OpenSSH 9 protects against attacks from future quantum machines • The Register

OpenSSH 9 is here, with updates aimed at handling cryptographically challenging quantum computers.

The popular open source SSH implementation aims to provide secure communication in potentially insecure network environments. While version 9 is ostensibly focused on bug fixes, there are a few substantial changes that might catch the unwary, including the switch from legacy SCP/RCP to SFTP by default.

The OpenSSH group warned that the change would arrive earlier this year, with a deprecation notice in February’s 8.9 release. Experimental support for transfers using SFTP as a replacement for SCP/RCP appeared in version 8.7 in August 2021 with the warning: “SFTP is planned to become the default transfer mode in the near future” .

The future, it seems, has arrived (at least as far as OpenSSH is concerned) with the default move to SFTP, which introduces some potential incompatibilities: the “capricious and flimsy quote” requirement used by the old SCP/RCP is over. and attempts to use it may cause transfers to fail,” according to the OpenSSH group, which added that there was no intention to introduce bug compatibility for the old SCP/RCP when updating. using SFTP (although the -O flag can be used to force scp to use the legacy protocol.)

Hello from the future-ture-ture

However, a bigger nod to the future came in the form of using the “default Streamline NTRU Prime + x25519 hybrid key exchange method”.

“The NTRU algorithm is believed to be resistant to attacks enabled by future quantum computers,” the team explained, “and is paired with the X25519 ECDH key exchange (the previous default) as a bulwark against any weakness. of NTRU Prime that might be discovered in the Combination ensures that the hybrid exchange offers at least as good a security as the status quo.”

He added: “We are making this change now (i.e. before cryptographically relevant quantum computers) to prevent ‘capture now, decrypt later’ attacks where an adversary capable of recording and storing the ciphertext of the SSH session would be able to decipher it once a sufficiently advanced quantum computer is available.”


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Nth degree truncated polynomial ring units (NTRUs) are a cryptographic system and a contender for secure communication should quantum computers ever appear in the real world.

OpenSSH clearly thinks they are on the right track, as are other organizations; The US National Science Foundation awarded a $715,000 grant to researchers to research gaps in quantum computing security, although last year the US National Security Agency said it ” it is unclear when or even if a quantum computer of sufficient size and power to exploit public-key cryptography (a CRQC) will exist.”

The OpenSSH team’s decision may therefore be prudent. After all, who knows what the future holds? ®