testing

rsa-algorithms/README.md

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+# rsa-algorithms Project
+
+This is a C project generated with the setup tool.

rsa-algorithms/build/Makefile

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+# Variables
+CC = gcc
+CFLAGS = -I../include -Wall -Wextra
+OBJDIR = ../obj
+SRCDIR = ../src
+BINDIR = ../build
+
+# Source files
+SOURCES = $(SRCDIR)/main.c $(SRCDIR)/rsa.c
+OBJECTS = $(OBJDIR)/main.o $(OBJDIR)/rsa.o
+
+# Build target
+TARGET = rsa
+
+# Rules
+all: $(BINDIR)/$(TARGET)
+
+$(BINDIR)/$(TARGET): $(OBJECTS)
+	$(CC) $(OBJECTS) -o $(BINDIR)/$(TARGET)
+
+$(OBJDIR)/%.o: $(SRCDIR)/%.c
+	$(CC) $(CFLAGS) -c $< -o $@
+
+clean:
+	rm -f $(OBJDIR)/*.o $(BINDIR)/$(TARGET)
+
+.PHONY: all clean
+

rsa-algorithms/include/rsa.h

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+#ifndef RSA_H
+#define RSA_H
+
+void rsa_generate_keys(unsigned long *e, unsigned long *d, unsigned long *n);
+unsigned long rsa_encrypt(unsigned long message, unsigned long e, unsigned long n);
+unsigned long rsa_decrypt(unsigned long ciphertext, unsigned long d, unsigned long n);
+
+#endif // RSA_H

rsa-algorithms/src/main.c

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+#include "rsa.h"
+#include <stdio.h>
+
+int main() {
+    unsigned long e, d, n;
+
+    // Generate public and private keys
+    rsa_generate_keys(&e, &d, &n);
+    printf("Public Key: (e = %lu, n = %lu)\n", e, n);
+    printf("Private Key: (d = %lu, n = %lu)\n", d, n);
+
+    // Ask for a message to encrypt (assuming it's an integer for simplicity)
+    unsigned long message;
+    printf("Enter a message to encrypt (as an integer smaller than %lu): ", n);
+    scanf("%lu", &message);
+
+    // Ensure message is smaller than n
+    if (message >= n) {
+        printf("Error: Message must be smaller than %lu.\n", n);
+        return 1;
+    }
+
+    // Encrypt the message
+    unsigned long ciphertext = rsa_encrypt(message, e, n);
+    printf("Encrypted message: %lu\n", ciphertext);
+
+    // Decrypt the message
+    unsigned long decrypted_message = rsa_decrypt(ciphertext, d, n);
+    printf("Decrypted message: %lu\n", decrypted_message);
+
+    return 0;
+}
+

rsa-algorithms/src/rsa.c

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+#include "rsa.h"
+#include <stdio.h>
+#include <stdlib.h>
+#include <time.h>
+
+// Helper function to calculate the greatest common divisor (GCD)
+static unsigned long gcd(unsigned long a, unsigned long b) {
+    while (b != 0) {
+        unsigned long temp = b;
+        b = a % b;
+        a = temp;
+    }
+    return a;
+}
+
+// Helper function to find the modular inverse using the extended Euclidean algorithm
+static unsigned long mod_inverse(unsigned long e, unsigned long phi) {
+    long t = 0, newt = 1;
+    unsigned long r = phi, newr = e;
+    
+    while (newr != 0) {
+        unsigned long quotient = r / newr;
+
+        // Update t and newt
+        long temp = t;
+        t = newt;
+        newt = temp - quotient * newt;
+
+        // Update r and newr
+        unsigned long temp_r = r;
+        r = newr;
+        newr = temp_r - quotient * newr;
+    }
+
+    if (r > 1) return 0;  // e is not invertible
+    if (t < 0) t += phi;  // Ensure t is positive
+    
+    return (unsigned long)t;
+}
+
+
+// Generate RSA keys (public and private)
+void rsa_generate_keys(unsigned long *e, unsigned long *d, unsigned long *n) {
+    // Two prime numbers (for simplicity, using small values)
+    unsigned long p = 61, q = 53;
+    *n = p * q;
+    unsigned long phi = (p - 1) * (q - 1);
+
+    // Choose e such that 1 < e < phi(n) and gcd(e, phi(n)) = 1
+    *e = 17;  // Commonly chosen small prime number
+    if (gcd(*e, phi) != 1) {
+        printf("Error: e and phi(n) are not coprime.\n");
+        exit(1);
+    }
+
+    // Calculate d, the modular inverse of e mod phi(n)
+    *d = mod_inverse(*e, phi);
+    if (*d == 0) {
+        printf("Error: Could not find modular inverse of e.\n");
+        exit(1);
+    }
+}
+
+// Encrypt message using public key (e, n)
+unsigned long rsa_encrypt(unsigned long message, unsigned long e, unsigned long n) {
+    unsigned long result = 1;
+    for (unsigned long i = 0; i < e; i++) {
+        result = (result * message) % n;
+    }
+    return result;
+}
+
+// Decrypt ciphertext using private key (d, n)
+unsigned long rsa_decrypt(unsigned long ciphertext, unsigned long d, unsigned long n) {
+    unsigned long result = 1;
+    for (unsigned long i = 0; i < d; i++) {
+        result = (result * ciphertext) % n;
+    }
+    return result;
+}
+