Testing: fuzz MTProto obfuscated2 frame parser

[dvershinin]

Context

Follow-up from #51. The obfuscated2 frame parser was not included in the initial fuzz testing work because it is deeply coupled to AES crypto and connection state.

What needs fuzzing

In net/net-tcp-rpc-ext-server.c, the obfuscated2 handshake path:

• 64-byte random header parsing
• AES-CTR key/IV derivation from the header
• Tag detection at offset 56 after decryption (0xdddddddd, 0xeeeeeeee, 0xefefefef)
• Target DC extraction at offset 60
• Compact/medium frame length parsing (1-byte and 4-byte variants)

Approach

Requires refactoring to decouple from:

• connection_info structs and rwm_* message buffers
• AES encryption context setup (net-crypto-aes.c)
• Global state (ext_secret, connection type tables)

One approach: extract the post-decryption parsing (tag detection, DC extraction, frame length validation) into a standalone function that takes a flat 64-byte buffer.

Priority

Medium — this code handles untrusted input but only after the initial TLS/obfuscated2 layer is negotiated.

[github-actions]

Thank you for opening this issue.

This project is maintained by a single developer in their free time.
Upstream TelegramMessenger/MTProxy is abandoned. This fork is the only actively maintained version.

Continued development depends on community support:

• GitHub Sponsors — sponsors' issues are prioritized
• TON: UQBOGq_b3eL63Qfkj6ykoBibK3zGJDQzLK91v2q-UCY7BPeb (send via @wallet in Telegram)
• USDT (TRC-20): TNVSj1QjZ5jqdaeshe7VCpXWo2S1n936Hj
• BTC: bc1qvxxldmanwggula7992uun5a2qxm65ej9h0unj7
• GetPageSpeed RPM packages — production-ready install with support

Issues without community interest may be closed after 60 days of inactivity.