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upstream: Turn off finite field (a.k.a modp) Diffie-Hellman key 

exchange in sshd by default. Specifically, this removes the
diffie-hellman-group* and diffie-hellman-group-exchange-* methods. The client
is unchanged and continues to support these methods by default.

Finite field Diffie Hellman is slow and computationally expensive for
the same security level as Elliptic Curve DH or PQ key agreement while
offering no redeeming advantages.

ECDH has been specified for the SSH protocol for 15 years and some
form of ECDH has been the default key exchange in OpenSSH for the last
14 years.

ok markus@

OpenBSD-Commit-ID: 4e238ad480a33312667cc10ae0eb6393abaec8da
This commit is contained in:
djm@openbsd.org 2024-10-06 23:37:17 +00:00 committed by Damien Miller
parent 67a115e7a5
commit 0051381a8c
No known key found for this signature in database
2 changed files with 7 additions and 10 deletions
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8
myproposal.h
View File

@ -1,4 +1,4 @@
/* $OpenBSD: myproposal.h,v 1.73 2024/09/09 02:39:57 djm Exp $ */
/* $OpenBSD: myproposal.h,v 1.74 2024/10/06 23:37:17 djm Exp $ */
/*
* Copyright (c) 2000 Markus Friedl. All rights reserved.
@ -32,14 +32,14 @@
"curve25519-sha256@libssh.org," \
"ecdh-sha2-nistp256," \
"ecdh-sha2-nistp384," \
"ecdh-sha2-nistp521," \
"ecdh-sha2-nistp521" \
#define KEX_CLIENT_KEX KEX_SERVER_KEX "," \
"diffie-hellman-group-exchange-sha256," \
"diffie-hellman-group16-sha512," \
"diffie-hellman-group18-sha512," \
"diffie-hellman-group14-sha256"
#define KEX_CLIENT_KEX KEX_SERVER_KEX
#define KEX_DEFAULT_PK_ALG \
"ssh-ed25519-cert-v01@openssh.com," \
"ecdsa-sha2-nistp256-cert-v01@openssh.com," \

9
sshd_config.5
View File

@ -33,8 +33,8 @@
.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
.\" $OpenBSD: sshd_config.5,v 1.374 2024/09/15 08:27:38 jmc Exp $
.Dd $Mdocdate: September 15 2024 $
.\" $OpenBSD: sshd_config.5,v 1.375 2024/10/06 23:37:17 djm Exp $
.Dd $Mdocdate: October 6 2024 $
.Dt SSHD_CONFIG 5
.Os
.Sh NAME
@ -1062,10 +1062,7 @@ The default is:
sntrup761x25519-sha512,sntrup761x25519-sha512@openssh.com,
mlkem768x25519-sha256,
curve25519-sha256,curve25519-sha256@libssh.org,
ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
diffie-hellman-group-exchange-sha256,
diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,
diffie-hellman-group14-sha256
ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521
.Ed
.Pp
The list of supported key exchange algorithms may also be obtained using