#include <stdio.h>
#include <stdlib.h>
#include <math.h>
// Função para calcular o MDC (Máximo Divisor Comum)
int mdc(int a, int b) {
if (b == 0)
return a;
return mdc(b, a % b);
}
// Função para calcular o módulo inverso usando o algoritmo de Euclides estendido
int mod_inverse(int e, int phi) {
int x0 = 0, x1 = 1, temp, quotient;
int a = phi, b = e;
while (b > 0) {
quotient = a / b;
temp = x1;
x1 = x0 - quotient * x1;
x0 = temp;
temp = a;
a = b;
b = temp % b;
}
if (a == 1) {
if (x0 < 0) {
x0 += phi;
}
return x0;
}
return -1; // Não encontrou o inverso
}
// Função para calcular o módulo φ(n)
int calculate_phi(int p, int q) {
return (p - 1) * (q - 1);
}
// Função para gerar as chaves RSA (públicas e privadas)
void generate_keys(int p, int q, int e, int *n, int *d) {
*n = p * q;
int phi = calculate_phi(p, q);
*d = mod_inverse(e, phi);
if (*d == -1) {
printf("Erro ao encontrar o inverso modular.\n");
exit(1);
}
}
// Função para criptografar um caractere usando RSA
int encrypt(int char_value, int e, int n) {
long long int encrypted = 1;
for (int i = 0; i < e; i++) {
encrypted = (encrypted * char_value) % n;
}
return encrypted;
}
// Função para descriptografar um número usando RSA
int decrypt(int encrypted_value, int d, int n) {
long long int decrypted = 1;
for (int i = 0; i < d; i++) {
decrypted = (decrypted * encrypted_value) % n;
}
return decrypted;
}
int main() {
int p, q, e, n, d;
printf("Digite os valores primos p e q:\n");
scanf("%d %d", &p, &q);
printf("Digite o valor de E (número público):\n");
scanf("%d", &e);
n = p * q;
int phi = calculate_phi(p, q);
// Verifica se E é coprimo com φ(n)
if (mdc(e, phi) != 1) {
printf("O número E não é coprimo com φ(n).\n");
return 1;
}
generate_keys(p, q, e, &n, &d);
printf("Chave pública (n, e): (%d, %d)\n", n, e);
printf("Chave privada (n, d): (%d, %d)\n", n, d);
char mensagem[100];
printf("Digite a mensagem para criptografar:\n");
scanf("%s", mensagem);
printf("Mensagem criptografada:\n");
for (int i = 0; mensagem[i] != '\0'; i++) {
int char_value = mensagem[i] - 'A' + 11; // Conversão de A=11
int encrypted = encrypt(char_value, e, n);
printf("%d ", encrypted);
}
printf("\n");
// Descriptografar a mensagem
printf("Mensagem descriptografada:\n");
for (int i = 0; mensagem[i] != '\0'; i++) {
int encrypted = (int) (mensagem[i] - 'A' + 11); // Simulação dos valores criptografados
int decrypted = decrypt(encrypted, d, n);
char decrypted_char = (decrypted - 11) + 'A'; // Convertendo para o caractere original
printf("%c", decrypted_char);
}
printf("\n");
return 0;
}
Write, Run & Share C Language code online using OneCompiler's C online compiler for free. It's one of the robust, feature-rich online compilers for C language, running the latest C version which is C18. Getting started with the OneCompiler's C editor is really simple and pretty fast. The editor shows sample boilerplate code when you choose language as 'C' and start coding!
OneCompiler's C online editor supports stdin and users can give inputs to programs using the STDIN textbox under the I/O tab. Following is a sample C program which takes name as input and print your name with hello.
#include <stdio.h>
int main()
{
char name[50];
printf("Enter name:");
scanf("%s", name);
printf("Hello %s \n" , name );
return 0;
}
C language is one of the most popular general-purpose programming language developed by Dennis Ritchie at Bell laboratories for UNIX operating system. The initial release of C Language was in the year 1972. Most of the desktop operating systems are written in C Language.
When ever you want to perform a set of operations based on a condition if-else is used.
if(conditional-expression) {
// code
} else {
// code
}
You can also use if-else for nested Ifs and if-else-if ladder when multiple conditions are to be performed on a single variable.
Switch is an alternative to if-else-if ladder.
switch(conditional-expression) {
case value1:
// code
break; // optional
case value2:
// code
break; // optional
...
default:
// code to be executed when all the above cases are not matched;
}
For loop is used to iterate a set of statements based on a condition.
for(Initialization; Condition; Increment/decrement){
// code
}
While is also used to iterate a set of statements based on a condition. Usually while is preferred when number of iterations are not known in advance.
while(condition) {
// code
}
Do-while is also used to iterate a set of statements based on a condition. It is mostly used when you need to execute the statements atleast once.
do {
// code
} while (condition);
Array is a collection of similar data which is stored in continuous memory addresses. Array values can be fetched using index. Index starts from 0 to size-1.
data-type array-name[size];
data-type array-name[size][size];
Function is a sub-routine which contains set of statements. Usually functions are written when multiple calls are required to same set of statements which increases re-usuability and modularity.
Two types of functions are present in C
Library functions are the in-built functions which are declared in header files like printf(),scanf(),puts(),gets() etc.,
User defined functions are the ones which are written by the programmer based on the requirement.
return_type function_name(parameters);
function_name (parameters)
return_type function_name(parameters) {
//code
}