chained-forensic-extraction_20260101_011957

{"output": "total 16\ndrwxr-xr-x 1 root root 4096 Mar  4 09:22 .\ndrwxr-xr-x 1 root root 4096 Apr 22 18:14 ..\ndrwxr-xr-x 2 root root 4096 Mar  4 09:22 data\ndrwxr-xr-x 2 root root 4096 Mar  4 09:22 output", "exit_code": 0, "error": null}

I'll analyze this multi-stage forensic extraction challenge and work through each stage systematically.

Let me start by exploring the environment and examining the artifact file.

→ terminal({"command": "ls -la /app/"})

{"output": "total 12\ndrwxr-xr-x 2 root root 4096 Mar  4 09:22 .\ndrwxr-xr-x 1 root root 4096 Mar  4 09:22 ..\n-rw-r--r-- 1 root root  957 Mar  4 09:22 artifact.bin\ntotal 8\ndrwxr-xr-x 2 root root 4096 Mar  4 09:22 .\ndrwxr-xr-x 1 root root 4096 Mar  4 09:22 ..", "exit_code": 0, "error": null}

{"output": "bash: line 3: xxd: command not found", "exit_code": 0, "error": null}

{"output": "Size: 957 bytes\nFirst 200 bytes:\n50 4f 4c 59 47 4c 4f 54 5f 48 45 41 44 45 52 00 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f 20 21 22 23 24 25 26 27 28 29 2a 2b 2c 2d 2e 2f 30 31 32 33 34 35 36 37 38 39 3a 3b 3c 3d 3e 3f 50 4b 03 04 14 00 00 00 00 00 c1 4a 64 5c 9a d0 ee ca 3d 00 00 00 3d 00 00 00 09 00 00 00 64 65 63 6f 79 2e 74 78 74 54 68 69 73 20 69 73 20 61 20 64 65 63 6f 79 20 66 69 6c 65 2e 20 54 68 65 20 72 65 61 6c 20 64 61 74 61 20 69 73 20 69 6e 20 74 68 65 20 73 65 63 6f 6e 64 20 61 72 63 68 69 76 65 2e 50 4b 01 02 14 03 14 00 00 00 00 00 c1 4a 64 5c 9a d0 ee ca", "exit_code": 0, "error": null}

{"output": "Found 2 ZIP signatures at offsets: [80, 336]", "exit_code": 0, "error": null}

Good! I can see the file structure. I can see:
1. A "POLYGLT_HEADER" marker (bytes 0-15)
2. ZIP signature (0x504b0304) at offset 0x40 (64 bytes)
3. The first ZIP appears to be a decoy with "decoy.txt"

Let me search for all ZIP signatures in the file:

→ terminal({"command": "python3 -c \"\ndata = open('/app/data/artifact.bin', 'rb').read()\nimport struct\n\n# Find all ZIP signatures (0x504b0304)\nzip_signatures = []\nfor i in range(len(data) - 4):\n    if data[i:i+4] == b'PK\\x03\\x04':\n        zip_signatures.append(i)\n\nprint(f'Found {len(zip_signatures)} ZIP signatures at offsets: {zip_signatures}')\n\""})

{"bytes_written": 1770, "dirs_created": true}

{"output": "Found 2 ZIP signatures at offsets: [80, 336]\nFirst ZIP (decoy) offset: 80\nSecond ZIP (real) offset: 336\n\nSecond ZIP contents: ['hidden.png']\n  hidden.png: 503 bytes\n  Extracted hidden.png (503 bytes)\n\nStage 1 complete.", "exit_code": 0, "error": null}

{"bytes_written": 3364, "dirs_created": true}

Stage 1 complete. Now let me work on Stage 2 - PNG chunk verification:

→ write_file({"path": "/app/stage2.py", "content": "#!/usr/bin/env python3\n\"\"\"Stage 2: PNG Chunk Verification\"\"\"\nimport struct\n\ndef calculate_crc32(data, initial_crc=0):\n    \"\"\"Calculate CRC-32 using the standard polynomial\"\"\"\n    crc = initial_crc ^ 0xFFFFFFFF\n    for byte in data:\n        crc ^= byte\n        for _ in range(8):\n            if crc & 1:\n                crc = (crc >> 1) ^ …)

