Tag Archives: BEAST

TLS/SSL Vulnerabilities

“Which SSL ciphers should I disable?”

A client recently gave me a list of their supported ciphers and asked me which SSL ciphers they should disable – effectively looking for the most secure SSL ciphers they can use. Instead of the fast answer of “disable the insecure¬†ones”, I thought I’d try and write up something useful.

So here’s a handy reference guide I’m working on. This has been time consuming to develop and no doubt will be added to over time. This isn’t intended to be read from start-to-finish, but is more of a handy SSL/TLS issue cheat-sheet.

Continue reading: TLS/SSL Vulnerabilities

What is BEAST?

Browser Exploit Against SSL/TLS

BEAST is an attack against SSL/TLS which is the cryptographic system that protects data sent online. A practical attack was found to be possible against TLS v1.0 and SSLv3.0 (and below). The issue is that the Initialisation Vector (IV) utilised as part of the encryption process can be determined by an attacker. IVs are utilised to prevent encrypted data from being deterministic, they essentially make it harder for attackers to determine patterns in encrypted data. Without them if a repeating pattern is evident in the plaintext then it will be evident in the ciphertext and this type of informations is greatly useful to an attacker. IVs are designed to prevent this, however with the BEAST attack they are shown to be deterministic which greatly reduces their use as a protection mechanism.

It reduces the protection but the deterministic nature is of limited use to an attacker and they are only able to retrieve small amounts of information from the encrypted data, however with attacks against web applications small amounts of data can cause a large impact – if an attacker is able to retrieve information such as session tokens.

Continue reading: What is BEAST?