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We provide a new identification protocol and new signature schemes based on isogeny problems. Our identification protocol relies on the hardness of the endomorphism ring computation problem, arguably the hardest of all problems in this area, whereas the only previous scheme based on isogenies (due to De Feo, Jao and Plût) relied on potentially easier problems. The protocol makes novel use of an algorithm of Kohel-Lauter-Petit-Tignol for the quaternion version of the -isogeny problem, for which we provide a more complete description and analysis. Our new signature schemes are derived from the identification protocols using the Fiat-Shamir (respectively, Unruh) transforms for classical (respectively, post-quantum) security. We study their efficiency, highlighting very small key sizes and reasonably efficient signing and verification algorithms.