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Questions tagged [openssh]

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

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44 views

OpenSSH v2 Protocol Explanation

I've been searching high and low, trying to find a easily digestible protocol flow of SSH v2. Does anyone have any docs or, could someone give me an example flow? I'm interested in the flow of the ...
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46 views

Risk of committing IdentityFile name for OpenSSH configuration to public repository

What is the risk of committing the IdentityFile line for each of my Host entries in my ~/.ssh/config to my public dotfiles repository? Would providing such information make it any easier for an ...
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64 views

Benefit of using OpenSSH FIDO/U2F support over GPG mode?

OpenSSH version 8.2 introduced support for FIDO/U2F hardware authenticators, via the new public key types "ecdsa-sk" and "ed25519-sk". I currently have SSH authentication set up in combination with ...
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1answer
233 views

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 ...
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24 views

Key Pair permission on Windows 2019

I generated a key pair on Windows Server 2019 using the native ssh-keygen located in System32\OpenSSH. Now I think the permissions of the private key are somewhat worrying... Is it expected to have ...
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72 views

Interpreting SSH information on Windows Event Viewer… sshd: Did not receive identification string from ipaddress on port portnumber

I am currently reading through Windows Event Log (OpenSSH) looking at the artefacts created by an attack, I am trying to understand the meaning of certain notifications. A brute force attack was ...
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1answer
172 views

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 ...
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1answer
53 views

SSH and the ECDH component

With SSH, most of my servers use ed25519 (the twisted Edwards variant EC) for authentication. I was wondering, after authentication with ed25519, does SSH protocol 2 simple use ephemeral/ephemeral ...
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2answers
208 views

How to accept only user identity keys of type ed25519 on OpenSSH Linux server?

I want to force all users to use only ed25519 type keys when logging in via SSH / SFTP to a Linux server which is running a recent version* of OpenSSH. Some general reasons for putting controls on ...
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1answer
86 views

Does `ssh-keyscan` verify the legitimacy of the host(s) it scans?

There are tutorials on the web, such as this one: https://blog.oddbit.com/post/2019-02-24-docker-build-learns-about-secr/ They show you sample code to run ssh-keyscan in an automated manner so that ...
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1answer
37 views

changing defaults when generating new SSH server keys

On Debian, I can generate new SSH server keys: rm /etc/ssh/ssh_host_* dpkg-reconfigure openssh-server but that will generate the keys with default values, ie 2048 RSA key. What is happening under ...
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79 views

SSH (ssh_auth_list) authentication failing from windows to linux

Bit new in ssh and have an issue in understanding. I got a code which uses ssh_auth_list routine as below. method = ssh_auth_list(session); printf(" %d " , method); I am using a ssh library and when ...
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2answers
798 views

Convert ECDSA keys (PEM, OpenSSH)

To work with ECDSA keys I am using the python-ecdsa library. Unfortunately this library can not process keyfiles properly if they are provided in the OpenSSH format. Instead I generate them in the PEM ...
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84 views

How secure is passwordless and keyless SSH login on 127.0.0.1 only, over a secure authenticated tunnel?

I want to use CA signed SSH keys (that would be rotated frequently and have short expiry, ideally centrally managed, all that great stuff). Unfortunately, most of windows GUI tools, such as WinSCP or ...
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106 views

SSH AUTH : sekey vs yubikey vs ssh-keygen

I've been pondering/hacking/experimenting/using/misusing and am torn/puzzled over this for the past month or so; Which of these methods should prove themselves more secure/least susceptible to be ...
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1answer
116 views

Exposure of /etc/ssh, risks?

I accidentally exposed the keys in /etc/ssh What is the risk? I think it will allow someone to impersonate the server and conduct MITM. Will it let someone SSH into the server? I think not because ...
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51 views

Sufficient to only require 2FA for su elevation?

I have a small web-facing server on my home network. It is headless, and the only way to log in is to ssh with pubkey authentication from within the local network. I wanted to turn on a 2FA ...
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47 views

Convert openssl private key to openssh private key [duplicate]

I have an openssl format private key that i need to use as a host key for openssh connection.How can i convert the openssl format private key to openssh formatted private key using ssh-keygen.I have ...
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1answer
100 views

Bruteforcing via port 88 on MacOS

Macos has open port 88 by default. Is it possible to check validity of the password via this port from Linux and how? If the vncserver is active, it is possible to know also the username (by ...
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1answer
240 views

Can a SSH jump host act as MITM?

Let's say, for example, a company has a "centralised" SSH bastion/jump host on an untrusted server (e.g. a virtual machine in "the cloud"). Meanwhile the corporate/customer/whatever network(s) have ...
4
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1answer
124 views

How were attackers able to login to the Apache Foundation's infrastructure over ssh with passwords? (2010)

SSH passwords should not have been enabled for login over the Internet. Although the Infrastructure Team had attempted to configure the sshd daemon to disable password-based logins, having UsePAM yes ...
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1answer
874 views

Loading a passphrase-protected private SSH key from a file with the cryptography Python module

I am trying to load a passphrase-protected private SSH key from a file using the cryptography Python module. However, I'm not exactly sure how to proceed. The following yields a Crypto.Util.Padding....
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1answer
492 views

How do I determine if an existing SSH private key is secure?

For an ordinary user, how would I verify that a private key file was generated using reasonably secure algorithms? In response to things like allegedly insecure ssh-keygen defaults.
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2answers
96 views

Possible to get sshd (openssh) to log the public key of failed key based login attempts?

As I understand sshd (openssh in my case) typically does/may log the fingerprint/hash of the public key of incoming connections which are attempting to authenticate via key. What I'm looking for is ...
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90 views

Could a running SSH server somehow fool connected SSH client to create a reverse port forward?

