createTask
Executing task: Use Ghidra to find key derivation, encryption routine, and embedded constants in /sandbox/cryptooo
ghidra_open_server
ghidra_list_functions
ghidra_decompile_function_by_address
ghidra_decompile_function
ghidra_decompile_function
ghidra_decompile_function
ghidra_decompile_function
ghidra_decompile_function
ghidra_decompile_function
ghidra_decompile_function
ghidra_decompile_function
ghidra_decompile_function
ghidra_decompile_function
ghidra_decompile_function
ghidra_list_data_items
ghidra_get_data_by_address
ghidra_list_strings
ghidra_decompile_function
workspace_read_file
ghidra_get_data_by_address
ghidra_get_data_by_address
ghidra_get_data_by_address
Task Use Ghidra to find key derivation, encryption routine, and embedded constants in /sandbox/cryptooo completed: The static analysis reveals that the program encrypts input data using a two-stage process: first, an in-place encryption combining an RC4-like keystream with a custom block-mixing routine, and second, encoding the result with standard Base64. The RC4 keystream is generated using the base64 alphabet as the key, with the key-scheduling and pseudo-random generation functions explicitly identified. The program features a large, static table (DAT_00401620), which is copied and mixed via a complex routine involving rotations and iterative mixing in FUN_0040064C, ultimately producing a byte stream used in a feedback mode encapsulated by FUN_00400BD2—shifting a 16-byte register and XORing its output with plaintext bytes. The Base64 alphabet constants are initialized within FUN_00400FCE, and the entire encryption pipeline, including the key expansion, keystream generation, and byte feedback, can be precisely reproduced by extracting the static table, implementing the key-expansion and mixing routines according to their decompiled logic, and performing the byte-wise feedback loop. The provided sample ciphertext corresponds to a 32-byte plaintext, allowing the steps to be tested and validated by executing these routines with the exact static data, enabling replication of the encrypted output that base64-encodes to the observed string.
The key is the 64‑byte Base64 alphabet:
ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/
Why: static analysis of /sandbox/cryptooo shows the program builds the Base64 alphabet inside FUN_00400FCE and then calls the RC4 KSA (FUN_00400D35) with that buffer and length 0x40. In other words the program uses the ASCII bytes of the Base64 table as the RC4 key (and then feeds that RC4 state into the custom expansion/keystream generator). You can verify by checking FUN_00400FCE -> FUN_00400F3A -> FUN_00400D35 in the decompilation.
createTask
Executing task: Implement cipher in Python, extract DAT_00401620, decrypt provided base64 ciphertext, return KEY inside SECCON{...}
workspace_list_files
sandbox_execute
sandbox_execute
sandbox_write_file
sandbox_execute
sandbox_execute
sandbox_execute
sandbox_execute
sandbox_execute
sandbox_execute
sandbox_execute
sandbox_execute
sandbox_execute
sandbox_execute
Task Implement cipher in Python, extract DAT_00401620, decrypt provided base64 ciphertext, return KEY inside SECCON{...} completed: Please provide the analysis report for me to summarize.