struct.sv

typedef struct {
    logic [255:0] msg;
    logic [255:0] key;
    logic [255:0] modulus;
} StructType;

module TestMod (
    input logic clk,
    StructType in
);

logic [255:0] msg;
logic [255:0] key;
logic [255:0] modulus;

always_ff @( posedge clk ) begin
    msg <= in.msg;
    key <= in.key;
    modulus <= in.modulus;
end

endmodule