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https://issues.apache.org/jira/browse/SSHD-704?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17134990#comment-17134990
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Matt Sicker commented on SSHD-704:
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Though from a theoretical point of view, since there's already an EdDSA library 
dependency that implements Edwards curves as in Ed25519 signatures, there's a 
formula to convert Montgomery curves used in X25519 back and forth to their 
corresponding Edwards curves.

Let {{p = 2^255 - 19}} and {{A = 486662}}. The Montgomery curve in X25519 is 
the formula {{y^2 = x^3 + A*x^2 + x}} modulo {{p}} (i.e., over the finite prime 
field). That's isomorphic to the Edwards curve with {{d = 1 - 1/121666}} in the 
formula {{x^2 + y^2 = 1 + d*x^2*y^2}} modulo {{p}}. This allows implementers to 
use either the Montgomery curve or the Edwards curve for calculations involving 
either protocol (sounds handy for embedded platforms).

Source: https://cr.yp.to/newelliptic/nistecc-20160106.pdf section 4

> Add support for curve25519-sha...@libssh.org  key exchange
> ----------------------------------------------------------
>
>                 Key: SSHD-704
>                 URL: https://issues.apache.org/jira/browse/SSHD-704
>             Project: MINA SSHD
>          Issue Type: Improvement
>    Affects Versions: 1.4.0
>            Reporter: Lyor Goldstein
>            Priority: Major
>              Labels: features
>         Attachments: Curve25519.java, Curve25519SHA256AbstractDH.java, 
> Curve25519SHA256DHFactory.java, Curve25519SHA256KeyExchange.java, 
> Curve25519SHA256KeyExchangeFactory.java
>
>
> See
> * [curve25519-sha...@libssh.org kexy exchange 
> specification|https://git.libssh.org/projects/libssh.git/tree/doc/curve25519-sha...@libssh.org.txt]
> * [Secure Shell (SSH) Key Exchange Method using Curve25519 and 
> Curve448|https://tools.ietf.org/html/draft-ietf-curdle-ssh-curves-06]
> * [JEP 324: Key Agreement with Curve25519 and 
> Curve448|http://openjdk.java.net/jeps/324]



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