Joseph Rosen (Yiddish: יוסף ראָזין, Yosef Rosin; 1858 – 5 March 1936) known as the Rogatchover Gaon (Genius of Rogachev) and Tzofnath Paneach (Decipherer of Secrets—the title of his main work), was an Ashkenazi rabbi and one of the most prominent talmudic scholars of the early 20th-century.

Rosen was known as a gaon (genius) because of his photographic memory and tendency to connect sources from the Talmud to seemingly unrelated situations.

Joseph Rosen was born in Rogachov, now Belarus, into a Hasidic family of Chabad-Kapust Hasidim,[3] and was educated in the local cheder (elementary school).

[6] Among those who received semikha (rabbinic ordination) from him were Menachem Mendel Schneerson (the seventh Lubavitcher Rebbe, 1902-1994),[7] Mordecai Savitsky (1911-1991) of Boston, Zvi Olshwang (1873–1961) of Chicago (brother-in-law of Shimon Shkop) and Avraham Eliyahu Plotkin (1888-1948; author of Birurei Halachot—a copy of the actual semikha is included in that work).

His main work, a commentary on Maimonides, was published during his lifetime, as were three volumes of halakhic (Jewish law) responsa.

[10] His manuscripts were smuggled out of Latvia in the form of micro photographs sent via mail to the Safern family in the Bronx at the outbreak of World War II by his successor, Yisrael Alter Safern-Fuchs (1911– 20th Sivan, 1942 murdered by the Nazis),[11] who remained in Latvia to complete this task, and his daughter Rachel Citron,[12][13] who had come to Dvinsk from the Land of Israel to help preserve her father's manuscripts.

Kasher, therefore, included Mefa'aneach Tzefunoth (Decipherer of Secrets), an explanatory commentary to facilitate understanding of Rosen's influential work.