Weakdh.org Website Review

popular cryptographic algorithm that allows Internet protocols to agree on a shared key and negotiate a secure connection. It is fundamental to many protocols including HTTPS, SSH, IPsec, SMTPS, and protocols that rely on TLS. We have uncovered several weaknesses in how Diffie-Hellman key exchange has been deployed: LOGJAM ATTACK AGAINST THE TLS PROTOCOL. The Logjam attack allows a man-in-the-middle attacker to downgrade vulnerable TLS connections to 512-bit export-grade cryptography. This allows the attacker to read and modify any data pas*ed over the connection. The attack is vulnerability, and attacks a Diffie-Hellman key exchange rather than an RSA key exchange. The attack affects any server that supports THREATS FROM STATE-LEVEL ADVERSARIES. Millions of HTTPS, SSH, and VPN servers all use the same prime numbers for Diffie-Hellman key exchange. Practitioners believed this was safe as long as new key exchange messages were generated for every connection. However, the first step in the number field sieve—the most efficient algorithm for breaking a Diffie-Hellman connection—is dependent only on this prime. After this first step, an attacker can quickly break individual connections. We carried out this computation against the most common 512-bit prime used for TLS and demonstrate that the Logjam attack can be used to that a nation-state can break a 1024-bit prime. Breaking the single, most common 1024-bit prime used by web servers would allow pas*ive eavesdropping on connections to 18% of the Top 1 Million HTTPS domains. A second prime would allow pas*ive decryption of connections to 66% of VPN servers and 26% of SSH servers. A close reading of published NSA leaks shows that the agency's attacks on VPNs are David Adrian, Karthikeyan Bhargavan, Zakir Durumeric, Pierrick Gaudry, Matthew Green, J. Alex Halderman, Nadia Heninger, Drew Springall, Emmanuel Thomé, Luke Valenta, Benjamin VanderSloot, Eric Wustrow, Santiago Zanella-Béguelin, and Paul Zimmermann