Block and Stream Ciphers

Symmetric Encryption Techniques – Block and Stream Ciphers.

Symmetric Encryption Techniques - Block and Stream ciphers

Two types of symmetric encryption techniques that are used are Block and Stream Ciphers, in this post I will cover them both in a high level comparison.

Block Ciphers

Block ciphers take a section of plaintext (a block) and turns them into block of ciphertext of 64 or 128 bits. The block size is how much data is encrypted in one go.

The output from a block cipher is usually larger than the input data, due to the ciphertext being a multiple of the orginal block size.

Common modes of operation block ciphers are Cipher Block Chaining (CBC) and Electronic Codebook (ECB).  Block ciphers include DES with a 64-bit block size and AES with a 128-bit block size.

Stream Ciphers

Stream ciphers encrypt plaintext one byte or one bit at a time, as opposed to a block of data at a time  as with a block cipher. With a stream cipher, the conversion of these smaller plaintext sections of data can vary, depending on when they are viewed during the encryption process. Stream ciphers can be much faster than block ciphers, and usually do not increase the message size, because they can encrypt an any specific number of bits.

Stream ciphers include RC4 (and the RC series) ciphers. DES can also be used in stream cipher mode.

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Quick SSL Scan

OK so with a my new website up my first thought was ‘right lets secure it!’. Now if only more people thought this way surely we wouldn’t see half the info sec issues we see today. So I’m probably slightly biased on the subject being a Pentester. Not sure if biased or paranoid is better word.

I’m supposed to be on holiday in wales for the bank holiday however 8 hours into the site build and can’t help but think, security. A few tasks later and I navigate to Qualys, lets see where we currently stand, 10 minuets later and I’m building a Kali 2.0 virtual machine in Virtual Box on my laptop in the hopes of pentesting it over 3G!

So a Grade B on ssllabs.com . A little work needed I think.

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Qualys.com is a great resource for scanning URL’s to see what SSL/TLS cipher suites are in use. Check it out!

Disabling SSL v2, v3 and also RC4 in Apache2.

By the time I had finished typing this post I was up to a A- having disabled RC4 in the SSL.conf file in mods-enabled folder be appending the ‘SSLCipherSuite’ with :!RC4. Disabling SSL v2 and v3 is also a simple step by appending the ‘SSLProtocol’ line with ‘-SSLv3 -SSLv2’ in the same file.

This is very much only a small step towards securing a site, although a good start!

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