Adi Shamir

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A co-founder of cybersecurity company RSA who also co-developed its public key cryptography algorithm couldn't make it to the RSA Conference in San Francisco this year. It seems he couldn't get a visa from the US government.

In a video message played at the major cybersecurity gathering, Israeli cryptography expert Adi Shamir -- the "S" in RSA -- said he hadn't received a response to his request for a tourist visa, despite having applied two months ago.

Shamir also suggested that if he, a well-known and award-winning security expert, couldn't get a US visa, then it might be time to rethink where scientific conferences are held.

Shamir is the Borman Professor of Computer Science at Israel's Weizmann Institute. He's well-known for his work on the RSA cryptosystem as well as identity-based cryptography. He's also a regular speaker on the cryptographers panel at the RSA conference each year.

The Department of State declined to comment. Shamir didn't respond to a request for comment.

Some Twitter users are shocked by Shamir's situation, saying it's "unbelievable" he couldn't attend the conference.