Weak TLS_DH_DSS_WITH_AES_128_CBC_SHA256
- IANA name:
- TLS_DH_DSS_WITH_AES_128_CBC_SHA256
- Hex code:
- 0x00, 0x3E
- TLS Version(s):
- TLS1.2, TLS1.3
- Protocol:
- Transport Layer Security (TLS)
- Key Exchange:
- Diffie-Hellman (DH)
- Authentication:
- Digital Signature Standard (DSS)
- Encryption:
- Advanced Encryption Standard with 128bit key in Cipher Block Chaining mode (AES 128 CBC)
- Hash:
- HMAC Secure Hash Algorithm 256 (SHA256)
- Included in RFC:
- Machine-readable:
- application/json
This key exchange algorithm does not support Perfect Forward Secrecy (PFS) which is recommended, so attackers cannot decrypt the complete communication stream.
The so-called Raccoon Attack affects the specifications of TLS 1.2 and below when using a DH(E) key exchange. According to the researchers, while very hard to exploit, in rare circumstances this timing attack allows attackers to decrypt the connection between users and the server. A fix has been introduced in the TLS 1.3 specification.
In 2013, researchers demonstrated a timing attack against several TLS implementations using the CBC encryption algorithm (see isg.rhul.ac.uk). Additionally, the CBC mode is vulnerable to plain-text attacks in TLS 1.0, SSL 3.0 and lower. A fix has been introduced with TLS 1.2 in form of the GCM mode which is not vulnerable to the BEAST attack. GCM should be preferred over CBC.