Retrieved 31 October 2016. ↑ Abusalah, Hamza; Alwen, Jo\"{e}l; Cohen, Bram; Khilko, Danylo; Pietrzak, Krzysztof; Reyzin, Leonid (2017). "Beyond Hellman's Time-Memory Trade-Offs with Applications to Proofs of Space" (PDF). {{cite journal}}: Cite journal requires |journal= (help) ↑ Cohen, Bram; Pietrzak, Krzysztof. "Simple Proofs of Sequential Work" (PDF).