Page 329 - Hardware Implementation of Finite-Field Arithmetic

An Example of Application—Elliptic Curve Cryptography 309

xor_gates: for i in 0 to m-1 generate
xxPxoryyP(i) <=xxP(i) xor yyP(i);
end generate;
with sel_1 select y1 <= yyP when ‘0’, xxPxoryyP when
others;
with sel_2 select next_yQ <= y3 when “00”, yyP when “01”,
xxPxoryyP when others;
with sel_2 select next_xQ <= x3 when “00”, xxP when
others;
first_component: K163_addition port map(
x1 => xxP, y1 => y1, x2 => xQ, y2 => yQ, clk => clk,
reset => reset, start => start_addition, x3 => x3,
y3 => y3, done => addition_done
);
second_component: classic_squarer port map(
a => xxP, c => square_xxP
);
third_component: classic_squarer port map(
a => yyP, c => square_yyP
);
register_P: process(clk)
begin
if clk’ event and clk = ‘1’ then
if load = ‘1’ then xxP <= xP; yyP <= yP;
elsif ce_P = ‘1’ then xxP <= square_xxP;
yyP <= square_yyP;
end if;
end if;
end process;
register_Q: process(clk)
begin
if clk’ event and clk = ‘1’ then
if load = ‘1’ then Q_infinity <= ‘1’;
elsif ce_Q = ‘1’ then xQ <= next_xQ; yQ <= next_yQ;
Q_infinity <= ‘0’;
end if;
end if;
end process;
divide_by_2: for i in 0 to m-1 generate
a_div_2(i) <= a(i + 1);
end generate;
a_div_2(m) <= a(m);
next_a <= (b(m-1)&b) + a_div_2 + carry;
next_b <= zero - (a_div_2(m-1 downto 0) + carry);
register_ab: process(clk)
begin
if clk’ event and clk = ‘1’ then
if load = ‘1’ then a <= (‘0’&k); b <= zero;
elsif ce_ab = ‘1’ then a <= next_a; b <= next_b;
end if;
end if;
end process;
aEqual0 <= ‘1’ when a = 0 else ‘0’;