Does RSA operate over a Finite Field (Galois Field)? Is it correct to say that RSA operates over a Finite Field (Galois Field)? In this case GF(p)?
I do understant that the modulo in RSA is not itself a prime number, but all the operations (multiplication, inversion) occur as if it is a GF(p).
No, RSA encryption and signature is performed in (the multiplicative semigroup of) the factor ring $\mathbb Z/n\mathbb Z$ which is not a field since the non-zero elements $kp+n\mathbb Z$ (for $0&lt;k&lt;q$) and $kq+n\mathbb Z$ (for $0&lt;k&lt;p$) do not have multiplicative inverses. (However, one easily observes that all other non-zero elements are invertible, as their representants are coprime to $n=pq$).