ex1

tp2/spn.c

@@ -0,0 +1,86 @@
+#include "spn.h"
+
+unsigned char do_subst(unsigned char w, unsigned char subst[16]) {
+    return subst[w];
+}
+
+unsigned char do_perm(unsigned char w, unsigned char perm[16]) {
+    unsigned char result = 0;
+    for (int i = 0; i < 8; i++) {
+        if ((w >> i) & 1)
+            result |= (1 << perm[i]);
+    }
+    return result;
+}
+
+unsigned short apply_perm16(unsigned short w, unsigned char perm[16]) {
+    unsigned short result = 0;
+    for (int i = 0; i < 16; i++) {
+        if ((w >> i) & 1)
+            result |= (1 << perm[i]);
+    }
+    return result;
+}
+
+unsigned short apply_subst16(unsigned short w, unsigned char subst[16]) {
+    unsigned short result = 0;
+    for (int i = 0; i < 4; i++) {
+        unsigned char nibble = (w >> (i * 4)) & 0xF;
+        result |= (do_subst(nibble, subst) << (i * 4));
+    }
+    return result;
+}
+
+unsigned short encrypt(
+    unsigned short w,
+    unsigned int key,
+    unsigned char perm[16],
+    unsigned char subst[16]
+) {
+    for (int round = 0; round < 2; round++) {
+        unsigned char round_key = (key >> (8 * (3 - round))) & 0xFF;
+        w ^= (round_key << 8) | round_key;
+
+        w = apply_subst16(w, subst);
+        w = apply_perm16(w, perm);
+    }
+
+    // Dernier round - pas de permutation
+    unsigned char round_key = (key & 0xFF);
+    w ^= (round_key << 8) | round_key;
+    w = apply_subst16(w, subst);
+
+    return w;
+}
+
+unsigned short decrypt(
+    unsigned short w,
+    unsigned int key,
+    unsigned char perm[16],
+    unsigned char subst[16]
+) {
+    // Inverser la substitution
+    unsigned char inv_subst[16];
+    for (int i = 0; i < 16; i++)
+        inv_subst[subst[i]] = i;
+
+    // Inverser la permutation
+    unsigned char inv_perm[16];
+    for (int i = 0; i < 16; i++)
+        inv_perm[perm[i]] = i;
+
+    // Dernier tour
+    w = apply_subst16(w, inv_subst);
+    unsigned char round_key = (key & 0xFF);
+    w ^= (round_key << 8) | round_key;
+
+    // 2 tours inverses
+    for (int round = 1; round >= 0; round--) {
+        w = apply_perm16(w, inv_perm);
+        w = apply_subst16(w, inv_subst);
+        round_key = (key >> (8 * (3 - round))) & 0xFF;
+        w ^= (round_key << 8) | round_key;
+    }
+
+    return w;
+}

tp2/spn.h

@@ -0,0 +1,21 @@
+#ifndef _SPN_H
+#define _SPN_H
+
+unsigned char do_perm(unsigned char w, unsigned char perm[16]);
+unsigned char do_subst(unsigned char w, unsigned char subst[16]);
+
+unsigned short encrypt(
+    unsigned short w,
+    unsigned int key,
+    unsigned char perm[16],
+    unsigned char subst[16]
+);
+
+unsigned short decrypt(
+    unsigned short w,
+    unsigned int key,
+    unsigned char perm[16],
+    unsigned char subst[16]
+);
+
+#endif