{"output": "PNG file size: 503 bytes\nPNG signature: 89504e470d0a1a0a\n\nFound 4 chunks:\n  Chunk 0: offset=8, type='IHDR', length=13\n    CRC valid: True (stored=3a7e9b55, calc=3a7e9b55)\n  Chunk 1: offset=33, type='tEXt', length=424\n    CRC valid: True (stored=3890872c, calc=3890872c)\n    tEXt content: Comment\u0000LSgsK3VvM28uKCApcRdxEW48GDExAmkMLhdpLmM5aSMscRgTI3FoETwrcT4tKDQXbDltMC0XaSkyYiBtMGw/CDNiDj0tFhgfPAACaWk/MzZtbxgJbTk1biIYNSI7GB0pM2MgaTA/Chs/Kiw8aG0zKXU8HD0tNQMKMyo2PmIYAws8Khw9NgwOKW4ZNCtvFjMtIxcpPCNtMw11PDY+LShxEm0MGTMgcTQLbDl1MDsYbCt1PWgLIjULCj1jbG1iMmgdLyhsEHENCyBvDTsiNwI3DHU8NmwwAykLbxlsPmlxbQsyKWgoaT5pNG09cWwtDBgfPAACaWk/MzZsORgJbTk1biIYNSI7KB1xIHFsAGwMPzYgMjYCbRgdbz08LXE2AjUDPWIOPmIYAww8ACAVMAN1KT0qLDwiMGdn\n    tEXt offset within PNG: 33\n  Chunk 2: offset=469, type='IDAT', length=10\n    CRC valid: True (stored=48afa471, calc=48afa471)\n  Chunk 3: offset=491, type='IEND', length=0\n    CRC valid: True (stored=ae426082, calc=ae426082)\n\ntEXt chunk details:\n  Offset: 33\n  CRC valid: True\n  Content: Comment\u0000LSgsK3VvM28uKCApcRdxEW48GDExAmkMLhdpLmM5aSMscRgTI3FoETwrcT4tKDQXbDltMC0XaSkyYiBtMGw/CDNiDj0tFhgfPAACaWk/MzZtbxgJbTk1biIYNSI7GB0pM2MgaTA/Chs/Kiw8aG0zKXU8HD0tNQMKMyo2PmIYAws8Khw9NgwOKW4ZNCtvFjMtIxcpPCNtMw11PDY+LShxEm0MGTMgcTQLbDl1MDsYbCt1PWgLIjULCj1jbG1iMmgdLyhsEHENCyBvDTsiNwI3DHU8NmwwAykLbxlsPmlxbQsyKWgoaT5pNG09cWwtDBgfPAACaWk/MzZsORgJbTk1biIYNSI7KB1xIHFsAGwMPzYgMjYCbRgdbz08LXE2AjUDPWIOPmIYAww8ACAVMAN1KT0qLDwiMGdn\n\nStage 2 complete.", "exit_code": 0, "error": null}

{"bytes_written": 3553, "dirs_created": true}

Great! Stage 2 complete. I can see the tEXt chunk content (after the "Comment\0" marker). The text is the encoded data. Now let me work on Stage 3 - decoding the encoding chain:

→ write_file({"path": "/app/stage3.py", "content": "#!/usr/bin/env python3\n\"\"\"Stage 3: Encoding Chain Decode\"\"\"\nimport base64\nimport json\n\ndef rot13(s):\n    \"\"\"Apply ROT13 transformation\"\"\"\n    result = []\n    for c in s:\n        if 'a' <= c <= 'z':\n            result.append(chr((ord(c) - ord('a') + 13) % 26 + ord('a')))\n        elif 'A' <= c <= 'Z':\n            result.append(chr((ord(c…)

{"output": "Encoded data (first 100 chars): LSgsK3VvM28uKCApcRdxEW48GDExAmkMLhdpLmM5aSMscRgTI3FoETwrcT4tKDQXbDltMC0XaSkyYiBtMGw/CDNiDj0tFhgfPAAC\nEncoded data length: 416\nNo valid XOR key found!", "exit_code": 0, "error": null}

{"output": "First 200 chars of encoded data:\nLSgsK3VvM28uKCApcRdxEW48GDExAmkMLhdpLmM5aSMscRgTI3FoETwrcT4tKDQXbDltMC0XaSkyYiBtMGw/CDNiDj0tFhgfPAACaWk/MzZtbxgJbTk1biIYNSI7GB0pM2MgaTA/Chs/Kiw8aG0zKXU8HD0tNQMKMyo2PmIYAws8Khw9NgwOKW4ZNCtvFjMtIxcpPCNt\n\nLength: 416\nFirst 50 bytes of base64 decode: b'-(,+uo3o.( )q\\x17q\\x11n<\\x1811\\x02i\\x0c.\\x17i.c9i#,q\\x18\\x13#qh\\x11<+q>-(4\\x17l9'", "exit_code": 0, "error": null}

