Squashed 'external/toxcore/c-toxcore/' content from commit 67badf69

git-subtree-dir: external/toxcore/c-toxcore
git-subtree-split: 67badf69416a74e74f6d7eb51dd96f37282b8455

other/fun/cracker_simple.c

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+/* Public key cracker.
+ *
+ * Can be used to find public keys starting with specific hex (ABCD) for example.
+ *
+ * NOTE: There's probably a way to make this faster.
+ *
+ * Usage: ./cracker ABCDEF
+ *
+ * Will try to find a public key starting with: ABCDEF
+ */
+
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+
+/* Sodium includes*/
+#include <sodium/crypto_scalarmult_curve25519.h>
+#include <sodium/randombytes.h>
+
+#include "../../testing/misc_tools.h"
+#include "../../toxcore/ccompat.h"
+
+// Secret key and public key length
+#define KEY_LEN 32
+
+static void print_key(const uint8_t *client_id)
+{
+    for (int j = 0; j < KEY_LEN; ++j) {
+        printf("%02X", client_id[j]);
+    }
+}
+
+
+int main(int argc, char *argv[])
+{
+    if (argc < 2) {
+        printf("usage: ./cracker public_key(or beginning of one in hex format)\n");
+        return 0;
+    }
+
+    long long unsigned int num_tries = 0;
+
+    size_t len = strlen(argv[1]) / 2;
+    unsigned char *key = hex_string_to_bin(argv[1]);
+    uint8_t pub_key[KEY_LEN], priv_key[KEY_LEN], c_key[KEY_LEN];
+
+    if (len > KEY_LEN) {
+        printf("%zu characters given, truncating to: %d\n", len * 2, KEY_LEN * 2);
+        len = KEY_LEN;
+    }
+
+    memcpy(c_key, key, len);
+    free(key);
+    randombytes(priv_key, KEY_LEN);
+
+    while (1) {
+        crypto_scalarmult_curve25519_base(pub_key, priv_key);
+
+        if (memcmp(c_key, pub_key, len) == 0) {
+            break;
+        }
+
+        /*
+         * We can't use the first and last bytes because they are masked in
+         * curve25519. Using them would generate duplicate keys.
+         */
+        for (int i = (KEY_LEN - 1); i > 1; --i) {
+            priv_key[i - 1] += 1;
+
+            if (priv_key[i - 1] != 0) {
+                break;
+            }
+        }
+
+        ++num_tries;
+    }
+
+    printf("Public key:\n");
+    print_key(pub_key);
+    printf("\nPrivate key:\n");
+    print_key(priv_key);
+    printf("\n %llu keys tried\n", num_tries);
+    return 0;
+}