mirror of
https://github.com/carlospolop/hacktricks
synced 2024-11-26 06:30:37 +00:00
212 lines
9.4 KiB
Markdown
212 lines
9.4 KiB
Markdown
# Cryptographic/Compression Algorithms
|
|
|
|
## Cryptographic/Compression Algorithms
|
|
|
|
{% hint style="success" %}
|
|
Learn & practice AWS Hacking:<img src="/.gitbook/assets/arte.png" alt="" data-size="line">[**HackTricks Training AWS Red Team Expert (ARTE)**](https://training.hacktricks.xyz/courses/arte)<img src="/.gitbook/assets/arte.png" alt="" data-size="line">\
|
|
Learn & practice GCP Hacking: <img src="/.gitbook/assets/grte.png" alt="" data-size="line">[**HackTricks Training GCP Red Team Expert (GRTE)**<img src="/.gitbook/assets/grte.png" alt="" data-size="line">](https://training.hacktricks.xyz/courses/grte)
|
|
|
|
<details>
|
|
|
|
<summary>Support HackTricks</summary>
|
|
|
|
* Check the [**subscription plans**](https://github.com/sponsors/carlospolop)!
|
|
* **Join the** 💬 [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** us on **Twitter** 🐦 [**@hacktricks\_live**](https://twitter.com/hacktricks\_live)**.**
|
|
* **Share hacking tricks by submitting PRs to the** [**HackTricks**](https://github.com/carlospolop/hacktricks) and [**HackTricks Cloud**](https://github.com/carlospolop/hacktricks-cloud) github repos.
|
|
|
|
</details>
|
|
{% endhint %}
|
|
|
|
## Identifying Algorithms
|
|
|
|
If you ends in a code **using shift rights and lefts, xors and several arithmetic operations** it's highly possible that it's the implementation of a **cryptographic algorithm**. Here it's going to be showed some ways to **identify the algorithm that it's used without needing to reverse each step**.
|
|
|
|
### API functions
|
|
|
|
**CryptDeriveKey**
|
|
|
|
If this function is used, you can find which **algorithm is being used** checking the value of the second parameter:
|
|
|
|
 (1) (1) (1) (1).png>)
|
|
|
|
Check here the table of possible algorithms and their assigned values: [https://docs.microsoft.com/en-us/windows/win32/seccrypto/alg-id](https://docs.microsoft.com/en-us/windows/win32/seccrypto/alg-id)
|
|
|
|
**RtlCompressBuffer/RtlDecompressBuffer**
|
|
|
|
Compresses and decompresses a given buffer of data.
|
|
|
|
**CryptAcquireContext**
|
|
|
|
From [the docs](https://learn.microsoft.com/en-us/windows/win32/api/wincrypt/nf-wincrypt-cryptacquirecontexta): The **CryptAcquireContext** function is used to acquire a handle to a particular key container within a particular cryptographic service provider (CSP). **This returned handle is used in calls to CryptoAPI** functions that use the selected CSP.
|
|
|
|
**CryptCreateHash**
|
|
|
|
Initiates the hashing of a stream of data. If this function is used, you can find which **algorithm is being used** checking the value of the second parameter:
|
|
|
|
.png>)
|
|
|
|
\
|
|
Check here the table of possible algorithms and their assigned values: [https://docs.microsoft.com/en-us/windows/win32/seccrypto/alg-id](https://docs.microsoft.com/en-us/windows/win32/seccrypto/alg-id)
|
|
|
|
### Code constants
|
|
|
|
Sometimes it's really easy to identify an algorithm thanks to the fact that it needs to use a special and unique value.
|
|
|
|
.png>)
|
|
|
|
If you search for the first constant in Google this is what you get:
|
|
|
|
.png>)
|
|
|
|
Therefore, you can assume that the decompiled function is a **sha256 calculator.**\
|
|
You can search any of the other constants and you will obtain (probably) the same result.
|
|
|
|
### data info
|
|
|
|
If the code doesn't have any significant constant it may be **loading information from the .data section**.\
|
|
You can access that data, **group the first dword** and search for it in google as we have done in the section before:
|
|
|
|
.png>)
|
|
|
|
In this case, if you look for **0xA56363C6** you can find that it's related to the **tables of the AES algorithm**.
|
|
|
|
## RC4 **(Symmetric Crypt)**
|
|
|
|
### Characteristics
|
|
|
|
It's composed of 3 main parts:
|
|
|
|
* **Initialization stage/**: Creates a **table of values from 0x00 to 0xFF** (256bytes in total, 0x100). This table is commonly call **Substitution Box** (or SBox).
|
|
* **Scrambling stage**: Will **loop through the table** crated before (loop of 0x100 iterations, again) creating modifying each value with **semi-random** bytes. In order to create this semi-random bytes, the RC4 **key is used**. RC4 **keys** can be **between 1 and 256 bytes in length**, however it is usually recommended that it is above 5 bytes. Commonly, RC4 keys are 16 bytes in length.
|
|
* **XOR stage**: Finally, the plain-text or cyphertext is **XORed with the values created before**. The function to encrypt and decrypt is the same. For this, a **loop through the created 256 bytes** will be performed as many times as necessary. This is usually recognized in a decompiled code with a **%256 (mod 256)**.
