利用feistal算法和RSA算法，以数字信封的形式对明文文件进行加密。要求如下： 1、发送方利用系统自带的伪随机数生成函数生成会话密钥 2、用接收方的公钥对会话密钥加密 3、用会话密钥以OFB的模式对明文文件p_text.txt（文件大于1KB）进行加密，结果存于密文文件c_text.txt 4、接收方利用私钥解密会话密钥，然后用会话密钥对密文文件解密，结果存于明文文件p1_text.txt，最后对比p_text.txt和p1_text.txt

以下是C语言实现示例：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <openssl/rsa.h>
#include <openssl/pem.h>
#include <openssl/rand.h>
#include <openssl/evp.h>

#define BLOCK_SIZE 8 // Feistal算法分块大小
#define KEY_SIZE 128 // RSA算法密钥长度

// 生成随机数
void generate_random(unsigned char *key, int len) {
    int i;
    srand((unsigned int)time(NULL));
    for (i = 0; i < len; i++) {
        key[i] = rand() % 256;
    }
}

// Feistal算法的轮函数
void feistal_round(unsigned char *data, unsigned char *key) {
    int i;
    unsigned char tmp[BLOCK_SIZE];
    memcpy(tmp, data, BLOCK_SIZE); // 保存data的副本
    for (i = 0; i < BLOCK_SIZE; i++) {
        data[i] ^= key[i]; // 异或操作
    }
    memcpy(key, tmp, BLOCK_SIZE); // 更新key
}

// Feistal算法加密
void feistal_encrypt(unsigned char *data, unsigned char *key, int rounds) {
    int i;
    for (i = 0; i < rounds; i++) {
        feistal_round(data, key);
    }
}

// RSA加密
int rsa_encrypt(unsigned char *in, int in_len, unsigned char *out, RSA *rsa) {
    int len = RSA_public_encrypt(in_len, in, out, rsa, RSA_PKCS1_PADDING);
    return len;
}

// RSA解密
int rsa_decrypt(unsigned char *in, int in_len, unsigned char *out, RSA *rsa) {
    int len = RSA_private_decrypt(in_len, in, out, rsa, RSA_PKCS1_PADDING);
    return len;
}

// OFB模式加密
void ofb_encrypt(FILE *in, FILE *out, unsigned char *key, int key_len) {
    unsigned char iv[BLOCK_SIZE], tmp[BLOCK_SIZE], cipher[BLOCK_SIZE];
    int i, nread;
    EVP_CIPHER_CTX *ctx = EVP_CIPHER_CTX_new();
    EVP_EncryptInit_ex(ctx, EVP_aes_128_ofb(), NULL, key, iv);
    memcpy(tmp, iv, BLOCK_SIZE);
    while ((nread = fread(tmp, 1, BLOCK_SIZE, in)) > 0) {
        EVP_EncryptUpdate(ctx, cipher, &i, tmp, BLOCK_SIZE);
        fwrite(cipher, 1, nread, out);
        memcpy(tmp, cipher, BLOCK_SIZE);
    }
    EVP_EncryptFinal_ex(ctx, cipher, &i);
    fwrite(cipher, 1, i, out);
    EVP_CIPHER_CTX_free(ctx);
}

// OFB模式解密
void ofb_decrypt(FILE *in, FILE *out, unsigned char *key, int key_len) {
    unsigned char iv[BLOCK_SIZE], tmp[BLOCK_SIZE], cipher[BLOCK_SIZE];
    int i, nread;
    EVP_CIPHER_CTX *ctx = EVP_CIPHER_CTX_new();
    EVP_DecryptInit_ex(ctx, EVP_aes_128_ofb(), NULL, key, iv);
    memcpy(tmp, iv, BLOCK_SIZE);
    while ((nread = fread(tmp, 1, BLOCK_SIZE, in)) > 0) {
        EVP_DecryptUpdate(ctx, cipher, &i, tmp, BLOCK_SIZE);
        fwrite(cipher, 1, nread, out);
        memcpy(tmp, cipher, BLOCK_SIZE);
    }
    EVP_DecryptFinal_ex(ctx, cipher, &i);
    fwrite(cipher, 1, i, out);
    EVP_CIPHER_CTX_free(ctx);
}

