DFC cipher uses affine transformations mod $2^{64}+13$. 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.
Consider a cipher which is using affine transformations mod $2^{128}$. Is it still (it was 20 years ago) a problem to implement it securely? Will affine transformations mod $2^{64}$ make a big difference?