|
|
|
|
{% hint style="info" %}
|
|
**In order to identify a RC4 in a disassembly/decompiled code you can check for 2 loops of size 0x100 (with the use of a key) and then a XOR of the input data with the 256 values created before in the 2 loops probably using a %256 (mod 256)**
|
|
{% endhint %}
|
|
|
|
### **Initialization stage/Substitution Box:** (Note the number 256 used as counter and how a 0 is written in each place of the 256 chars)
|
|
|
|
.png>)
|
|
|
|
### **Scrambling Stage:**
|
|
|
|
.png>)
|
|
|
|
### **XOR Stage:**
|
|
|
|
.png>)
|
|
|
|
## **AES (Symmetric Crypt)**
|
|
|
|
### **Characteristics**
|
|
|
|
* Use of **substitution boxes and lookup tables**
|
|
* It's possible to **distinguish AES thanks to the use of specific lookup table values** (constants). _Note that the **constant** can be **stored** in the binary **or created**_ _**dynamically**._
|
|
* The **encryption key** must be **divisible** by **16** (usually 32B) and usually an **IV** of 16B is used.
|
|
|
|
### SBox constants
|
|
|
|
.png>)
|
|
|
|
## Serpent **(Symmetric Crypt)**
|
|
|
|
### Characteristics
|
|
|
|
* It's rare to find some malware using it but there are examples (Ursnif)
|
|
* Simple to determine if an algorithm is Serpent or not based on it's length (extremely long function)
|
|
|
|
### Identifying
|
|
|
|
In the following image notice how the constant **0x9E3779B9** is used (note that this constant is also used by other crypto algorithms like **TEA** -Tiny Encryption Algorithm).\
|
|
Also note the **size of the loop** (**132**) and the **number of XOR operations** in the **disassembly** instructions and in the **code** example:
|
|
|
|
.png>)
|
|
|
|
As it was mentioned before, this code can be visualized inside any decompiler as a **very long function** as there **aren't jumps** inside of it. The decompiled code can look like the following:
|
|
|
|
.png>)
|
|
|
|
Therefore, it's possible to identify this algorithm checking the **magic number** and the **initial XORs**, seeing a **very long function** and **comparing** some **instructions** of the long function **with an implementation** (like the shift left by 7 and the rotate left by 22).
|
|
|
|
## RSA **(Asymmetric Crypt)**
|
|
|
|
### Characteristics
|
|
|
|
* More complex than symmetric algorithms
|
|
* There are no constants! (custom implementation are difficult to determine)
|
|
* KANAL (a crypto analyzer) fails to show hints on RSA ad it relies on constants.
|
|
|
|
### Identifying by comparisons
|
|
|
|
.png>)
|
|
|
|
* In line 11 (left) there is a `+7) >> 3` which is the same as in line 35 (right): `+7) / 8`
|
|
* Line 12 (left) is checking if `modulus_len < 0x040` and in line 36 (right) it's checking if `inputLen+11 > modulusLen`
|
|
|
|
## MD5 & SHA (hash)
|
|
|
|
### Characteristics
|
|
|
|
* 3 functions: Init, Update, Final
|
|
* Similar initialize functions
|
|
|
|
### Identify
|
|
|
|
**Init**
|
|
|
|
You can identify both of them checking the constants. Note that the sha\_init has 1 constant that MD5 doesn't have:
|
|
|
|
.png>)
|
|
|
|
**MD5 Transform**
|
|
|
|
Note the use of more constants
|
|
|
|
 (1) (1) (1).png>)
|
|
|
|
## CRC (hash)
|
|
|
|
* Smaller and more efficient as it's function is to find accidental changes in data
|
|
* Uses lookup tables (so you can identify constants)
|
|
|
|
### Identify
|
|
|
|
Check **lookup table constants**:
|
|
|
|
.png>)
|
|
|
|
A CRC hash algorithm looks like:
|
|
|
|
.png>)
|
|
|
|
## APLib (Compression)
|
|
|
|
### Characteristics
|
|
|
|
* Not recognizable constants
|
|
* You can try to write the algorithm in python and search for similar things online
|
|
|
|
### Identify
|
|
|
|
The graph is quiet large:
|
|
|
|
 (2) (1).png>)
|
|
|
|
Check **3 comparisons to recognise it**:
|
|
|
|
.png>)
|
|
|
|
{% hint style="success" %}
|
|
Learn & practice AWS Hacking:<img src="/.gitbook/assets/arte.png" alt="" data-size="line">[**HackTricks Training AWS Red Team Expert (ARTE)**](https://training.hacktricks.xyz/courses/arte)<img src="/.gitbook/assets/arte.png" alt="" data-size="line">\
|
|
Learn & practice GCP Hacking: <img src="/.gitbook/assets/grte.png" alt="" data-size="line">[**HackTricks Training GCP Red Team Expert (GRTE)**<img src="/.gitbook/assets/grte.png" alt="" data-size="line">](https://training.hacktricks.xyz/courses/grte)
|
|
|
|
<details>
|
|
|
|
<summary>Support HackTricks</summary>
|
|
|
|
* Check the [**subscription plans**](https://github.com/sponsors/carlospolop)!
|
|
* **Join the** 💬 [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** us on **Twitter** 🐦 [**@hacktricks\_live**](https://twitter.com/hacktricks\_live)**.**
|
|
* **Share hacking tricks by submitting PRs to the** [**HackTricks**](https://github.com/carlospolop/hacktricks) and [**HackTricks Cloud**](https://github.com/carlospolop/hacktricks-cloud) github repos.
|
|
|
|
</details>
|
|
{% endhint %}
|