The XOR key wasn't found. Let me reconsider - the encoding order might be different. Let me check the encoded data more carefully and try different approaches:

→ terminal({"command": "python3 -c \"\nimport base64\n\n# Read the extracted text\nwith open('/app/output/stage2_result.json', 'r') as f:\n    import json\n    data = json.load(f)\n\n# Extract the tEXt content (after the 'Comment\\\\0' marker)\nfull_text = data['stage2_png']['png_extracted_text']\nencoded_data = full_text.split('\\x00', 1)[1] if '\\x00' in full_text else full_text\n\nprint('First 200 chars o…)

{"bytes_written": 3591, "dirs_created": true}

The base64 decode gives binary data. Let me think about this differently - maybe the encoding chain is:
1. ROT13 applied to the original data
2. Then XOR
3. Then Base64

So to decode, I need to:
1. Base64 decode
2. XOR (try all keys)
3. ROT13

Let me try this approach:

→ write_file({"path": "/app/stage3_v2.py", "content": "#!/usr/bin/env python3\n\"\"\"Stage 3: Encoding Chain Decode - Try different order\"\"\"\nimport base64\nimport json\n\ndef rot13(s):\n    \"\"\"Apply ROT13 transformation\"\"\"\n    result = []\n    for c in s:\n        if 'a' <= c <= 'z':\n            result.append(chr((ord(c) - ord('a') + 13) % 26 + ord('a')))\n        elif 'A' <= c <= 'Z':\n           …)

{"output": "Encoded data (first 100 chars): LSgsK3VvM28uKCApcRdxEW48GDExAmkMLhdpLmM5aSMscRgTI3FoETwrcT4tKDQXbDltMC0XaSkyYiBtMGw/CDNiDj0tFhgfPAAC\nEncoded data length: 416\nBase64 decoded length: 312\nFirst 50 bytes: 2d282c2b756f336f2e282029711771116e3c18313102690c2e17692e633969232c711813237168113c2b713e2d2834176c39\n\n*** FOUND KEY: 69 ***\n  XOR decoded (first 50): hmin0*v*kmel4R4T+y]ttG,IkR,k&|,fi4]Vf4-Tyn4{hmqR)|\n  ROT13 decoded: uzva0*i*xzry4E4G+l]ggT,VxE,x&|,sv4]Is4-Gla4{uzdE)|(huE,yj'r(h)mZi'XkuF]MlRT,,mif(*]Y(|c+t]ct~]Kyi&r,\n\nStage 3 complete. XOR key: 69", "exit_code": 0, "error": null}

{"bytes_written": 3926, "dirs_created": true}

The output doesn't look right. Let me reconsider the problem. The encoding chain says:
1. ROT13 applied first
2. Then XOR
3. Then Base64

So the original data was: `rot13(plain) -> xor -> base64`

To decode: `base64 -> xor -> rot13`

But the output doesn't look like valid text. Let me check if the XOR key produces valid output when we apply ROT13 first:

→ write_file({"path": "/app/stage3_v3.py", "content": "#!/usr/bin/env python3\n\"\"\"Stage 3: Encoding Chain Decode - Try all combinations\"\"\"\nimport base64\nimport json\nimport string\n\ndef rot13(s):\n    \"\"\"Apply ROT13 transformation\"\"\"\n    result = []\n    for c in s:\n        if 'a' <= c <= 'z':\n            result.append(chr((ord(c) - ord('a') + 13) % 26 + ord('a')))\n        elif 'A' <= c <= '…)

{"output": "Encoded data (first 100 chars): LSgsK3VvM28uKCApcRdxEW48GDExAmkMLhdpLmM5aSMscRgTI3FoETwrcT4tKDQXbDltMC0XaSkyYiBtMGw/CDNiDj0tFhgfPAAC\nBase64 decoded length: 312\n\n*** FOUND KEY: 64 ***\n  ROT13 decoded: zuyx5/f/au`v1J1D.|KddO)YaJ)a#l)py1KFp1(D|x1~zugJ,l-czJ)ve\"`-c,Uf\"A}zIK_|@O))fi-/KV-lh.oKho{K]vf#`)\n\n--- Trying reverse order: base64 -> rot13 -> xor ---\n\n*** FOUND KEY: 0 (reverse order) ***\n  XOR decoded: YFtfX3IiZ28hXPNcpEqkRJ48TQRkNzxZYuqcYzZ5nFZfpEtGV3SbRGjepG4gXQDKoQygZP0KnFxlLvOgZTj/PQAvQw0gSutsCNNP\n\nStage 3 complete. XOR key: 0", "exit_code": 0, "error": null}

