30 Dec 2021
Bulletproof TLS Newsletter is a free periodic newsletter bringing you commentary and news surrounding SSL/TLS and Internet PKI, designed to keep you informed about the latest developments in this space. Received monthly by more than 50,000 subscribers. Written by Hanno Böck.
A new RFC officially deprecates the use of the MD5 and SHA-1 weak hash algorithms in TLS handshake messages. The deprecation of these old hash algorithms has a long history, dating back to research results from sixteen years ago.
In 2008, researchers were able to use the weakness in MD5 to create a rogue CA certificate. But that attack relied on a number of conditions; notably, the CA used nonrandom serial numbers, which are no longer used by CAs today. Nevertheless, the attack showed the dangers of weak hash functions, and in the web PKI system, both MD5 and SHA-1 certificates have been deprecated.
However, signatures within the TLS handshake also use these hash functions. In 2015, researchers analyzed how weak hash functions in TLS can be attacked, in a method known as the SLOTH attack.
In the latest TLS version, 1.3, MD5 and SHA-1 are forbidden, but TLS 1.2 and earlier still allowed these weak hash functions. The new RFC now states that MD5 and SHA-1 must not be used any longer for signatures in the TLS handshake.
The old hash functions can still be used in HMAC as this is not affected by collision attacks. But HMAC-based TLS ciphers are also being phased out for other reasons—notably, padding oracle attacks.
This subscription is just for the newsletter; we won't send you anything else.
Here is an interesting job we've come across in the last month:
If you know of similar jobs that our readers might be interested in, for example cryptography, TLS, or PKI, let us know and we may add them to future newsletters.
And here are some resources that you might find useful:
Designed by Ivan Ristić, the author of SSL Labs, Bulletproof TLS and PKI, and Hardenize, our course covers everything you need to know to deploy secure servers and encrypted web applications.
Remote and trainer-led, with small classes and a choice of timezones.
Join over 2,000 students who have benefited from more than a decade of deep TLS and PKI expertise.