CLI: use one process to test many keys for mfkey32v2

It is done by adding a "server" mode (on STDIN/STDOUT) to `mfkey32v2`
using `--server`.

This improves the speed of the decrypt process, as it prevents a lot
of Python calls to `subprocess.Popen()` (and of course, a lot of
fork/execve syscalls).

On my laptop, with the same logs (37 records for one block and 37
records for another block), here are the performances, as measuerd
using a simple command:

```bash
time echo -e "hw connect\nhf mf elog --decrypt\nhw disconnect" | ./chameleon_cli_main.py
```

|                           |         | real       | user       | sys       |
|---------------------------|---------|------------|------------|-----------|
| Before parallelisation    | 05ea03d | 14m59,277s | 14m47,995s | 0m8,490s  |
| With parallelisation      | RfidResearchGroup#187    | 6m13,513s  | 35m2,926s  | 0m22,038s |
| With item skipping        | RfidResearchGroup#189    | 2m42,491s  | 15m43,425s | 0m9,881s  |
| With `mfkey32v2 --server` | this PR | 1m55,160s  | 0m1,315s   | 0m0,250s  |

CHANGELOG.md

@@ -3,6 +3,7 @@ All notable changes to this project will be documented in this file.
 This project uses the changelog in accordance with [keepchangelog](http://keepachangelog.com/). Please use this to write notable changes, which is not the same as git commit log...
 
 ## [unreleased][unreleased]
+ - Implement a "server" mode in mfkey32v2 to avoid spawning one process per combination (@p-l-)
  - Added command to check keys of multiple sectors at once (@taichunmin)
  - Fixed unused target key type parameter for nested (@petepriority)
  - Skip already used items `hf mf elog --decrypt` (@p-l-)

software/script/chameleon_cli_unit.py

@@ -1217,26 +1217,39 @@ def res_value(self, src_blk, src_type, src_key, dst_blk, dst_type, dst_key):
 _KEY = re.compile("[a-fA-F0-9]{12}", flags=re.MULTILINE)
 
 
+class Mfkey32v2Runner:
+
+    def __init__(self):
+        self.proc = subprocess.Popen(
+            [default_cwd / (f"mfkey32v2{'.exe' if sys.platform == 'win32' else ''}"), "--server"],
+            stdin=subprocess.PIPE,
+            stdout=subprocess.PIPE,
+            bufsize=1,
+            encoding="ascii",
+        )
+
+    def close(self):
+        self.proc.stdin.close()
+        self.proc.wait()
+
+    def check(self, items):
+        if not items:
+            self.close()
+            return None
+        self.proc.stdin.write(f"{items[0]['uid']} {items[0]['nt']} {items[0]['nr']} {items[0]['ar']} {items[1]['nt']} {items[1]['nr']} {items[1]['ar']}\n")
+        answer = self.proc.stdout.readline().strip()
+        if answer:
+            return answer, items
+        return None
+
+
+def _init_mfkey32v2_run():
+    global _MFKEY32V2_RUNNER
+    _MFKEY32V2_RUNNER = Mfkey32v2Runner()
+
+
 def _run_mfkey32v2(items):
-    output_str = subprocess.run(
-        [
-            default_cwd / ("mfkey32v2.exe" if sys.platform == "win32" else "mfkey32v2"),
-            items[0]["uid"],
-            items[0]["nt"],
-            items[0]["nr"],
-            items[0]["ar"],
-            items[1]["nt"],
-            items[1]["nr"],
-            items[1]["ar"],
-        ],
-        capture_output=True,
-        check=True,
-        encoding="ascii",
-    ).stdout
-    sea_obj = _KEY.search(output_str)
-    if sea_obj is not None:
-        return sea_obj[0], items
-    return None
+    return _MFKEY32V2_RUNNER.check(items)
 
