Cert Keyfinder Apk Parsing

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Introduction

Overview: CERT Keyfinder is a tool designed to find and analyze key files on filesystems and within Android APK files, originally developed as part of an experiment related to Android apps.
Funding: This tool was sponsored by the United States Department of Homeland Security, highlighting its significance and trustworthiness in secure key management practices.
Capabilities: It supports the parsing of Android APK files, while also identifying private and password-protected key files by default on the filesystem.
Installation Requirements: Keyfinder requires Python (3.x recommended), along with packages like androguard, python-magic, and PyOpenSSL, among others.
Usage Examples: The tool is effectively used for scanning for key files within APKs, utilizing OpenSSL and Java keytool utilities for key parsing and verification.

Python Requirement: CERT Keyfinder functions best with Python 3.x.
Dependencies: Installation requires packages like androguard, python-magic, PyOpenSSL, and apktool.
System Tools: Additional tools like grep, OpenSSL, and Java are necessary for full functionality.
Windows Adjustment: For Windows users, 'python-magic-bin' must be used instead of 'python-magic'.
Repository Access: Users can clone the Keyfinder repository from github to obtain the software.

APK Support: CERT Keyfinder can parse APK files to find key files located within the APK structure.
Key Identification: The tool identifies Java KeyStore and BouncyCastle Keystore files, among others, within APKs.
Extracted Information: It can identify information about key files, such as password protection status and type.
crt.sh Queries: It uses key SHA256 signatures to check key/public key occurrences in public databases like crt.sh.
Security Implications: Identifies if private keys in APKs appear in publicly accessible repositories, flagging potential security concerns.

Command Line Usage: Operate the tool using command-line inputs, such as $ python3 keyfinder.py [apkpath].
Extract & Analyze: Use options to extract APK contents and analyze key files with or without verbose output.
Debugging: Enable debugging with -d flag for more detailed analysis output.
Password Support: The tool can specify passwords for key file inspection using -p flag.
Verbose Mode: Add -v flag for detailed output, displaying full certificate information when available.

Error 8674: Encountered when parsing CERT.RSA files not in PKCS format.
mbedtls Compatibility: The mbedtls_x509_crt_parse function does not support some PKCS formats directly.
Conversion Solution: Using OpenSSL to convert CERT.RSA to PEM format for compatibility with mbedtls.
Public Key Extraction: Challenges in reliably extracting only public key from CERT.RSA using various libraries.
Command Line Absence: Difficulty arises without command-line access for format conversions.

crt.sh Queries: Keyfinder queries crt.sh for any key's SHA256 signature to verify its public occurrence.
Security Concerns: Detection of keys in public databases indicates potential security risks.
Transparency Logs: crt.sh monitors certificate transparency sources, helping check key legitimacy.
Private Key Alerts: If a private key is found publicly, it raises significant security issues.
Database Linkage: Keyfinder can link discovered keys to their corresponding entries in crt.sh, providing detailed background.

APK Key Exposure: Distributing APKs that contain private keys can lead to serious security drawbacks.
Sensitive Data: Managing and protecting keys is crucial for securing Android applications.
Transparent Reporting: Ensure transparency in key file reporting to mitigate exposure risks.
Public Key Risks: Publicly available keys in APKs can compromise server security or affect user trust.
Best Practices: Following Google's key management guidelines is strongly advised to ensure security.