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Old 10-02-2018, 11:48 AM
bgagnon bgagnon is offline
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Question FAQ: What causes the "No compatible key-exchange method" error in SecureCRT?

If you are getting some form of the below error:
Key exchange failed.
No compatible key-exchange method.
The server supports these methods: 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,diffie-hellman-group14


You can turn on Trace Options output (File menu) and find this info:
Code:
[LOCAL] : Available Remote Kex Methods = 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,diffie-hellman-group14-sha1 
[LOCAL] : Selected Kex Method = ecdh-sha2-nistp521


KEX or Key Exchange methods: In SecureCRT, configurable in the Connection / SSH2 category of Session Options.
As of v8.5.3, support for curve25519-sha256 and curve25519-sha256@libssh.org key exchange algorithms has been implemented.

As of version 8.5.1, current Key Exchange algorithms supported are (with version when support was first added):
ecdh-sha2-nistp521 (v7.3.x)
ecdh-sha2-nistp384 (v7.3.x)
ecdh-sha2-nistp256 (v7.3.x)
diffie-hellman-group-exchange-sha256 (v7.3.x)
diffie-hellman-group14 (v5.0.x)
diffie-hellman-group (v3.0.x)
Kerberos (v3.0.x)
Kerberos (Group Exchange) (v3.0.x)

Note that while diffie-hellman is still available, it was disabled as of v8.0 due to well-documented flaws in the algorithm associated with news surrounding the Logjam vulnerability. Many other SSH servers and clients have turned off default support for the diffie-hellman key exchange algorithm.

Changes in SecureCRT 8.0 (Beta 1) -- January 28, 2016 (8.0.0.1011)
-----------------------------------------------------------------------------------
Changes:
  • SSH2: The "diffie-hellman" key exchange algorithm is off for the default session. This change only affects new installations.


You can employ the power of editing the Default session to enable any new key-exchange algorithms in all of your existing and future sessions. Here are some links to a tip and a video that provide more details about using the Default session to make mass changes to multiple sessions:
https://www.vandyke.com/support/tips/defaultset.html
https://www.youtube.com/watch?v=5RbuZn9L48g
Note: In order for a "change" to be applied to all other sessions, the Default session's option/field you're targeting must actually be modified/different from its current value.
Attached Images
File Type: png SCRT851_altered_key_ex_category.png (43.3 KB, 2083 views)
File Type: png line.png (522 Bytes, 5670 views)
File Type: png key_ex_error_in_SCRT.png (29.0 KB, 2205 views)
__________________
Thanks,
--Brenda

VanDyke Software
Technical Support
support@vandyke.com
(505) 332-5730

Last edited by bgagnon; 03-01-2019 at 09:18 AM. Reason: Update regarding curve (and removed URL formatting where algo referenced)
  #2  
Old 11-28-2018, 01:57 PM
bgagnon bgagnon is offline
VanDyke Technical Support
 
Join Date: Oct 2008
Posts: 3,937
Update

Hi All,

Good News!

Our developers have implemented support for the curve25519-sha256 key exchange algorithm (known by two names, curve25519-sha256 and curve25519-sha256@libssh.org, it's the same algorithm in both cases).

If you would like us to make this pre-release build available to you, please contact support@vandyke.com and include "Curve25519 feature request" (or similar) in the subject line. If writing us from an email address other than that associated with your VanDyke Software download account, then please indicate in the body of the email what email address is associated with your download account.
__________________
Thanks,
--Brenda

VanDyke Software
Technical Support
support@vandyke.com
(505) 332-5730
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Tags
curve , debugging , diffie-hellman , ecdh , faq , kex , keyex , securecrt , securefx , troubleshooting


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