 
 class ItemGenerator:
@@ -1308,13 +1321,17 @@ def decrypt_by_list(self, rs: list):
         msg3 = " key(s) found"
         n = 1
         gen = ItemGenerator(rs)
-        with Pool(cpu_count()) as pool:
+        with Pool(
+            processes=cpu_count(),
+            initializer=_init_mfkey32v2_run,
+        ) as pool:
             for result in pool.imap(_run_mfkey32v2, gen):
                 # TODO: if some keys already recovered, test them on item before running mfkey32 on item
                 if result is not None:
                     gen.key_found(*result)
                 print(f"{msg1}{n}{msg2}{len(gen.keys)}{msg3}\r", end="")
                 n += 1
+            pool.imap(_run_mfkey32v2, [[]] * cpu_count())
         print()
         return gen.keys
 

software/src/mfkey32v2.c

@@ -3,61 +3,41 @@
 #include <stdbool.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
 #include "crapto1.h"
 
-int main(int argc, char *argv[]) {
+void attack(
+    uint32_t uid,     // serial number
+    uint32_t nt0,     // tag challenge first
+    uint32_t nr0_enc, // first encrypted reader challenge
+    uint32_t ar0_enc, // first encrypted reader response
+    uint32_t nt1,     // tag challenge second
+    uint32_t nr1_enc, // second encrypted reader challenge
+    uint32_t ar1_enc, // second encrypted reader response
+    bool verbose
+) {
     struct Crypto1State *s, *t;
     uint64_t key;     // recovered key
-    uint32_t uid;     // serial number
-    uint32_t nt0;      // tag challenge first
-    uint32_t nt1;      // tag challenge second
-    uint32_t nr0_enc; // first encrypted reader challenge
-    uint32_t ar0_enc; // first encrypted reader response
-    uint32_t nr1_enc; // second encrypted reader challenge
-    uint32_t ar1_enc; // second encrypted reader response
     uint32_t ks2;     // keystream used to encrypt reader response
-
-    printf("MIFARE Classic key recovery - based 32 bits of keystream  VERSION2\n");
-    printf("Recover key from two 32-bit reader authentication answers only\n");
-    printf("This version implements Moebius two different nonce solution (like the supercard)\n\n");
-
-    if (argc < 8) {
-        printf("syntax: %s <uid> <nt> <nr_0> <ar_0> <nt1> <nr_1> <ar_1>\n\n", argv[0]);
-        return 1;
-    }
-
-    sscanf(argv[1], "%x", &uid);
-    sscanf(argv[2], "%x", &nt0);
-    sscanf(argv[3], "%x", &nr0_enc);
-    sscanf(argv[4], "%x", &ar0_enc);
-    sscanf(argv[5], "%x", &nt1);
-    sscanf(argv[6], "%x", &nr1_enc);
-    sscanf(argv[7], "%x", &ar1_enc);
-
-    printf("Recovering key for:\n");
-    printf("    uid: %08x\n", uid);
-    printf("   nt_0: %08x\n", nt0);
-    printf(" {nr_0}: %08x\n", nr0_enc);
-    printf(" {ar_0}: %08x\n", ar0_enc);
-    printf("   nt_1: %08x\n", nt1);
-    printf(" {nr_1}: %08x\n", nr1_enc);
-    printf(" {ar_1}: %08x\n", ar1_enc);
-
     // Generate lfsr successors of the tag challenge
-    printf("\nLFSR successors of the tag challenge:\n");
+    if (verbose) {
+      printf("\nLFSR successors of the tag challenge:\n");
+    }
     uint32_t p64 = prng_successor(nt0, 64);
     uint32_t p64b = prng_successor(nt1, 64);
-
-    printf("  nt': %08x\n", p64);
-    printf(" nt'': %08x\n", prng_successor(p64, 32));
+    if (verbose) {
+        printf("  nt': %08x\n", p64);
+        printf(" nt'': %08x\n", prng_successor(p64, 32));
+	printf("\nKeystream used to generate {ar} and {at}:\n");
+    }
+    bool found = false;
 
