利用openssl库进行RSA加密

NSString *RSA_encrypt(NSString *data)
{
    unsigned char *str=(unsigned char*)[data UTF8String];  //把要加密的数据进行utf8编码
    unsigned char *p_en;
    RSA *p_rsa;
    int rsa_len;
    NSString *public = formatPublicKey(PUBLIC_KEY);     //把服务器的公钥格式化
    NSData *pub= [public dataUsingEncoding: NSUTF8StringEncoding];   //公钥utf8编码
    BIO *bio = BIO_new_mem_buf((void *)[pub bytes], (int)[pub length]);  //用bio函数把编码过的公钥写到内存中
    p_rsa = PEM_read_bio_RSA_PUBKEY(bio, NULL, 0, NULL);  //用pem格式读取内存中的公钥
    BIO_free(bio);  //内存中释放bio
    rsa_len=RSA_size(p_rsa);  //计算公钥的长度
    p_en=(unsigned char *)malloc(rsa_len+1);  //分配公钥长度的内存
    memset(p_en,0,rsa_len+1);  //内存清零
    int Result=RSA_public_encrypt((int)strlen((const char*)str),(unsigned char *)str,(unsigned char*)p_en,p_rsa,RSA_PKCS1_PADDING);
	//加密公钥  int RSA_public_encrypt(int flen, unsigned char *from, unsigned char *to, RSA ＊rsa, int padding);
    if(Result<0)
        return NULL;
    
    RSA_free(p_rsa);  //内存中释放p_rsa
    NSMutableString *result = [NSMutableString stringWithCapacity:128];  //创建一个128字符的可变字符串
    for(int i = 0; i < 128; i++)
        [result appendFormat:@"%02x", (unsigned char)p_en[i]];   //把加密的Result存储到result中去
    free(p_en);   //内存中释放p_en
    p_en=NULL;
    
    return result;
    
}