but one may use a ruse to evade paying a debt to a Nochri.

Bechoros 13b (Ameimar): A Nochri acquires and is Makneh through Meshichah (taking to one's premises).

Question: According to R. Yochanan, mid'Oraisa, a Yisrael acquires through money. "V'Chi Simkero Mimkar la'Amisecha" teaches that a Nochri does not acquire through money, rather, through Meshichah. However, according to Reish Lakish, mid'Oraisa, (also) a Yisrael acquires through Meshichah. How does he expound "Amisecha"?

Answer: "La'Amisecha... Al Tonu" obligates returning Ona'ah (an overcharge) to a Yisrael, but not to a Nochri.

Question: According to the opinion that permits Gezel Nochri, there is no need to teach that Ona'ah does not apply to Nochrim!

Answer: Indeed, if Ameimar permits Gezel Nochri, he must hold like R. Yochanan.

Rishonim

Rif and Rosh (10:12): Gezel Nochri is forbidden.

Rambam (Hilchos Gezeilah 1:2): Mid'Oraisa, it is forbidden to steal any amount. One may not steal or be Oshek even a Nochri idolator. If one did, he must return it.

Poskim

Rema (EH 28:1): If one was Mekadesh a woman with Gezel or Geneivas Nochri, she is Mekudeshes, since he must return it only due to Kidush Hash-m (Mahari Veil 138).

Question (to Mahari Veil): Yitzchak sold a (Nochri's) security to Mordechai, and Mordechai was Mekadesh a woman with it. Is this like Gezel Nochri, i.e. Gezel mid'Rabanan, so the Kidushin is invalid, like one who was Mekadesh with Chametz mid'Rabanan?

Rebuttal (Mahari Veil 138): This (selling a security) is unlike Gezel Nochri. Gezel is only like "he stole the spear (from the Mitzri's hand)"! Rather, it is like uprooting a Nochri's loan, which is permitted. Even though it is forbidden where there would be Chilul Hash-m, perhaps it is not considered theft! Chazal forbade many things l'Chatchilah, e.g. Avak Ribis, but b'Di'eved one need not return them. Surely, if one was Mekadesh with Avak Ribis she is Mekudeshes! I say that here, it is full Kidushin. Yitzchak intended to sell the security absolutely. Even though a lender does not acquire a Nochri's security, he can scheme to evade the Nochri, e.g. he will say that it was lost, then it is permitted in his hand. Perhaps there is no Chilul Hash-m in this. Yitzchak intended for a full sale, and he will settle with the Nochri (so the Nochri will have no further claim to his security), to preserve his own integrity. Also, perhaps Gezel Nochri need not be returned.

Rebuttal (of Rema - Shach CM 348:2): The Shulchan Aruch (CM 348:2, 359:1) connotes that Gezel Nochri is forbidden mid'Oraisa. The Yam Shel Shlomo says that the Rambam, Tur and Semag say so. Why does the Rema here disagree, and require returning it only due to Kidush Hash-m? He cites Mahari Veil, but Mahari Veil does not say so!

Defense (Nesivos ha'Mishpat 348:1): Even though the Torah forbids Gezel Nochri, one must return even to a Yisrael only due to "v'Heshiv Es ha'Gezeilah". One must return to a Nochri only due to Chilul Hash-m. "Amisecha" exempts from returning Ona'ah to a Nochri (Bechoros 13b). Indeed, without a Drashah we would say that the Mitzvah to return applies even to Nochrim. However, since a verse exempts from returning Ona'ah to a Nochri, we would learn from there to permit Gezel Nochri, if not for "v'Chishev" to forbid. Since v'Chishev does not teach that one must return Gezel Nochri, the Mitzvah to return it is only mid'Rabanan.

Etzei Arazim (4, cited in Hagahos Ma'aseh Nisim 2): In the Parshah of returning theft, it says "Amiso", to exclude Nochrim.

Chelkas Mechokek (3): The Rema connotes that this is even before despair, for she needs to return it only due to Chilul Hash-m. This requires investigation. The Gemara connotes that the Torah forbids Gezel Nochri, just there is no Kefel, for it says "Re'ehu". What is the source to exempt from returning Gezel Nochri while it is intact without despair? The Gemara does not allude to a difference between Yisrael and Nochrim regarding this. Perhaps this is only for absolute theft, but not for sale of a security which the Yisrael received b'Heter, which is like uprooting a loan. I say that Kidushin with Gezel Nochri is only mid'Rabanan, and if another was Mekadesh her, she needs a Get.

Beis Shmuel (5): All agree that one who bought Gezel Nochri does not transgress mid'Oraisa, for Oshek is only mid'Rabanan because it came to his hand b'Heter. The same applies here. This answers the contradiction in the Rema. However, he should be obligated to return it mid'Rabanan, just like Oshek, not only due to Chilul Hash-m.

Gra (5): The Yerushalmi (Bava Kama 4:3) says that two Nochri officers were sent to learn Torah. They concluded that it is all true, except that one may steal only from a Nochri, but not from a Yisrael (and one other law). R. Gamliel decreed at that time to forbid Gezel Nochri, due to Chilul Hash-m. This is like the opinion that permits Gezel Nochri (mid'Oraisa). Mahari Veil discusses uprooting a loan (which is forbidden only when there is Chilul Hash-m). The Rema learns to all Gezel Nochri; this is wrong.

Magen Avraham (637:3): A Sukah in Reshus ha'Rabim is Sukah Gezulah!! Even if all Yisre'elim pardon this, Nochrim do not. B'Di'eved it is Kosher. Even though we forbid Gezel Nochri, it is not Mitzvah ha'Ba'ah b'Aveirah. The Yere'im say that even the one who permits Gezel Nochri holds that it is not yours.

Chazon Ish (EH 38:17): We learn from the Rema that if there is no Isur Gezel, it belongs to the thief and he can be Mekadesh with it. This is unlike the Yere'im. It is lost from the Nochri. A person taking it is like a river taking it, even according to the opinion that forbids Gezel Nochri!

Nesivos ha'Mishpat (348:1): Since he caused that she may benefit from the theft, she is Mekudeshes. The Ran (Kidushin 23a DH Machran) says that this is why Kidushin with something exchanged for Isur Hana'ah takes effect.