{"output": "", "exit_code": 0, "error": null}

The XOR key 0 means no XOR was applied, which is suspicious. Let me look at this more carefully. The challenge says the encoding chain is applied in order: ROT13, then XOR, then Base64. Let me check if there's a pattern in the encoded data:

→ terminal({"command": "python3 -c \"\nimport base64\n\n# Read the extracted text\nwith open('/app/output/stage2_result.json', 'r') as f:\n    import json\n    data = json.load(f)\n\nfull_text = data['stage2_png']['png_extracted_text']\nencoded_data = full_text.split('\\x00', 1)[1]\n\n# Try XOR with different keys and see what makes sense\nfor key in [0, 1, 2, 13, 26, 42, 55, 64, 69, 88, 127]:\n    b64_decod…)

{"bytes_written": 4464, "dirs_created": true}

Let me think about this differently. The challenge says the encoding chain is:
1. ROT13
2. XOR with single-byte key
3. Base64

And the output "must be valid Base64 string" after decoding. Let me re-read the challenge more carefully. It says:
- "decoded_intermediate": The result after decoding the chain (must be valid Base64 string)

So the output should be Base64, not the final plaintext. Let me try a different approach - maybe I need to find the XOR key that produces valid Base64 output:

→ write_file({"path": "/app/stage3_v4.py", "content": "#!/usr/bin/env python3\n\"\"\"Stage 3: Encoding Chain Decode - Find key that produces valid Base64\"\"\"\nimport base64\nimport json\nimport string\n\ndef rot13(s):\n    \"\"\"Apply ROT13 transformation\"\"\"\n    result = []\n    for c in s:\n        if 'a' <= c <= 'z':\n            result.append(chr((ord(c) - ord('a') + 13) % 26 + ord('a')))\n        eli…)

{"output": "Encoded data (first 100 chars): LSgsK3VvM28uKCApcRdxEW48GDExAmkMLhdpLmM5aSMscRgTI3FoETwrcT4tKDQXbDltMC0XaSkyYiBtMGw/CDNiDj0tFhgfPAAC\nLength: 416\nBase64 decoded length: 312\nNo valid solution found with base64 -> xor -> rot13 order!\n\n--- Trying: base64 -> rot13 -> xor ---\n\n*** FOUND KEY: 0 (alt order) ***\n  XOR decoded (first 50): YFtfX3IiZ28hXPNcpEqkRJ48TQRkNzxZYuqcYzZ5nFZfpEtGV3\n  Is valid Base64: True\n\nStage 3 complete. XOR key: 0", "exit_code": 0, "error": null}

{"output": "Full tEXt content (repr):\n'Comment\\x00LSgsK3VvM28uKCApcRdxEW48GDExAmkMLhdpLmM5aSMscRgTI3FoETwrcT4tKDQXbDltMC0XaSkyYiBtMGw/CDNiDj0tFhgfPAACaWk/MzZtbxgJbTk1biIYNSI7GB0pM2MgaTA/Chs/Kiw8aG0zKXU8HD0tNQMKMyo2PmIYAws8Khw9NgwOKW4ZNCtvFjMt'\n\nSplit by null byte:\nNumber of parts: 2\nPart 0: 7 chars, starts with: Comment\nPart 1: 416 chars, starts with: LSgsK3VvM28uKCApcRdxEW48GDExAmkMLhdpLmM5aSMscRgTI3", "exit_code": 0, "error": null}

Key 0 means no XOR was applied, which is suspicious. Let me look at the raw data more carefully - maybe the encoding is different. Let me check if the "Comment\0" marker is part of the encoding or if the text after it is the encoded data:

→ terminal({"command": "python3 -c \"\n# Read the extracted text\nwith open('/app/output/stage2_result.json', 'r') as f:\n    import json\n    data = json.load(f)\n\nfull_text = data['stage2_png']['png_extracted_text']\nprint('Full tEXt content (repr):')\nprint(repr(full_text[:200]))\nprint()\nprint('Split by null byte:')\nparts = full_text.split('\\x00')\nprint(f'Number of parts: {len(parts)}')\nfor i, part…)