Evaluated model output (what the LLM said about the code)
## 1. Functionality
### Observed facts
The snippet contains two functions:
```c
__int64 __fastcall sub_180008BE0(__int64 a1, __int64 a2)
```
and
```c
__int64 __fastcall sub_18001C2F0(int a1)
{
return a1 ^ 0xF03F23B2;
}
```
`sub_180008BE0` takes two pointers:
- `a1`: input buffer
- `a2`: output buffer
If `a2` is NULL, it returns `a1` unchanged.
Otherwise, it iterates byte-by-byte and writes decoded bytes into `a2`.
The core operation is:
```c
*(a2 + i) =
~byte_180025E20[i % 17] & *(a1 + i)
| ~*(a1 + i) & byte_180025E20[i % 17];
```
This expression is equivalent to:
```c
a2[i] = a1[i] ^ byte_180025E20[i % 17];
```
So the function applies a repeating XOR key of length 17 bytes.
The loop terminates when the decoded output contains two consecutive null bytes at an even/odd byte boundary:
```c
if ( i % 2 == 1 && !a2[i] && !a2[i - 1] )
break;
```
The helper function is used to obscure simple constants:
```c
sub_18001C2F0(0xF03F23B0) == 2
sub_18001C2F0(0xF03F23B3) == 1
```
So the condition simplifies to:
```c
if ( i % 2 == 1 && a2[i] == 0 && a2[i - 1] == 0 )
break;
```
### Inferred behavior
This is likely a runtime string decryption routine.
Because the loop stops on two decoded null bytes when `i` is odd, the decoded data is likely UTF-16LE / wide-character string data. A UTF-16LE string terminator is two null bytes:
```text
00 00
```
So the function probably decrypts obfuscated wide strings embedded in the malware.
---
## 2. Well-known algorithms
### Observed
The code implements a repeating-key XOR transformation:
```c
output[i] = input[i] ^ key[i % 17]
```
The key is stored at:
```c
byte_180025E20
```
with an effective length of 17 bytes.
### Inferred
This is not a strong cryptographic algorithm. It is a simple XOR-based string obfuscation scheme commonly used by malware to hide strings, file paths, registry keys, domains, commands, and API names from static analysis.
The XOR operation is deliberately written in a more complex Boolean form:
```c
(~key & input) | (~input & key)
```
which is logically equivalent to:
```c
input ^ key
```
---
## 3. Indicators of Compromise
No concrete IOCs are directly visible in this snippet.
### File paths
None observed.
### IP addresses / domains
None observed.
### Registry keys
None observed.
### Commands or scripts
None observed.
### Other notable constants
| Value | Description |
|---|---|
| `byte_180025E20` | Address of the 17-byte XOR key |
| `0xF03F23B2` | Constant used by helper function for XOR-based constant obfuscation |
| `0xF03F23B0` | Obfuscated value resolving to `2` |
| `0xF03F23B3` | Obfuscated value resolving to `1` |
These are not IOCs by themselves, but they are relevant to the malware’s string decoding logic.
---
## 4. MITRE ATT&CK mapping
### T1027 — Obfuscated Files or Information
**Observed evidence:**
The function decodes data using a repeating XOR key:
```c
a2[i] = a1[i] ^ byte_180025E20[i % 17];
```
The XOR is also written in an intentionally indirect Boolean form:
```c
~key & input | ~input & key
```
The helper function obscures constants:
```c
sub_18001C2F0(0xF03F23B0) == 2
sub_18001C2F0(0xF03F23B3) == 1
```
**Justification:**
Malware commonly stores strings or configuration data in encoded form and decodes them at runtime to avoid static detection and signature-based analysis.
---
### T1140 — Deobfuscate/Decode Files or Information
**Observed evidence:**
The function performs runtime decoding of an input buffer into an output buffer:
```c
*(a2 + i) = decoded_byte;
```
The loop continues until a decoded UTF-16-style null terminator is encountered.
**Justification:**
This is a runtime deobfuscation routine. It likely decodes embedded encrypted strings before use by the malware.
---
## 5. Obfuscation and evasion techniques
### Observed obfuscation
#### 1. Repeating XOR string obfuscation
The function uses a 17-byte repeating XOR key:
```c
byte_180025E20[i % 17]
```
This hides the plaintext content in the binary.
---
#### 2. XOR expressed without the `^` operator
Instead of writing:
```c
input ^ key
```
the code uses:
```c
(~key & input) | (~input & key)
```
This is equivalent to XOR but more difficult to recognize in decompiled output.
