self-referential-git/commit/be31337

18364853

Author: blaufish

README.md

@@ -0,0 +1,13 @@
+# self-referential-git be31337
+
+[self-referential-git/commit/be31337](https://github.com/blaufish/self-referential-git/commit/be31337)
+
+I just wanted to create a silly git that references itself...
+
+i.e. 
+  `README.md`
+   and commit message should both
+   include the truncated `SHA1` hash.
+
+* [self.bash](self.bash) - a small wrapper for modifying local `.git` if successfull.
+* [self.py](self.py) - a small bruteforce searching for a commit that meets our success condition.

self.bash

@@ -0,0 +1,33 @@
+#!/bin/bash
+
+GUESS="be31337"
+FIRST=$(git rev-parse HEAD | grep -o '^..')
+LAST=$(git rev-parse HEAD | grep -o '......................................$')
+
+if git rev-parse HEAD | grep $GUESS
+then
+	echo "Success allready: "
+	git rev-parse HEAD
+	exit
+fi
+
+rm -- hack.msg hack.msg.4 hack.msg.trunc hack.msg.zlib
+
+./self.py .git/objects/$FIRST/$LAST $GUESS hack.msg hack.msg.zlib
+
+set -x
+
+SHA=$(shasum hack.msg | awk '{print $1}' )
+FIRST=$(shasum hack.msg | awk '{print $1}' | grep -o '^..')
+LAST=$(shasum hack.msg | awk '{print $1}' | grep -o '......................................$')
+
+git rev-parse HEAD
+mkdir -p ".git/objects/$FIRST"
+file hack.msg.zlib
+cp -- hack.msg.zlib ".git/objects/$FIRST/$LAST"
+
+set -e
+git cat-file -p "$SHA"
+
+shasum hack.msg > .git/HEAD
+git rev-parse HEAD

self.py

@@ -0,0 +1,57 @@
+#!/usr/bin/env python3
+
+import hashlib
+import os
+import sys
+import threading
+import zlib
+
+lock = threading.Lock()
+terminate = False;
+
+def hack(git_object, counter_start, counter_increment, goal, destination_clear, destination_compressed):
+    global lock
+    global terminate
+    print(f"hack(..., {counter_start}, {counter_increment}, {goal})", file=sys.stderr);
+    header, content = git_object.split(b'\x00', 1)
+    hack_str = content.decode("utf-8")
+    counter = counter_start;
+    while True:
+        with lock:
+            if terminate:
+                return
+        commit_content = hack_str + "\n" + str(counter) + "\n"
+        commit_content_bytes = commit_content.encode("utf-8")
+        commit_content_bytes_len = len(commit_content_bytes)
+        header = f"commit {commit_content_bytes_len}\x00"
+        header_content = header + commit_content
+        to_be_hashed = header_content.encode("utf-8")
+        s = hashlib.sha1(to_be_hashed).hexdigest()
+        if s.startswith(goal):
+            with lock:
+                terminate = True
+            print(f"SHA1: {s}", file=sys.stderr);
+            print(f"Write to: {destination_clear} (plain)", file=sys.stderr);
+            with open(destination_clear, "wb") as f:
+                f.write(to_be_hashed)
+            print(f"Write to: {destination_compressed} (compressed)", file=sys.stderr);
+            with open(destination_compressed, "wb") as f:
+                bb = zlib.compress(to_be_hashed)
+                f.write(bb)
+            return
+        counter = counter + counter_increment
+
+filename = sys.argv[1]
+compressed_contents = open(filename, 'rb').read()
+decompressed_contents = zlib.decompress(compressed_contents)
+#print(f"------\n{s}\n------)", file=sys.stderr);
+
+cpus = len(os.sched_getaffinity(0))
+print(f"\rCPUs detected: {cpus}", file=sys.stderr)
+
+threads = [threading.Thread(target=hack, args=(decompressed_contents,i,cpus,sys.argv[2], sys.argv[3], sys.argv[4])) for i in range(0, cpus)]
+for thread in threads:
+    thread.start()
+
+for thread in threads:
+    thread.join()