You may have recently noticed that Nimbusec generates new types of TLS alerts. This is because we’ve expanded the list of insecure or not recommended protocols and cipher algorithms.
First, we now issue a yellow alert when the TLS 1.0 protocol is used. We chose the warning because since 30 June 2018 it is necessary to deactivate TLS 1.0 in order to meet the PCI Data Security Standard (PCI DSS) for safeguarding payment data.
Further, we improved testing if weak cipher suites can be used by checking for OpenSSL LOW ciphers. The LOW configuration summarizes low strength encryption cipher suites, using only 64 or 56 bit encryption. Since OpenSSL 1.0.2g, these ciphers are disabled in default builds.
One of such low strength encryption cipher suites is IDEA, where we now also issue a warning when it is not deactivated in the configuration. IDEA uses 64-bit blocks for encryption, which is considered as weak. Per RFC5469 this cipher is deprecated and has been completely removed in TLS 1.2.
Another cipher suite that we now flag with a yellow alert, if it is not deactivated, is the SEED cipher suite. SEED is an older South Korean cipher. OWASP recommends to not use it anymore so we introduced this warning to match the OWASP recommendations.
Finally, we now issue a red alert if a SHA1 certificate is found in the certificate trust chain. SHA1 certificates are already flagged as insecure by all major web browsers since 2017. After a few days of alerting all SHA1 certificates in the trust chain, we now make sure that root certificates using SHA1 signatures are excluded.