int main() {
    unsigned char key[BLOCK_SIZE], iv[BLOCK_SIZE];
    unsigned char enc_key[KEY_SIZE], dec_key[KEY_SIZE];
    unsigned char buffer[BLOCK_SIZE];
    int i, nread;
    FILE *in, *out;
    RSA *rsa;
    EVP_PKEY *pubkey, *prikey;
    char *pubkey_path = "pubkey.pem";
    char *prikey_path = "prikey.pem";
    char *p_text_path = "p_text.txt";
    char *c_text_path = "c_text.txt";
    char *p1_text_path = "p1_text.txt";
    int feistal_rounds = 16;

    // 读取明文文件
    in = fopen(p_text_path, "rb");
    if (in == NULL) {
        printf("Failed to open file %s\n", p_text_path);
        return 1;
    }

    // 生成Feistal算法的轮密钥
    generate_random(key, BLOCK_SIZE);
    memcpy(iv, key, BLOCK_SIZE);

    // 生成会话密钥
    generate_random(enc_key, KEY_SIZE / 8);

    // 用接收方的公钥加密会话密钥
    pubkey = EVP_PKEY_new();
    FILE *pubkey_file = fopen(pubkey_path, "r");
    if (!PEM_read_PUBKEY(pubkey_file, &pubkey, NULL, NULL)) {
        printf("Failed to read public key\n");
        return 1;
    }
    fclose(pubkey_file);
    rsa = EVP_PKEY_get1_RSA(pubkey);
    int enc_len = rsa_encrypt(enc_key, KEY_SIZE / 8, enc_key, rsa);

    // 将加密后的会话密钥和Feistal算法的轮密钥写入密文文件
    out = fopen(c_text_path, "wb");
    fwrite(enc_key, 1, enc_len, out);
    fwrite(key, 1, BLOCK_SIZE, out);

    // 使用OFB模式加密明文文件
    ofb_encrypt(in, out, iv, BLOCK_SIZE);
    fclose(out);
    fclose(in);

    // 读取密文文件
    in = fopen(c_text_path, "rb");
    if (in == NULL) {
        printf("Failed to open file %s\n", c_text_path);
        return 1;
    }

    // 解密会话密钥
    prikey = EVP_PKEY_new();
    FILE *prikey_file = fopen(prikey_path, "r");
    if (!PEM_read_PrivateKey(prikey_file, &prikey, NULL, NULL)) {
        printf("Failed to read private key\n");
        return 1;
    }
    fclose(prikey_file);
    rsa = EVP_PKEY_get1_RSA(prikey);
    int dec_len = rsa_decrypt(enc_key, enc_len, dec_key, rsa);

    // 读取Feistal算法的轮密钥
    nread = fread(buffer, 1, BLOCK_SIZE, in);
    memcpy(key, buffer, BLOCK_SIZE);

    // 使用OFB模式解密密文文件
    out = fopen(p1_text_path, "wb");
    ofb_decrypt(in, out, iv, BLOCK_SIZE);
    fclose(out);
    fclose(in);

    // 比较明文和解密后的明文是否相同
    in = fopen(p_text_path, "rb");
    out = fopen(p1_text_path, "rb");
    while ((nread = fread(buffer, 1, BLOCK_SIZE, in)) > 0) {
        fread(iv, 1, BLOCK_SIZE, out);
        feistal_encrypt(iv, key, feistal_rounds);
        for (i = 0; i < nread; i++) {
            buffer[i] ^= iv[i];
        }
        fwrite(buffer, 1, nread, out);
    }
    fclose(in);
    fclose(out);

    printf("Encryption and decryption completed successfully.\n");
    return 0;
}

需要注意的是，这段代码中使用了OpenSSL库来实现RSA加密和解密、OFB模式加密和解密等操作，需要在编译时链接该库。在gcc编译时可以添加`-lcrypto`选项。此外，还需要自行生成公钥和私钥文件，并将其分别命名为`pubkey.pem`和`prikey.pem`，并放在代码所在目录下。