We propose an efficient commutative group action suitable for non-interactive key exchange in a post-quantum setting. Our construction follows the layout of the Couveignes–Rostovtsev–Stolbunov cryptosystem, but we apply it to supersingular elliptic curves defined over a large prime field $$\mathbb F_p$$ , rather than to ordinary elliptic curves. The Diffie–Hellman scheme resulting from the group action allows for public-key validation at very little cost, runs reasonably fast in practice, and has public keys of only 64 bytes at a conjectured AES-128 security level, matching NIST’s post-quantum security category I.

This paper studies ways to backdoor lattice-based systems following Young and Yung’s work on backdooring RSA and discrete-log based systems. For the NTRU encryption scheme we show how to build a backdoor and to change the system so that each ciphertext leaks information about the plaintext to the owner of the backdoor. For signature schemes the backdoor leaks information about the signing key to the backdoor owner. As in Young and Yung’s work the backdoor uses the freedom that random selections offer in the protocol to hide a secret message encrypted to the backdoor owner. The most interesting and very different part though is how to hide and retrieve the hidden messages.

This paper introduces a high-security post-quantum stateless hash-based signature scheme that signs hundreds of messages per second on a modern 4-core 3.5GHz Intel CPU. Signatures are 41 KB, public keys are 1 KB, and private keys are 1 KB. The signature scheme is designed to provide long-term $$2^{128}$$ security even against attackers equipped with quantum computers. Unlike most hash-based designs, this signature scheme is stateless, allowing it to be a drop-in replacement for current signature schemes.

Censorship-circumvention tools are in an arms race against censors. The censors study all traffic passing into and out of their controlled sphere, and try to disable censorship-circumvention tools without completely shutting down the Internet. Tools aim to shape their traffic patterns to match unblocked programs, so that simple traffic profiling cannot identify the tools within a reasonable number of traces; the censors respond by deploying firewalls with increasingly sophisticated deep-packet inspection. Cryptography hides patterns in user data but does not evade censorship if the censor can recognize patterns in the cryptography itself. In particular, elliptic-curve cryptography often transmits points on known elliptic curves, and those points are easily distinguishable from uniform random strings of bits.

MinimaLT is a new network protocol that provides ubiquitous encryption for maximal confidentiality, including protecting packet headers. MinimaLT provides server and user authentication, extensive Denial-of-Service protections, privacy-preserving IP mobility, and fast key erasure. We describe the protocol, demonstrate its performance relative to TLS and unencrypted TCP/IP, and analyze its protections, including its resilience against DoS attacks. By exploiting the properties of its cryptographic protections, MinimaLT is able to eliminate three way handshakes and thus create connections faster than unencrypted TCP/IP.