ajout crypto

crypto/TP2/spn_decrypt_file.c

@@ -0,0 +1,41 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include "spn.h"
+
+void decrypt_file(const char *input_filename, const char *output_filename, unsigned short key, unsigned char perm[8], unsigned char subst[16]) {
+    FILE *in = fopen(input_filename, "rb");
+    FILE *out = fopen(output_filename, "wb");
+    if (!in || !out) {
+        perror("Erreur ouverture fichier");
+        exit(EXIT_FAILURE);
+    }
+
+    unsigned char byte;
+    while (fread(&byte, 1, 1, in) == 1) {
+        unsigned char decrypted = decrypt(byte, key, perm, subst);
+        fwrite(&decrypted, 1, 1, out);
+    }
+
+    fclose(in);
+    fclose(out);
+}
+
+int main(int argc, char *argv[]) {
+    if (argc != 6) {
+        printf("Usage: %s clé.txt subst.txt perm.txt fichier_chiffre fichier_déchiffré\n", argv[0]);
+        return EXIT_FAILURE;
+    }
+
+    unsigned short key;
+    unsigned char subst[16];
+    unsigned char perm[8];
+
+    read_key(argv[1], &key);
+    read_subst(argv[2], subst);
+    read_perm(argv[3], perm);
+
+    decrypt_file(argv[4], argv[5], key, perm, subst);
+
+    printf("Déchiffrement terminé : %s → %s\n", argv[4], argv[5]);
+    return EXIT_SUCCESS;
+}