Questions tagged [openssh]

A free and open implementation of the SSH communication security tools.

A free and open implementation of the SSH communication security tools.

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184 questions
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What are ssh-keygen best practices?

Most users would simply type ssh-keygen and accept what they're given by default. But what are the best practices for generating ssh keys with ssh-keygen ? For example: Use -o for the OpenSSH key format rather than the older PEM format (OpenSSH 6.5…
Tom Hale
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Why OpenSSH deprecated DSA keys

There was a question RSA vs. DSA for SSH authentication keys asking which key is better. Basically all answers were more in a favour of RSA over DSA but didn't really tell that DSA would be somehow insecure. Now however DSA was deprecated by OpenSSH…
Petr
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OpenSSH declares ssh-rsa deprecated. What do I do next?

With the 8.2 release of OpenSSH, they have declared that ssh-rsa for SHA-1 will soon be removed from the defaults: Future deprecation notice It is now possible [1] to perform chosen-prefix attacks against the SHA-1 hash algorithm for less than…
Michael come lately
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What is the difference between PEM format to DSA/RSA/ECC? (Might I confuse PEM with these)?

When one creates an ECC SSH key for example, this command can be used: ssh-keygen -o -a 100 -t ed25519 As I understand, the -o argument is used to generate: The private keys using a newer format opposed to the more commonly accepted PEM Are these…
user123574
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2 answers

How exploitable is the recent UseRoaming SSH vulnerability?

I recently heard about a serious bug in an OpenSSH client ( CVE-2016-0777 and CVE-2016-0778 ) that if I understood correctly could cause remote code execution. How difficult would be for an active man-in-the-middle to exploit that?
d33tah
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Is it considered worth it to replace OpenSSH's moduli file?

Consequences of tampered /etc/ssh/moduli describes a possible risk if the moduli file for an OpenSSH server has been tampered with. Taking the logic a step further, is there any concern with the default file shipped with OpenSSH ? I ask because the…
evaryont
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Why did OpenSSH create its own key format, and not use PKCS#8?

Before posting this question about ed25519 , I learned that there are two formats for storing a private ed25519 key, PKCS#8 OpenSSH Format Why did OpenSSH create its own format rather than use PKCS#8? Please include any relevant citations from…
Evan Carroll
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Are there any risks associated with SSH agent forwarding?

I just realized that I need SSH agent forwarding in order to push to one Git server that then forwards the commits to Github.com. I never used SSH agent forwarding and don't understand the security implications of enabling this feature. Do I have to…
d33tah
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How can I convert an ED25519 key in PKCS#8 to OpenSSH private key format?

I'm having a problem where when I export a key from 1password, and use it with ssh -i , I get Load key "/home/user/.ssh/private_ed25519": invalid format Doing a google search on this, it seems to be a problem where 1password stores their ED25519 key…
Evan Carroll
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13
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Does it weaken the encryption of SSH to use compression?

When using compression on openssh (a la ssh -C ... ), does this reduce entropy and make the tunnel traffic more vulnerable to cryptanalysis? Is compression an option I should disable server-side for this or any other reason? I have a vague…
TopherIsSwell
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Why does the result of ssh-keyscan -H contain a header line with the un-hashed server ID?

I'm attempting to build a global known_hosts file for my AWS VPC, and was looking at using ssh-keyscan to acquire the fingerprints of new servers as they are created. The -H option seems sensible, as it means you do not reveal identifying…
IBam
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Is there a list of weak SSH ciphers?

Is there a site, which provides a list of weak cipher suites for (Open-)SSH? I know for example that arcfour is not recommended, but there is a whole list of other cipher suites offered, where I am not quite sure.
skipper
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Copy SSH Public Key from Windows to Ubuntu

I am trying to get my ssh public key from my windows client to ubuntu host, but I have no idea how to. I tried to find the authorized_keys file, but had zero success. ssh-copy-id command did not work from windows. I generated the public/private key…
user15791
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11
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XZ compromise and consequences for people having used it

Here's a hot topic: https://www.redhat.com/en/blog/urgent-security-alert-fedora-41-and-rawhide-users https://lwn.net/Articles/967180/ https://lwn.net/ml/oss-security/20240329155126.kjjfduxw2yrlxgzm@awork3.anarazel.de/ I'm not an expert in reverse…
Artem S. Tashkinov
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Which ssh exploit works by changing the user name in the middle of the process?

Every few hours, I get a few of those in my server logs: sshd[...]: Disconnecting: Change of username or service not allowed: (httpd,ssh-connection) -> (http,ssh-connection) [preauth] sshd[...]: Disconnecting: Change of username or service not…
Heinzi
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