Reverse Engineering

Dynamic Binary Instrumentation

Why?

  • Requests to APIs are further encrypted or signed or MITM is not available.

    • MITM and packet sniffers are useless.

  • Application has obfuscated values in RAM, created dynamically, and received from the network.

    • Static analysis and Decompilation are useless.

  • Code is loaded dynamically with objects received.

    • Static analysis and Decompilation will have no code to analyze.

  • Many values are hard coded (keys, urls…).

    • Patching takes too long and becomes expensive.

Custom Signatures are used.

POST /login HTTP/1.1
Host: social.io
Proxy-Connection: keep-alive
Content-Length: X
Accept: text/html, application/xhtml-
xml,application/xml;q=0.9,image/webp,*/*,q=0.8
Origin: http://social.io
Content-Type: application/x-www-form-urlencoded
Cookie: SessionId=O+qxnaYZLjpnLwHBcKmRcTexTWk=

username=john&password=xpto&signature=2rf+roJPEdCOSL0XXusHBcA0BGk=

Data is encrypted.

POST /login HTTP/1.1
Host: social.io
Proxy-Connection: keep-alive
Content-Length: X
Accept: text/html, application/xhtml-
xml,application/xml;q=0.9,image/webp,*/*,q=0.8
Origin: http://social.io
Content-Type: application/x-www-form-urlencoded
Cookie: SessionId=O+qxnaYZLjpnLwHBcKmRcTexTWk=

authData=3NH71S+7P8YeafgnBvXzJ1RzJdXm51VNPQYMWFiIMl8ZNr7+vGDNTcms8LHDUaC/lK2xRF/L
bPMwQ0pB+ZyB6PfYNaf5fIh/IGdlQZJrgXXgDDT7Mn2d259vzcdmBA3pJ04cLxGNnLSvdorYF+mLN7yik
zEagUWGfQe1nYzu3OT3947kqSORQuc4PTzuFKUXlolCcuVYvr5gt6ykfk9ACGVwyywGBG3OeFxNKi0kme
iBYxB8EJlmCF/xojM59gcGDv61ytidhVs=

Other purposes

  • Retrieving a call flow.

    • Map which methods are used, and what is the actual code execution flow.

  • Identify arguments of Android API methods.

    • Log traffic and calls.

    • Allows intercepting data even with encrypted connections.

      • Interception happens before data is encrypted.

  • Modify arguments of Android API methods.

    • Fuzzing.

    • Filter/modify data to trigger additional behaviour.

    • Trigger custom events.

  • Circumvent protections to enable further analysis.

  • The application is obfuscated and it is difficult to obtain the actual algorithm.

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