 The arbitrary constants, including all entries of the S-box, are derived using the binary expansion of e as a source of "nothing up my sleeve numbers".Soon after DFC's publication, Ian Harvey raised the concern that reduction modulo a 65-bit number was beyond the native capabilities of most platforms, and that careful implementation would be required to protect against side-channel attacks, especially timing attacks.Although DFC was designed using Vaudenay's decorrelation theory to be provably secure against ordinary differential and linear cryptanalysis, in 1999 Lars Knudsen and Vincent Rijmen presented a differential chosen-ciphertext attack that breaks 6 rounds faster than exhaustive search.