请采用verilog实现PRESENT模块，使其31轮每一轮都用随即掩码掩蔽

PRESENT是一种轻量级密码算法，采用SPN结构，其核心部分为S盒和P盒。在实现PRESENT模块时，我们需要先实现S盒和P盒，然后再将它们组合起来实现SPN结构。

以下是一个采用Verilog实现PRESENT模块的示例代码，其中31轮每一轮都使用随机掩码掩蔽。

module present(
    input [63:0] plaintext,
    input [79:0] key,
    output [63:0] ciphertext
);

// 定义S盒
reg [3:0] S[15:0];
initial begin
    S[0] = 4'b0010;
    S[1] = 4'b1100;
    S[2] = 4'b0100;
    S[3] = 4'b0001;
    S[4] = 4'b0111;
    S[5] = 4'b1011;
    S[6] = 4'b1010;
    S[7] = 4'b0110;
    S[8] = 4'b1000;
    S[9] = 4'b0101;
    S[10] = 4'b0011;
    S[11] = 4'b1111;
    S[12] = 4'b1101;
    S[13] = 4'b0000;
    S[14] = 4'b1110;
    S[15] = 4'b1001;
end

// 定义P盒
reg [63:0] P[15:0];
initial begin
    P[0] = 64'h0000000000000000;
    P[1] = 64'h0000000000000001;
    P[2] = 64'h0000000000000100;
    P[3] = 64'h0000000000000101;
    P[4] = 64'h0000000000010000;
    P[5] = 64'h0000000000010001;
    P[6] = 64'h0000000000010100;
    P[7] = 64'h0000000000010101;
    P[8] = 64'h0000000001000000;
    P[9] = 64'h0000000001000001;
    P[10] = 64'h0000000001000100;
    P[11] = 64'h0000000001000101;
    P[12] = 64'h0000000001010000;
    P[13] = 64'h0000000001010001;
    P[14] = 64'h0000000001010100;
    P[15] = 64'h0000000001010101;
end

// 定义轮密钥
reg [79:0] round_key[31:0];
initial begin
    round_key[0] = key;
    for (int i = 1; i < 31; i = i + 1) begin
        round_key[i][79:64] = round_key[i-1][15:0];
        round_key[i][63:0] = {round_key[i-1][79:64], round_key[i-1][63:16]};
        // 使用随机掩码掩蔽
        round_key[i][11:0] = round_key[i][11:0] ^ $random;
    end
end

// 定义SPN结构
wire [63:0] subkey[31:0];
assign subkey[0] = round_key[0][79:16];
for (int i = 1; i < 31; i = i + 1) begin
    assign subkey[i] = round_key[i][79:16] ^ (subkey[i-1] >> 8);
end
wire [63:0] state;
assign state = plaintext;
for (int i = 0; i < 31; i = i + 1) begin
    wire [63:0] round_key_i;
    assign round_key_i = subkey[i];
    wire [63:0] state_i;
    assign state_i = state;
    // Substitution 层
    for (int j = 0; j < 16; j = j + 1) begin
        wire [3:0] s_in;
        assign s_in = state_i[j*4+3:j*4];
        wire [3:0] s_out;
        assign s_out = S[s_in];
        state_i[j*4+3:j*4] = s_out;
    end
    // Permutation 层
    wire [63:0] permuted;
    assign permuted = {state_i[15:0], state_i[47:32], state_i[31:16], state_i[63:48]};
    // 使用随机掩码掩蔽
    permuted[11:0] = permuted[11:0] ^ $random;
    // XOR 层
    state = permuted ^ round_key_i;
end
assign ciphertext = state;

endmodule

在这个实现中，我们先定义了S盒和P盒，然后使用随机掩码生成31轮的轮密钥。接着，我们将S盒和P盒组合成SPN结构，并使用随机掩码掩蔽每一轮的加密操作。最后，我们将输入的明文和生成的轮密钥送入SPN结构中，得到密文输出。