# Hardwired secret key in public / private key encryption

I am new to cryptography and I need to know some details about the hardwired keys.

Taking as an example the paper "Multi-Input Functional Encryption", a key is hardwired in the description of the key generation scheme.

Is this technique related to encryption schemes or it is a form of circuit construction?

“Hardwiring” an input into a (say, Boolean) circuit usually means taking a circuit $$C$$ with two inputs $$x\in\{0,1\}^n$$, $$y\in\{0,1\}^m$$ and then fixing the inputs corresponding to $$y$$. This gives the circuit $$C_y$$ that for every $$x$$ returns $$C(x,y)$$ [AB]. Thus, hardwiring is more about circuits and has nothing to do with encryption schemes.
In the example of multi-input functional encryption, the circuit $$\mathsf{G}_f$$ can be seen as a function that takes a master secret key and $$n$$ ciphertexts as input. By hardwiring a particular $$\mathsf{MSK}$$, you are fixing the first input to the circuit $$\mathsf{G}_f$$ to this $$\mathsf{MSK}$$.