Some embodiments are directed to a cryptographic device (20). A reliable bit function may be applied to a raw shared key (k*) to obtain reliable indices, indicating coefficients of a raw shared key, and reliable bits derived from the indicated coefficients. Reconciliation data (h) may be generated for the indicated coefficients of the raw shared key. A code word may be encapsulated using the reliable bits by applying an encapsulation function, obtaining encapsulated data (c) which may be transferred.