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Oblivious Transfer

Jenna Phipps
Last Updated May 24, 2021 8:02 am

Oblivious transfer (OT) is a protocol used in cryptography between parties who do not trust each other. It is an attempt to prevent cheating by maintaining security while creating a secret encryption key. Oblivious transfer means that one party passes multiple messages to another without knowing which message is then accepted. For example, if Alice and Bob use the all-or-nothing oblivious transfer protocol, Alice will send a message to Bob through an established communication channel but will not know whether Bob received that message.

Another popular oblivious transfer protocol is the one-out-of-two (or 1-2) protocol. In this procedure, Alice sends two messages to Bob, who can only read one. She does not know which. Bob will receive one message, and from there he and Alice will complete different algorithms to establish a secure channel: he will receive a private key. When Alice sends encrypted messages, Bob will be able to decrypt the correct message using the key that they created.

Researchers have applied quantum cryptography principles to oblivious transfer because oblivious transfer as a cryptographic primitive has been susceptible to attacks from quantum computers. However, researchers have shown that even quantum OT is not unconditionally secure. Lo’s no-go theorem, for example, showed that quantum encryption cannot unconditionally secure an oblivious transfer on its own. However, OT is a helpful technique for creating a transmission channel between two mistrustful parties.