feat: add seeded flag generation

.env.example

@@ -1,5 +1,6 @@
 FLAG_LEN=32
 FLAG_FORMAT=ctf{FLAG_GOES_HERE}
+FLAG_SEED=false
 ENCRYPTOR_VENDOR_ID=GenuineIntel
 ENCRYPTOR_MODEL_NAME=Intel(R) Core(TM) i7-6500U CPU @ 2.50GHz
 ENCRYPTOR_OS_VERSION=7.0.3-arch1-2

Makefile

@@ -8,6 +8,7 @@ endif
 # Default configuration
 FLAG_LEN ?= 32
 FLAG_FORMAT ?= ctf{FLAG_GOES_HERE}
+FLAG_SEED ?= false
 
 # Compilation variables
 RISCV_CC ?= riscv64-unknown-elf-gcc
@@ -105,7 +106,7 @@ endif
 
 $(GENERATED): .FORCE
 	mkdir -p $(dir $@)
-	python codegen/generate.py $(FLAG_FORMAT) $(FLAG_LEN) > $@
+	python codegen/generate.py $(FLAG_FORMAT) $(FLAG_LEN) $(FLAG_SEED) > $@
 
 
 build:

README.md

@@ -27,6 +27,7 @@ The provided `.env.example` file contains a sample configuration.
 
 - `FLAG_LEN`: Number, the length of the flag
 - `FLAG_FORMAT`: String, containing the constant `FLAG_GOES_HERE` to be replaced by the flag
+- `FLAG_SEED`: String, the seed used to generate the flag, or `false` if it should be random
 - `ENCRYPTOR_VENDOR_ID`: String, overwrite CPU vendor id. Will use system information if unset
 - `ENCRYPTOR_MODEL_NAME`: String, overwrite CPU model name. Will use system information if unset
 - `ENCRYPTOR_OS_VERSION`: String, overwrite OS version. Will use system information if unset

codegen/generate.py

@@ -1,7 +1,10 @@
 import random
-import secrets
 import sys
 
+def generate_flag(length):
+    characters = list("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789")
+    return "".join([random.choice(characters) for _ in range(length)])
+
 def eprint(*args, **kwargs):
     print("[Codegen]", *args, file=sys.stderr, **kwargs)
 
@@ -47,16 +50,22 @@ def get_check_code(flag_part, user_part, c_mangler):
     return random.choice(variations)
 
 def main():
-    if len(sys.argv) != 3:
-        eprint(f"Usage: {sys.argv[0]} <flag_format> <flag_length>")
+    if len(sys.argv) != 3 and len(sys.argv) != 4:
+        eprint(f"Usage: {sys.argv[0]} <flag_format> <flag_length> [flag_seed]")
         exit(1)
 
     # Flag prefix is not used, currently the flag is just used as-is
     flag_format = sys.argv[1]
     flag_len = int(sys.argv[2])
 
+    if len(sys.argv) >= 4:
+        # We might have a seed
+        flag_seed = sys.argv[3]
+        if flag_seed.lower() != "false":
+            random.seed(flag_seed)
+
     # Generate a secret
-    secret = secrets.token_urlsafe(flag_len)
+    secret = generate_flag(flag_len)
     secret = flag_format.replace("FLAG_GOES_HERE", secret)
 
     eprint(f"Generated Flag: {secret}")