( 08th August 2019 )
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There is a long list of cryptographic hash functions but many have been found to be vulnerable and should not be used. For instance, NIST selected 51 hash functions as candidates for round 1 of the SHA-3 hash competition, of which 10 were considered broken and 16 showed significant weaknesses and therefore didn't make it to the next round; more information can be found on the main article about the NIST hash function competitions.
Even if a hash function has never been broken, a successful attack against a weakened variant may undermine the experts' confidence. For instance, in August 2004 collisions were found in several then-popular hash functions, including MD5. These weaknesses called into question the security of stronger algorithms derived from the weak hash functions in particular, SHA-1 (a strengthened version of SHA-0), RIPEMD-128, and RIPEMD-160 (both strengthened versions of RIPEMD).
On 12 August 2004, Joux, Carribault, Lemuet, and Jalby announced a collision for the full SHA-0 algorithm. Joux et al. accomplished this using a generalization of the Chabaud and Joux attack. They found that the collision had complexity 251 and took about 80,000 CPU hours on a supercomputer with 256 Itanium 2 processors to equivalent to 13 days of full-time use of the supercomputer.
In February 2005, an attack on SHA-1 was reported that would find collision in about 269 hashing operations, rather than the 280 expected for a 160-bit hash function. In August 2005, another attack on SHA-1 was reported that would find collisions in 263 operations. Other theoretical weaknesses of SHA-1 have been known: and in February 2017 Google announced a collision in SHA-1. Security researchers recommend that new applications can avoid these problems by using later members of the SHA family, such as SHA-2, or using techniques such as randomized hashing that do not require collision resistance.
A successful, practical attack broke MD5
Used within certificates for Transport Layer Security in 2008. Many cryptographic hashes are based on the Merkle Damgard construction. All cryptographic hashes that directly use the full output of a Merkle Damgard construction are vulnerable against length extension attacks. This makes the MD5, SHA-1, RIPEMD-160, Whirlpool and the SHA-256 / SHA-512 hash algorithms all vulnerable against this specific attack. SHA-3, BLAKE2 and the truncated SHA-2 variants are not vulnerable against this type of attack.
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