tp1

tp1/ex2/xtea.c

@@ -0,0 +1,83 @@
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define DELTA 0x9E3779B9
+
+void xtea_encrypt_block(uint32_t *v, const uint32_t key[4]) {
+    uint32_t v0 = v[0], v1 = v[1], sum = 0;
+    for (unsigned i = 0; i < 32; i++) {
+        v0 += (((v1 << 4) ^ (v1 >> 5)) + v1) ^ (sum + key[sum & 3]);
+        sum += DELTA;
+        v1 += (((v0 << 4) ^ (v0 >> 5)) + v0) ^ (sum + key[(sum >> 11) & 3]);
+    }
+    v[0] = v0;
+    v[1] = v1;
+}
+
+void xtea_decrypt_block(uint32_t *v, const uint32_t key[4]) {
+    uint32_t v0 = v[0], v1 = v[1];
+    uint32_t sum = DELTA * 32;
+    for (unsigned i = 0; i < 32; i++) {
+        v1 -= (((v0 << 4) ^ (v0 >> 5)) + v0) ^ (sum + key[(sum >> 11) & 3]);
+        sum -= DELTA;
+        v0 -= (((v1 << 4) ^ (v1 >> 5)) + v1) ^ (sum + key[sum & 3]);
+    }
+    v[0] = v0;
+    v[1] = v1;
+}
+
+void xtea_process(int encrypt, const char *keyfile, const char *infile, const char *outfile) {
+    uint32_t key[4];
+
+    FILE *fk = fopen(keyfile, "rb");
+    if (!fk || fread(key, sizeof *key, 4, fk) != 4) {
+        fprintf(stderr, "Erreur lecture clé\n");
+        exit(1);
+    }
+    fclose(fk);
+
+    FILE *fin  = fopen(infile,  "rb");
+    FILE *fout = fopen(outfile, "wb");
+    if (!fin || !fout) {
+        fprintf(stderr, "Erreur ouverture fichiers\n");
+        exit(1);
+    }
+
+    uint8_t block[8];
+    size_t  n;
+
+    while ((n = fread(block, 1, 8, fin)) == 8) {
+        xtea_encrypt_block((uint32_t*)block, key);
+        if (!encrypt)
+            xtea_decrypt_block((uint32_t*)block, key);
+        fwrite(block, 1, 8, fout);
+    }
+
+    if (encrypt) {
+        for (size_t i = n; i < 8 - 1; i++) {
+            block[i] = 0;
+        }
+        block[8 - 1] = 8 - n;
+        xtea_encrypt_block((uint32_t*)block, key);
+        fwrite(block, 1, 8, fout);
+    } else if (n > 0) {
+        fprintf(stderr, "Erreur : fichier chiffré mal aligné\n");
+        exit(1);
+    }
+
+    fclose(fin);
+    fclose(fout);
+}
+
+int main(int argc, char *argv[])
+{
+    if (argc != 5) {
+        fprintf(stderr, "Usage : %s -e|-d keyfile infile outfile\n", argv[0]);
+        return 1;
+    }
+    int enc = (strcmp(argv[1], "-e") == 0);
+    xtea_process(enc, argv[2], argv[3], argv[4]);
+    return 0;
+}