forensics/trivial_flag_transfer_protocol

2026-07-02 03:55:14 +09:00
parent ae8bd808bb
commit 11fa451ca2
2 changed files with 49 additions and 0 deletions
@@ -0,0 +1 @@
+picoCTF{h1dd3n_1n_pLa1n_51GHT_18375919}
@@ -0,0 +1,48 @@
+#!/usr/bin/env nix-shell
+#!nix-shell -i bash -p tshark xxd steghide
+
+# NOTE: tftp.pcanpng is big, has been omitted
+
+mapfile -t FILE_REQS < <( \
+  tshark -r tftp.pcapng \
+    -Y "(ip.src==10.10.10.11 && tftp.opcode==1) || (ip.src==10.10.10.11 && tftp.opcode==2)" \
+    -T fields \
+    -e tftp.source_file \
+    -e tftp.destination_file \
+  | sed 's/\t//' \
+  | uniq \
+)
+
+mapfile -t STREAMS < <( \
+  tshark -r tftp.pcapng \
+  -Y "(ip.dst==10.10.10.11 && tftp.opcode==3) || (ip.dst==10.10.10.11 && tftp.opcode==4)" \
+  -T fields -e udp.stream \
+  | sort -nu \
+)
+
+mkdir -p out
+
+for i in "${!FILE_REQS[@]}"; do
+  FILENAME="${FILE_REQS["$i"]}"
+  UDP_STREAM="${STREAMS["$i"]}"
+
+  echo "$FILENAME -> $UDP_STREAM"
+
+  tshark -r tftp.pcapng \
+      -Y "udp.stream==$UDP_STREAM && ((ip.dst==10.10.10.11 && tftp.opcode==3) || (ip.src==10.10.10.11 && data.len!=4))" \
+      -T fields -e data.data |
+  tr -d '\n' |
+  xxd -r -p > "out/$FILENAME"
+done
+
+# NOTE: the deb file contained steghide, assuming the plan is the passphrase for one of the pics
+
+cat out/instructions.txt | tr 'A-Za-z' 'N-ZA-Mn-za-m'
+cat out/plan | tr 'A-Za-z' 'N-ZA-Mn-za-m'
+
+STEGHIDE_PW="DUEDILIGENCE"
+
+steghide extract --stegofile out/picture1.bmp --passphrase "$STEGHIDE_PW" ||:
+steghide extract --stegofile out/picture2.bmp --passphrase "$STEGHIDE_PW" ||:
+steghide extract --stegofile out/picture3.bmp --passphrase "$STEGHIDE_PW" ||:
+