SSL/TLS Pentesting: What are Cipher Suites

One of the main functions of the SSL/TLS protocols is to allow the client and server to negotiate a mutually acceptable "cipher suite" to use for the connection. The cipher suite chosen specifies a set of algorithms which the client and server will use to perform key exchange, encryption, and message authentication.
A cipher suite is typically described in a format similar to this:
TLS_RSA_WITH_AES_128_CBC_SHA
where RSA is the key exchange algorithm, AES_128_CBC is the encryption cipher (AES using a 128-bit key operating in Cipher-Block Chaining mode), and SHA is the Message Authentication Code (MAC) algorithm.
The cipher suites a server is configured to support should be dictated by its security requirements. The following guidelines are generally recommended as a baseline:
The key exchange algorithm should be restricted to those which provide "perfect forward secrecy", such as Ephemeral Diffie-Hellman (DHE) or Ephemeral Elliptic Curve Diffie-Hellman (ECDHE).
The cipher should not suffer from known cryptanalytic flaws. This rules out RC4 which has been known to have flaws for many years and in the past few years has been shown to be significantly weaker than originally thought.
The cipher should use at least a 128 bit key (which rules out DES and Triple-DES).
Cipher-Block Chaining (CBC) mode is prone to padding oracle attacks and should ideally be avoided altogether, but specifically it should not be used in conjunction with SSLv3 or TLSv1.0 as this can lead to vulnerability to the BEAST attack. An alternative is Galois Counter Mode (GCM) which is not affected by these problems and offers authenticated encryption.
The message authentication algorithm should ideally be SHA256. MD5 is known to be cryptographically weak and should be avoided, and SHA1 (just denoted SHA in the cipher suite specifications) has its own weaknesses which place attacks within the realm of possibility.

For all three algorithms, the NULL / anon setting should be avoided as these provide no security at all. "Export" algorithms should also be disabled as their short key lengths make them susceptible to brute-force attacks and other attacks such as the FREAK attack.

Nmap's "ssl-enum-ciphers" script can be used to produce a list of the supported cipher suites
command : nmap --script ssl-enum-ciphers -p 443 example.com
the out put will look like the below image

Stay tuned 

Special Thanks 
Sooraj Shekhar

Team Computer Korner

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