Difference between revisions of "Enable Legacy Cipher in Linux for SecureCRT"
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*Cipher: 3DES | *Cipher: 3DES | ||
*MAC: MD5 | *MAC: MD5 | ||
| − | where used, the client connected to the linux system sshd server (OpenSSH). SecureCRT is actually using the cipher "3des-cbc" specifically. | + | where used, the client connected to the linux system sshd server (OpenSSH). SecureCRT is actually using the cipher "3des-cbc" specifically and "hmac-md5" for the MAC (Message Authentication Codes). |
Supporting legacy ciphers for backwards compatibility is necessary to connect "ssh" with SecureCRT. The ssh server "sshd" ciphers can be configured via the file: | Supporting legacy ciphers for backwards compatibility is necessary to connect "ssh" with SecureCRT. The ssh server "sshd" ciphers can be configured via the file: | ||
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* sshd(8): The default set of ciphers and MACs has been altered to | * sshd(8): The default set of ciphers and MACs has been altered to | ||
| − | + | remove unsafe algorithms. In particular, CBC ciphers and arcfour* | |
| − | + | are disabled by default. | |
| − | + | The full set of algorithms remains available if configured | |
| − | + | explicitly via the Ciphers and MACs sshd_config options. | |
Revision as of 23:26, 26 February 2017
SecureCRT version 3.1.2 has a limited selection of available ciphers. It is an old version of the client. In the past when the selections
- Cipher: 3DES
- MAC: MD5
where used, the client connected to the linux system sshd server (OpenSSH). SecureCRT is actually using the cipher "3des-cbc" specifically and "hmac-md5" for the MAC (Message Authentication Codes).
Supporting legacy ciphers for backwards compatibility is necessary to connect "ssh" with SecureCRT. The ssh server "sshd" ciphers can be configured via the file:
vi /etc/ssh/sshd_config
See what ciphers are available on your system:
ssh -Q cipher localhost
Even though 3des-cbc is enabled in the configuration, the client using 3des-cbc is rejected, as evidence in the log
cat /var/log/auth.log
It turns out that number of version 2 ciphers have been disabled in the 6.7p1-1 release of openssh. Lets see what version of OpenSSH we have.
dpkg-query -l|grep -i openssh
Debian Linux Jessie reports openssh-server 1:6.7p1-5+deb8u3 which has the following ciphers disabled: 3des-cbc,blowfish-cbc,cast128-cbc,arcfour,arcfour128,arcfour256,aes128-cbc,aes192-cbc,aes256-cbc,rijndael-cbc@lysator.liu.se
* sshd(8): The default set of ciphers and MACs has been altered to
remove unsafe algorithms. In particular, CBC ciphers and arcfour*
are disabled by default.
The full set of algorithms remains available if configured
explicitly via the Ciphers and MACs sshd_config options.
