I permanently need to hash lots of data quickly, but the result only needs to be collision resistant.
Is there any negative side-effect of using multiple (say 2) algorithms providing a shorter digest (e.g. RIPE-MD-128 and Tiger128) versus using an algorithm providing a digest of the added length (e.g. SHA256).
I want to explicitly highlight that I only need high performance and collision resistance. Other properties (avalanching, etc.) are irrelevant, I do not even care if it is possible to go back from digest to input. So I do not even need to really use "cryptographic" hashing algorithms (CRC32 is perfectly fine here I guess).
More specifically my idea is to use multiple REALLY FAST algorithms (clhash performing at over 4 gigabyte per second on my testsetup, xxhash performing at over 6GB/s, ...) and simply concatenate them to improve collision resistance: $$ Digest(Input) = XXH64(input)\ |\ CLhash(input)\ |\ CRC32(input)\ |\ Farsh(input) $$
This results in a digest with $64+64+32+32=192$ bits length, but is faster than an algorithms providing a digest with 192 bits. The important question for me is: is the collision resistance comparable to an algorithm providing 192 bits?
I benchmarked a lot of different hashing algorithms and the fastest performing hash, that is also reviewed and provides a long digest (which can be an indicator of better collision resistance), is Blake2b performing slightly above 1500 megabytes per second and provides a 512 bit digest. A combination of different algorithms would be even faster, and for my use case performance is key.