This might be a dumb question but I will go for it.

Let say we have a data set D consisting of sensitive data, and we want to be able to match if a new piece of data S already exists in D or not, and we want to be able to know which of the entries matches S in D.

Our approach consisted of a 1-way cryptographic hash such as SHA256. However, since the dataset is relatively small (about 4 million rows) we can easily reproduce the full dataset and in effect "decode" the original meaning of the hash.

So I was wondering if it exists and algorithm that takes two parameters

• d: some sensitive data and
• s_i: a random salt i

a cryptographic algorithm C and a comparator M such that

M(C(d, s_1), C(d, s_2)) = true

So those such an algorithm exists or something like it?