Abstract: We present the cryptographic hash function BLAKE2, an improved version of the SHA-3 ﬁnalist BLAKE optimized for speed in software. Target applications include cloud storage, intrusion detection, or version control systems. BLAKE2 comes in two main ﬂavors: BLAKE2b is optimized for 64-bit platforms, and BLAKE2s for smaller architectures. On 64-bit platforms, BLAKE2 is often faster than MD5, yet provides security similar to that of SHA-3. We specify parallel versions BLAKE2bp and BLAKE2sp that are up to 4 and 8 times faster, by taking advantage of SIMD and/or multiple cores. BLAKE2 has more beneﬁts than just speed: BLAKE2 uses up to 32% less RAM than BLAKE, and comes with a comprehensive tree-hashing mode as well as an efﬁcient MAC mode.