The simple encryption and decryption of
RSA in C language is not popular. It is available on the Internet. Now I use my experimental report to realize it: The
required data are:
two large prime numbers p,q;
n=p q;
t=(p -1) (q-1);
public key e satisfies (e, t)=1;
private key d satisfies de==1 (mod n);
encryption formula c=m^e(mod n), c is ciphertext , M is plaintext;
pay attention to plaintext m<n when encrypting;
Here is another code block:
//判断两个数是不是互素。
void gcd(int p,int q){
int temp1,temp2; //q=temp2*p+temp1 ;
if(q<p){
temp1=p;
p=q;
q=temp1;
}
temp1=q%p,temp2=q/p;
while(temp1!=0){
q=p;p=temp1;
temp1=q%p;temp2=q/p;
}
if(temp1==0&&temp2==q){
printf("符合条件！\n");
}
else{
printf("不符合条件！\n");
}
}
//求e关于模(p-1)(q-1)的逆元d：即私钥
int extend(int e,int t){
int d;
for(d=0;d<t;d++){
if(e*d%t==1)
return d;
}
}
In the encryption function, the symbolic plaintext must be converted into digital plaintext to encrypt. The encryption principle is to encrypt the ascii codes corresponding to each letter in turn; the encryption formula pow(m,e)%n in the encryption function may cause overflow, which is After the solution:
//加密函数
void encrypt(int e,int n){
//自己指定指数e
//先将符号明文转换成字母所对应的ascii码。
char mingwen[100]; //符号明文
printf("请输入明文：\n");
scanf("%s",mingwen); //gets(mingwen);
//gets(mingwen);
changdu=strlen(mingwen);
int ming[strlen(mingwen)]; //定义符号明文
for(int i=0;i<strlen(mingwen);i++){
ming[i]=mingwen[i]; //将字母转换成对应的ascii码。
printf("%d",mingwen[i]);
}
printf("\n");
//开始加密
printf("加密开始…………………………\n");
int zhuan=1; //c为加密后的数字密文
for(int i=0;i<strlen(mingwen);i++){
for(int j=0;j<e;j++){
zhuan=zhuan*ming[i]%n;
//zhuan=zhuan%n;
}
c[i]=zhuan;
//printf("%d",mi[i]);
zhuan=1;
}
printf("加密密文为：\n");
for(int i=0;i<strlen(mingwen);i++)
printf("%d",c[i]);
printf("\n加密结束…………………………\n");
}
Solve the previous: (as long as the calculation of the large power exponent is calculated separately)
//以下写法会导致溢出！
// {
// for(int i=0;i<strlen(mingwen);i++){
// zhuan=pow()
// mi[i]=int(pow(ming[i],e))%n;
// printf("密文为：%d",mi[0]);
// }
// }
// printf("密文为：\n");
// for(int i=0;i<strlen(mingwen);i++){
// printf("%d",mi[i]);
// }
//解密函数
void decrypto(int d,int n){
int de_mingwen[changdu],zhuan1=1;
char de_ming[changdu];
for(int i=0;i<changdu;i++){
for(int j=0;j<d;j++){
zhuan1=zhuan1*c[i]%n;
//zhuan=zhuan%n;
}
de_mingwen[i]=zhuan1;
//printf("%d",mi[i]);
zhuan1=1;
}
printf("解密开始…………………………\n");
printf("解密后的数字明文为：\n");
for(int i=0;i<changdu;i++)
printf("%d",de_mingwen[i]);
printf("\n");
printf("解密后的符号明文为：\n");
for(int i=0;i<changdu;i++){
de_ming[i]=de_mingwen[i];
printf("%c",de_ming[i]);
}
printf("\n解密结束…………………………\n");
}
Main function:
int main(){
int q,p,e,d,n,t,x;
printf("请输入p:",p);scanf("%d",&p);
printf("请输入q:",q);scanf("%d",&q);
n=q*p;
t=(q-1)*(p-1);
gcd(p,q);
printf("请输入一个指数e，使得（e,t）=1：");scanf("%d",&e);
gcd(e,t);
d=extend(e,t);
printf("密钥为：%d,一定保管好！",d);
printf("\n\n~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\n");
encrypt(e,n);
printf("\n请输入正确的密钥，密钥正确将解密上面的密文:");scanf("%d",&d);
decrypto(d,n);
printf("\n~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\n");
return 0;
}
Encryption function encrypt() cannot use gets() to input plaintext, because gets() will end when it encounters a carriage return, so that a single function test is no problem, but if the entire program is tested, it will end before the function is executed. Situation:
Replace with scanf("%s",mingwen), so it can be executed!
Remember to add the complete header file! Because I defined some global variables:
#include<stdio.h>
#include<string.h>
int changdu;
int c[100];
Xiaobai definitely understands the series! Because I'm also a good cook, I will write in more detail to prevent me from not knowing what it is next time I read it hahaha.
This is how the whole experiment is. It may be a bit rush to write, the whole program still has some delays, and some functions need to be optimized, but the basic functions are realized!
Here is a question I would like to ask predecessors:
how to use pointers in a function to access the variables of another function? In addition to using global variables, I hope that the predecessors will give an example, such as accessing the encrypted plaintext c in the encryption function in the decryption function.
There is an additional problem: how does a function return an array?