SAN FRANCISCO — A decision last week by a federal magistrate judge ordering a criminal defendant to decrypt his devices could mark an important shift in Fifth Amendment law in favor of greater government access to encrypted data.

The ruling by U.S. Magistrate Judge Jacqueline Scott Corley of the Northern District of California is not the first time a defendant has been ordered to decrypt his device under what is known as the “foregone conclusion” exception to the Fifth Amendment. But Corley’s legal reasoning, if upheld, would make it significantly easier for law enforcement to get similar orders in the future, according to legal experts.