Network challenges from the COlicyber practice track.
Chaos — TCP Payload Reconstruction from PCAP
Filter a PCAP for TCP packets, decode each packet’s payload from hex, and concatenate them in order — the resulting byte stream contains the flag.
Net
Network challenges from COlicyber — PCAP analysis, DNS, TLS, protocol-level exploitation.
Quantum Transport Layer — TLS ALPN Flag via gnutls-cli
The TLS server returns the flag as the negotiated ALPN protocol name. Inject the server’s hostname into /etc/hosts, connect with gnutls-cli specifying –alpn=flag, and read the flag from the TLS handshake output.
Sniff N Byte — Decode Hardcoded Hex Flag
The flag is encoded as concatenated 0x-prefixed hex bytes embedded directly in the capture. Strip the prefixes, decode with bytes.fromhex, and print.
SSA0x42 — XOR Key Recovery from Known-Plaintext PCAP Headers
Two known-plaintext byte sequences (k and l) from the PCAP header XOR to reveal the repeating key. XOR the encrypted flag block with that key to recover the plaintext.
That's a Lot of Fs — Flag in Ethernet Destination MAC via Custom EtherType
Filter Ethernet frames with EtherType 0xffff — the custom protocol used by this challenge — collect the destination MAC address from each matching frame, interpret the first two hex bytes as ASCII, and concatenate to reveal the flag.
Useless — Flag Hidden in PCAPNG via strings
Run strings on the PCAPNG and grep for ‘flag’ — the flag is stored as plain ASCII inside the capture file and visible without any packet parsing.
WordWang — Protocol Format Wrapping
The server returns a word from a custom protocol. Wrap the response in the expected format — prepend ‘?’, uppercase, append ‘!’ — send it back, and the server returns the flag.
You Complete Me — Binary Search Word Reconstruction
A sorted word list and a known sequence of binary-search response sizes pin down a unique word character by character. Reconstruct it by matching the precounted word counts at each prefix level.