What functional encryption scheme can be used to compute a linear function?

I am looking for a functional encryption scheme that can compute a linear function. I do not need to work with attributes.

All I want is to compute the result of a function $y = a*x+b$, where $x$ is the hidden value, which I don't want to reveal.

• Can your linear function be represented as a matrix? If so, you might be able to get away with something simpler like inner-product encryption to multiply your matrix (i.e. evaluate your linear function) on a value (vector) in the message space. – pg1989 Apr 26 '16 at 21:36
• By 'inner-product encryption' I mean an encryption which supports inner product computation on ciphertexts. – pg1989 Apr 26 '16 at 21:37
• iacr.org/archive/eurocrypt2008/49650145/49650145.pdf – pg1989 Apr 26 '16 at 21:38
• @pg1989, the functionality I want to implement is like this : F : K x Z -> Z, K - the space of party's secret key, Z - the set of integers and the ciphertext space. In my case, K = Z. – guglielmo london Apr 26 '16 at 22:14
• Well, the trivial solution is letting outer_encryption_(m) be ​ prefixfree(inner_encryption_(m)) || linear_function_(m) . ​ ​ ​ If that doesn't work, then you should try clarifying what you're after. ​ ​ ​ ​ ​ ​ ​ ​ – user991 Apr 27 '16 at 0:07