BDSEC

Achieved Rank 3 With HCS

Name	Category	Solved?
Poisoned Ledger Hex	Forensics	✅
Router	Networking	✅

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Poisoned Ledger Hex

TL;DR

Extract the three fragmented OP_RETURN payloads from blocks 101, 108, and 117, concatenate them in block‐order, XOR each byte with 0x42 (ASCII “B”), and you get the flag.

Solution

1. Locate the OP_RETURN fragments

Inspecting each block’s transactions, you find three blocks carrying non‐standard data fields:

• Block 101: OP_RETURN → [0, 6, 17, 7, 1, 57, 0, 14, 114, 1]
• Block 108: OP_RETURN → [9, 29, 1, 10, 3, 11, 44, 29, 6, 55]
• Block 117: OP_RETURN → [47, 18, 29, 115, 119, 29, 4, 55, 44, 44, 27, 63]

2. Reassemble the data\ Concatenate the three arrays in ascending block order to get a single byte stream:

data = [
  0,6,17,7,1,57,0,14,114,1,
  9,29,1,10,3,11,44,29,6,55,
  47,18,29,115,119,29,4,55,44,44,27,63
]

3. Decode with XOR\ The hint (“Poisoned Ledger”) suggests a simple XOR cipher. Using B as the key:

xor_key = ord('B')  # 0x42
decoded = ''.join(chr(b ^ xor_key) for b in data)
print(decoded)

Flag

BDSEC\{BL0CK_CHAIn_DumP_15_FunnY\}

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Router

TL;DR

We need to find a company from the router that is being used from the given pcap file

Solution

We just need to check each of the mac address that is captured from the pcap file and search it on google

Ethernet II, Src: NetisTechnol_47:fa:42 (64:ee:b7:47:fa:42), Dst: LiteonTechno_7e:74:6b (9c:2f:9d:7e:74:6b)

from this website, we know the answer is netis

Flag

BDSEC\{netis\}