#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
// Função para calcular o máximo divisor comum (MDC)
int mdc(int a, int b) {
while (b != 0) {
int temp = b;
b = a % b;
a = temp;
}
return a;
}
// Função para calcular a potência modular (base^exp % mod)
long long potencia_modular(long long base, long long exp, long long mod) {
long long resultado = 1;
base = base % mod;
while (exp > 0) {
if (exp % 2 == 1) {
resultado = (resultado * base) % mod;
}
exp = exp >> 1;
base = (base * base) % mod;
}
return resultado;
}
// Função para codificar uma string em números com base no pré-código
void codificar_texto(const char *texto, int *codigo, int tamanho_bloco) {
for (int i = 0; i < strlen(texto); i++) {
if (texto[i] >= 'A' && texto[i] <= 'Z') {
codigo[i] = 11 + (texto[i] - 'A');
} else if (texto[i] == ' ') {
codigo[i] = 10; // Espaço = 10
} else {
codigo[i] = 0; // Caracteres desconhecidos
}
}
}
// Função para calcular o inverso modular de e em relação a φ(n)
int inverso_modular(int e, int phi) {
int t = 0, new_t = 1, r = phi, new_r = e;
while (new_r != 0) {
int quociente = r / new_r;
int temp = new_t;
new_t = t - quociente * new_t;
t = temp;
temp = new_r;
new_r = r - quociente * new_r;
r = temp;
}
if (r > 1) return -1; // Não existe inverso modular
if (t < 0) t += phi;
return t;
}
int main() {
// Variáveis para os números primos e o expoente público
int p, q, e, tamanho_bloco;
printf("Digite os numeros primos p e q: ");
scanf("%d %d", &p, &q);
printf("Digite o numero E (expoente publico): ");
scanf("%d", &e);
printf("Digite o tamanho do bloco: ");
scanf("%d", &tamanho_bloco);
// Calcula n, z (φ(n)) e verifica se e é válido
int n = p * q;
int phi = (p - 1) * (q - 1);
if (mdc(e, phi) != 1) {
printf("O numero E não e' coprimo com φ(n). Tente novamente.\n");
return 1;
}
// Calcula o expoente privado d
int d = inverso_modular(e, phi);
if (d == -1) {
printf("Nao foi possível calcular o inverso modular.\n");
return 1;
}
printf("Chave publica: (n = %d, e = %d)\n", n, e);
printf("Chave privada: (n = %d, d = %d)\n", n, d);
// Entrada de texto para codificação
char texto[256];
printf("Digite o texto para criptografar (A-Z e espaço): ");
getchar(); // Limpa o buffer
fgets(texto, 256, stdin);
texto[strcspn(texto, "\n")] = '\0'; // Remove o \n do final
// Codifica o texto
int codigo[256] = {0};
codificar_texto(texto, codigo, tamanho_bloco);
printf("\nTexto codificado: ");
for (int i = 0; i < strlen(texto); i++) {
printf("%d ", codigo[i]);
}
// Criptografia RSA
printf("\nTexto criptografado: ");
for (int i = 0; i < strlen(texto); i++) {
long long cifra = potencia_modular(codigo[i], e, n);
printf("%lld ", cifra);
}
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
}