# How to compute an identity function on encrypted vector by using a third party?

I want to compute an identity function over encrypted vector on a third party. For example, F(x) = [a1,a2,..,an] where x is a tag. However, i do not want the third party to fetch over the whole dataset to found the needed Vector.

So, is there is any encryption scheme that can do this ?

• Welcome to crypto.SE. Sorry, but many things are unclear. "identity", "tag", and the desired/assumed relationship between x and F(x). If F(x)=x (a reasonable guess for identity), that means a tag is a vector? In what set are a1..an? – fgrieu Apr 7 at 18:06
• The identity function most commonly refers to the function $F(x) = x$, for all $x$. Do you rather mean the function $F(x) = a_x$ (where $[a_1, a_2, …, a_n]$ is a known (to the server) vector? – poncho Apr 7 at 18:06
• Thank you. In my case, i means by tag a label or an atribute that identifies a vector of data. The function f is the function that search over the dataset vectors and returns the Vector identifed by the tag x. However, the function f is generated by the user not the third party and the third party just performs the function and returns the result of this function. – sof Apr 7 at 18:20
• Sorry, but it's not clear what you are asking about. You might be well-served by explicitly laying out how knows what, both before and after the exchange... – poncho Apr 7 at 19:24