Skip to main content

3 key 3DES, 2 key 3DES and effective security

There was a recent discussion around effective security and effective key length of 3DES algo. Basically the 3 DES is 3 times DES. There would be 3 keys (K1, K2, K3 ) involved in the operation. The size of a key in DES is 64 bit, but due to padding the actual keys being used for the encryption are 56 bits of the length. So, in 3DES the the total key size would be 168 bits.
Now there are 3 options in 3DES:
Option 1, where K1, K2, and K3  are independent, the length would be 168 bits.
Option 2, where 2 keys are similar , eg, K1=K3, still the actual length is 168 bits but the 'effective' length would be 112 bits. (also called 2-key 3DES)
Option 3, the least secure where all three keys are same, ie, K1=K2=K3, still the actual length is 168 bits, the 'effective' key length would be 56 bits.

Now due to a know attack on 3DES, Meet-In-the-Middle (MeetITM), the 'effective' security of the above options are reduced as following:

Option 1: 112 bits
Option 2: 80 bits
Option 3: 56 bits

The following table sums it well:
That is the concept of 3 key 3DES and 2 key DES.

Comments

Post a Comment

Popular posts from this blog

Ardilla- New tool for finding SQL Injection and XSS

Three Researchers -- MIT's Adam Kiezun , Stanford's Philip Guo , and Syracuse University's Karthick Jayaraman -- has developed a new tool ' Ardilla ' that automatically finds and exploits SQL injection and cross-site scripting vulnerabilities in Web applications. It creates inputs that pinpoint bugs in Web applications and then generates SQL injection and XSS attacks. But for now Ardilla is for PHP -based Web app only. The researchers say Ardilla found 68 never-before found vulnerabilities in five different PHP applications using the tool -- 23 SQL injection and 45 XSS flaws. More information is awaited. For their attack generation techniques refer to their document at: http://www.cs.washington.edu/homes/mernst/pubs/create-attacks-tr054.pdf
Post a Comment
Read more

File Upload through Null Byte Injection

Sometimes, during file upload we come across situation wherein there would be check on the file extension at the client side as well as server side too. If the application does allow only .jpeg extension to be uploaded, the client side java script checks for the extension of the file before passing the request. We all know that how easily this can be defeated. Some applications, checks for the extension at the server side also. That's not easy to bypass. However there are some ways with which it still can be bypassed. Most of server side scripts are written in high level languages such as Php, Java etc who still use some C/C++ libraries to read the file name and contents. That leads to the problem. In C/C++ a line ends with /00 or which is called Null Byte. So whenever the interpreter sees a null byte at the end of the a string, it stops reading thinking it has reached at the end of the string. This can be used for the bypass. It works for many servers, specially php servers. T
1 comment
Read more

Combining power of Fiddler with Burp

Both are pretty powerful tools when it comes to intercept and modify http communications. But at some point of time, they become even more powerful combo if tied with each other. They complement each other. In a recent pentest I came across a similar situation where in Burp was not able to intercept a specific kind of traffic and Fiddler came to rescue. The application was designed to upload video. The initial communication was straight forward, I mean logging into application, filling up the video details etc. And all these were easily captured by Burp except the point where you hit the Upload Video and it connects to a different server and surprisingly it was not captured by Burp, not sure why, even after repeated attempts. So, I fired Fiddler to see if the it sees this request. But it's a;ways to play with requests using Burp due to it's various functionalities like, Intruder, Repeaters etc. But it was necessary to capture this request in Burp. So the below steps can be
Post a Comment
Read more