Means for checking the correctness of a cryptographic operation on an elliptic curve E(Z/pZ), including fault-resistant computation of Q=kP on elliptic curve E(Z/pZ). Elliptic curve E^(Z/pr2Z)≡E(Z/pZ)×E(Z/r2Z) is given by Chinese remaindering and where r is an integer. A point P^=CRT(P (mod p), R (mod r2)) is formed in E^(Z/pr2Z); P^ reduces to P in E(Z/pZ), and to R in E1(Z/r2Z). Q^=kP^ in E^(Z/pr2Z) is computed (130). It is then verified whether Q^≡kR (mod r2) in E1(Z/r2Z), and if so, Q=Q^ mod p is output, whereas “error” is returned if this is not the case. Also provided are an apparatus and a computer program product.