Fake RTO Challan Checker Part 2 Cracking the Payload, Mappin...

[carlospolop]

🤖 Automated Content Update

This PR was automatically generated by the HackTricks News Bot based on a technical blog post.

📝 Source Information

• Blog URL: https://medium.com/@singhbkn07/fake-rto-challan-checker-part-2-cracking-the-payload-mapping-the-operator-and-why-this-is-3eb78e512d7f
• Blog Title: Fake RTO Challan Checker Part 2: Cracking the Payload, Mapping the Operator, and Why This Is Worse Than I Thought
• Suggested Section: Mobile Pentesting > Android Applications Pentesting > Manual DeObfuscation / Reversing Native Libraries; optionally cross-reference Basic Forensic Methodology > Malware Analysis

🎯 Content Summary

This blog post is a technical static reverse-engineering teardown of RTOChallanCheck.apk, an Android malware sample distributed through WhatsApp while impersonating an Indian government RTO traffic challan checker. The APK’s important components were a native ARM64 library named libtonk.so and a high-entropy 8 MB encrypted asset named NhO0Y. The analysis shows that NhO0Y is the encrypted container for the real malware platform, and that the ...

🔧 Technical Details

Static recovery of OLLVM-encrypted strings in native Android malware: When an Android native library decrypts strings in place through repeated byte-wise XOR instructions, the decryptor can often be reconstructed without executing the malware. Look for patterns such as ldrb, mov, eor, and strb, or their decompiler equivalent DAT_addr ^= 0xNN. Extract the address-to-XOR-key mapping, apply it to the relevant ELF data section, and recover the plaintext strings offline. This is useful when OLLVM string encryption hides JNI method names, crypto constants, asset paths, or C2 indicators.

Encrypted Android asset unpacking from recovered crypto constants: Malware may hide payloads as high-entropy asset files and decrypt them from native code. In this case, the decryptor derived seed = asset_name + "2", then used SHA-1(seed)[0:16] as the AES key and SHA...

🤖 Agent Actions

Done.

Updated:

• src/mobile-pentesting/android-app-pentesting/manual-deobfuscation.md

Added concise reusable content for:

• offline recovery of OLLVM-style native XOR string decryptors
• rebuilding filename-derived AES/CBC asset decryptors
• StringFog Base64 + repeating-XOR deobfuscation
• analyzing split APKs / HTML assets / loaders as one staged payload chain

Also added the Medium blog URL to the file’s ## References and Further Reading.

Validation:

• Reviewed the diff and final file contents
• Tried mdbook build, but mdbook is not installed in this environment (/bin/bash: mdbook: command not found)

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[carlospolop]

🔗 Additional Context

Original Blog Post: https://medium.com/@singhbkn07/fake-rto-challan-checker-part-2-cracking-the-payload-mapping-the-operator-and-why-this-is-3eb78e512d7f

Content Categories: Based on the analysis, this content was categorized under "Mobile Pentesting > Android Applications Pentesting > Manual DeObfuscation / Reversing Native Libraries; optionally cross-reference Basic Forensic Methodology > Malware Analysis".

Repository Maintenance:

• MD Files Formatting: 974 files processed

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Bot Version: HackTricks News Bot v1.0