---
#### 3. Obfuscated constants
The function avoids literal constants `1` and `2` by computing them through:
```c
sub_18001C2F0(x) = x ^ 0xF03F23B2
```
Examples:
```c
0xF03F23B0 ^ 0xF03F23B2 = 2
0xF03F23B3 ^ 0xF03F23B2 = 1
```
This hides simple loop logic from casual inspection.
---
#### 4. UTF-16LE-style termination check
The loop stops when two consecutive decoded bytes are null and the index is odd:
```c
i % 2 == 1 && a2[i] == 0 && a2[i - 1] == 0
```
This suggests the decoded data is likely wide-character string data.
---
## 6. Summary
### Observed facts
- The code implements a byte-wise XOR decoder.
- The XOR key is located at `byte_180025E20`.
- The key length is 17 bytes.
- The function stops when the decoded output contains `00 00` at an odd index.
- Constants `1` and `2` are hidden using XOR arithmetic.
- No file paths, domains, IP addresses, registry keys, or commands are directly visible in the snippet.
### Inferred behavior
- The function is likely a malware string decryption routine.
- The decoded strings are likely UTF-16LE / wide-character strings.
- The routine is probably used to reveal hidden configuration values, API names, commands, paths, registry keys, or C2 indicators elsewhere in the binary.
- The code uses obfuscation to hinder static analysis and signature generation.
LLM judge panel
ClaudeAI judge verdict:satisfied
{
"understanding_point": "Obfuscated XOR operation",
"full_evaluation": "The summary explicitly and repeatedly identifies that the XOR operation is written in an obfuscated/indirect Boolean form. It states: 'The XOR operation is deliberately written in a more complex Boolean form: (~key & input) | (~input & key) which is logically equivalent to: input ^ key.' It also notes under obfuscation techniques 'XOR expressed without the ^ operator ... This is equivalent to XOR but more difficult to recognize in decompiled output.' This directly and clearly conveys the concept of an obfuscated XOR operation. No contradictions present.",
"explanation": "The summary clearly identifies the XOR operation expressed in an indirect Boolean form (~key & input) | (~input & key), explicitly characterizing it as an obfuscated equivalent of XOR.",
"evidence": "The XOR operation is deliberately written in a more complex Boolean form: (~key & input) | (~input & key) which is logically equivalent to: input ^ key.",
"support_strength": 3,
"satisfied": "true"
}
GeminiAI judge verdict:not_satisfied
{
"understanding_point": "String decryption",
"full_evaluation": "The summary discusses the use of XOR operations for data obfuscation and deobfuscation. It mentions that the code performs bitwise operations on input buffers and that this resembles a simple encryption or obfuscation technique. It also maps the activity to MITRE ATT&CK techniques T1027 (Obfuscated Files or Information) and T1140 (Deobfuscate/Decode Files or Information). While string decryption is a specific type of data deobfuscation, the summary consistently uses general terms like \"data,\" \"buffers,\" \"files or information,\" and \"information.\" It never explicitly states or implies that the target of this deobfuscation process is specifically strings. Therefore, the understanding point is not clearly expressed.",
"explanation": "The summary discusses general data obfuscation and deobfuscation using XOR operations but never specifies that the target of this process is strings. It uses broader terms like 'data' and 'information'.",
"evidence": "The function is likely used for data obfuscation or deobfuscation, given the XOR operations and the use of a predefined byte array.",
"support_strength": 1,
"satisfied": "false"
}
OpenAI judge verdict:satisfied
{
"understanding_point": "Obfuscated XOR operation",
"full_evaluation": "The candidate summary clearly addresses the understanding point. It identifies that the core transformation is an XOR operation and explicitly explains that the XOR is written in an intentionally indirect or obfuscated Boolean form rather than using the ^ operator. The summary provides the Boolean expression (~key & input) | (~input & key), states that it is logically equivalent to input ^ key, and describes this as making the XOR harder to recognize in decompiled output. It also separately notes XOR-based constant obfuscation, but the main required point, an obfuscated XOR operation, is already directly and clearly expressed. There are no contradictions.",
"explanation": "The summary explicitly says the XOR is expressed without the ^ operator using an indirect Boolean form equivalent to XOR. This directly satisfies the point that there is an obfuscated XOR operation.",
"evidence": "Instead of writing:\n\n```c\ninput ^ key\n```\n\nthe code uses:\n\n```c\n(~key & input) | (~input & key)\n```\n\nThis is equivalent to XOR but more difficult to recognize in decompiled output.",
"support_strength": 3,
"satisfied": "true"
}