Implement the "sntrup761x25519-sha512@openssh.com" KEX method #498
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This uses a post-quantum key encapsulation method (KEM) to make key exchange future-proof against quantum attacks. It is to be preferred over curve25519-sha256 "when the extra communication size and computational requirements are acceptable."[1] (curve25519-sha256 exchanged 32 bytes where sntrup761x25519-sha512 exchanges 1190 or 1071 bytes.) This KEX method changes the encoding of the key from 'mpint' to 'string'. To make the handling of the K value more uniform, change it to 'string' everywhere, and convert mpints with the high bit set explicitly by prepending a zero byte. Separate the digest from MontgomeryCurve; handle combining curves and hashes (and KEMs) in the BuiltinDHFactories instead. In the BaseBuilder, add "sntrup761x25519-sha512@openssh.com" as first (i.e., preferred) KEX algorithm. [1] https://www.ietf.org/archive/id/draft-josefsson-ntruprime-ssh-02.html
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This uses a post-quantum key encapsulation method (KEM) to make key exchange future-proof against quantum attacks. It is to be preferred over curve25519-sha256 "when the extra communication size and computational requirements are acceptable."[1] (curve25519-sha256 exchanged 32 bytes where sntrup761x25519-sha512 exchanges 1190 or 1071 bytes.)
This KEX method changes the encoding of the key from 'mpint' to 'string'. To make the handling of the K value more uniform, change it to 'string' everywhere, and convert mpints with the high bit set explicitly by prepending a zero byte.
Separate the digest from MontgomeryCurve; handle combining curves and hashes (and KEMs) in the BuiltinDHFactories instead.
In the BaseBuilder, add "sntrup761x25519-sha512@openssh.com" as first (i.e., preferred) KEX algorithm.
[1] https://www.ietf.org/archive/id/draft-josefsson-ntruprime-ssh-02.html