     // Extract the keystream from the messages
-    printf("\nKeystream used to generate {ar} and {at}:\n");
     ks2 = ar0_enc ^ p64;
-    printf("  ks2: %08x\n", ks2);
-
+    if (verbose) {
+        printf("  ks2: %08x\n", ks2);
+    }
     s = lfsr_recovery32(ar0_enc ^ p64, 0);
-
     for (t = s; t->odd | t->even; ++t) {
         lfsr_rollback_word(t, 0, 0);
         lfsr_rollback_word(t, nr0_enc, 1);
@@ -67,10 +47,77 @@ int main(int argc, char *argv[]) {
         crypto1_word(t, uid ^ nt1, 0);
         crypto1_word(t, nr1_enc, 1);
         if (ar1_enc == (crypto1_word(t, 0, 0) ^ p64b)) {
-            printf("\nFound Key: [%012" PRIx64 "]\n\n", key);
+            if (verbose) {
+                printf("\nFound Key: [%012" PRIx64 "]\n\n", key);
+	    }
+	    else {
+               printf("%012" PRIx64 "\n", key);
+	    }
+	    found = true;
             break;
         }
     }
     free(s);
-    return 0;
+    if (! (found || verbose))
+        printf("\n");
+    fflush(stdout);
+}
+
+int main(int argc, char *argv[]) {
+    struct Crypto1State *s, *t;
+    uint64_t key;     // recovered key
+    uint32_t uid;     // serial number
+    uint32_t nt0;      // tag challenge first
+    uint32_t nt1;      // tag challenge second
+    uint32_t nr0_enc; // first encrypted reader challenge
+    uint32_t ar0_enc; // first encrypted reader response
+    uint32_t nr1_enc; // second encrypted reader challenge
+    uint32_t ar1_enc; // second encrypted reader response
+    uint32_t ks2;     // keystream used to encrypt reader response
+
+    if (argc == 8) {
+        printf("MIFARE Classic key recovery - based 32 bits of keystream  VERSION2\n");
+        printf("Recover key from two 32-bit reader authentication answers only\n");
+        printf("This version implements Moebius two different nonce solution (like the supercard)\n\n");
+
+        sscanf(argv[1], "%x", &uid);
+        sscanf(argv[2], "%x", &nt0);
+        sscanf(argv[3], "%x", &nr0_enc);
+        sscanf(argv[4], "%x", &ar0_enc);
+        sscanf(argv[5], "%x", &nt1);
+        sscanf(argv[6], "%x", &nr1_enc);
+        sscanf(argv[7], "%x", &ar1_enc);
+
+        printf("Recovering key for:\n");
+        printf("    uid: %08x\n", uid);
+        printf("   nt_0: %08x\n", nt0);
+        printf(" {nr_0}: %08x\n", nr0_enc);
+        printf(" {ar_0}: %08x\n", ar0_enc);
+        printf("   nt_1: %08x\n", nt1);
+        printf(" {nr_1}: %08x\n", nr1_enc);
+        printf(" {ar_1}: %08x\n", ar1_enc);
+
+        attack(uid, nt0, nr0_enc, ar0_enc, nt1, nr1_enc, ar1_enc, true);
+	return 0;
+    }
+    else if (argc == 2 && ! strncmp(argv[1], "--server", 9)) {
+        char *line =NULL;
+        size_t len = 0;
+        ssize_t line_size;
+	while(true) {
+            line_size = getline(&line, &len, stdin);
+            if (line_size > 1) {
+                sscanf(line, "%x %x %x %x %x %x %x\n", &uid, &nt0, &nr0_enc, &ar0_enc, &nt1, &nr1_enc, &ar1_enc);
+	        attack(uid, nt0, nr0_enc, ar0_enc, nt1, nr1_enc, ar1_enc, false);
+            }
+	    else {
+                break;
+	    }
+	}
+    }
+    else {
+        printf("syntax: %s <uid> <nt> <nr_0> <ar_0> <nt1> <nr_1> <ar_1>\n", argv[0]);
+        printf("        %s --server\n\n", argv[0]);
+        return 1;
+    }
 }