Lucky13

Lucky13 is a potential vulnerability when using cipher block chaining (CBC) ciphers with TLS. The attacks arise from a flaw in the TLS specification rather than as a bug in specific implementations. The vulnerability comes in the form of a timing attack on the TLS MAC calculation. The TLS MAC calculation includes 13 bytes of header information (5 bytes of TLS header plus 8 bytes of TLS sequence number) and that's why it is called Lucky 13.