Let's be extra paranoid and assume that the SSH server my client is connected to, was "enhanced" so that every SSH client that establishes an connection with it, will be tricked into thinking that it ...
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1answer
3k views

Checking if an RSA private key is passphrase protected

I have generated an RSA key-pair on a computer, and I want to check if the RSA private key is encrypted (protected) with a passphrase. Note that the problem is not that I forgot the passphrase, but ...
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2answers
613 views

From FTP to SSH

Currently, I am doing a penetration testing laboratory with a server with the following services: Nmap scan report for 10.0.11.125 Host is up (1.3s latency). Not shown: 998 closed ports PORT STATE ...
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3answers
782 views

Are mkpasswd SHA512 hashes secure for the public?

I am no crypto expert in any way so please bear with me if my question is kind of stupid. We use OpenSSH key pairs on a regular basis and due to the asymmetric nature of key pairs, as far as I ...
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2answers
1k views

For CA-signed ssh keys, how to see various attributes: principals, identity, serial number, options, validity time, etc

I am looking to implement access controls through CA-signed public ssh keys, as described in the article Scalable and secure access with SSH. I am trying to conceive how our security team will manage ...
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1answer
517 views

OpenSSH-server: Are there any security implications and/or value of/for 'TCPKeepAlive yes'

I have read a degree of mixed reports on the security implications and/or value of allowing TCPKeepAlive yes in /etc/ssh/sshd_config (for OpenSSH-server). Anything definitive on the security best ...
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1answer
196 views

Does OpenSSH use padding of random lengths?

According to the end of RFC 4253 § 6, the random padding introduced to each SSH packet is an arbitrary multiple of 8. It mentions that random padding lengths can mitigate traffic analysis: Note ...
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10k views

Any Alternative to Ngrok for constant Connection? [closed]

Im trying to build RAT to test on my computer. I use ngrok for hacking on WAN. But ngrok has a problem of changing its subdomain once the connection is reset. So, I cant use ngrok for hacking over WAN....
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69 views

Concept using ssh to create dynamic firewall. Good or Bad idea?

The Goal Create a secure process to open a firewall port on a server (on demand), start a listening server, and ultimately close the firewall port. This would improve security by not always having a ...
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1answer
107 views

What is the most private option for 2FA with OpenSSH?

When I watch the logs on my server there are always many hundred IP addresses with failed ssh logins. Because fail2ban only slows the attack process down, I decided that I need another solution. ...
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160 views

Why does the openssh-server not use GCM by default?

Well the question is as simple as that . Because I recently noticed that the openssh-server uses AES-CTR for the symmetric encryption and I wondered why ? From what I heared AES-CTR is a block cipher ...
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1k views

What is the general approach to create FIPS compliant SSH?

Please bear in mind that I have no cyber-security background at all, but have been tasked by my company with making certain applications on our platform FIPS-compliant. From what I've discussed with ...
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2answers
14k views

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 ...
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1answer
743 views

what are the disadvantages of running SSH daemon without root?

Is there any risk in running ssh daemon with no root privilege using this method: how-can-i-make-this-daemon-init-run-as-a-non-root-user? Debian Developer's Best Practices for OS Security says the ...
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1answer
174 views

SSH Proxy vs VPN Killswitch

This might be complete nonsense but I've heard people talking about so I'm interested to see if it's valid: I've heard people saying that SOCKS and SSH are more secure/private than a VPN because they ...
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1answer
399 views

SSH and man-in-the-middle

Assume the following scenario and please correct me if I am wrong somewhere: There is a client and there is an SSH server that the client connects to. There is also a man-in-the-middle (MIM) which is ...
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1answer
486 views

Why are SSH host keys stored un-encrypted?

Do we have any standard way to encrypt SSH host keys (like /etc/ssh/ssh_host_rsa_key)? If not, why is it stored in plaintext? Isn't it sensitive information?
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1answer
531 views

Limit on modulus lines in OpenSSH /etc/ssh/moduli file?

I understand that OpenSSH server looks in /etc/ssh/moduli and picks a modulus at random for each Diffie-Hellman group exchange. What I am wondering is whether there is a practical limit on how many ...
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1answer
53 views

Negative consequences of forced encryption of unencrypted secvices

Are there any negative consequences to encrypting an unencrypted service/protocol like FTP, VNC, telnet, and so on by using forced encryption like ssh tunneling or OpenVPN tunnels?
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3answers
338 views

How to prevent sharing SSH private keys by email

Is it possible to prevent the sharing of SSH private keys over email (Outlook, in particular), both within and outside of the organisation?
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2answers
329 views

Security benefit of hardware backed host keys for OpenSSH

There was recently a "two for the price of one" deal on the Yubikey 4 and now I have too many of them. This got me thinking about things to do with them, more or less useful. Of course I already use ...
2
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1answer
57 views

Are the keys generated by ssh-keygen only used in authentication?

After reading SSH Passwordless Login Using SSH Keygen in 5 Easy Steps, I come across the question: Are the keys generated by ssh-keygen only used in login authentication? I mean if I want to modify ...
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226 views

tools for testing ssh packets size [closed]

I need to test maximum-packet-size for SSH protocol. Would be grateful for information on possible tools that can be used for this. What I specifically need is the possibility to indicate packet ...
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3answers
16k views

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 ...
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3answers
3k views

How secure is ssh key-based authentication

I have a newly installed (and updated) Centos 7 server I use for testing. I implemented RSA key based authentication for ssh and set PermitRootLogin to without-password When I logged on this morning ...
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1answer
151 views

How to force openssh client to require both SSH certificate and SSHFP record?

Securely authenticate SSH hosts I have successfully used both OpenSSH Certificates and SSHFP to authenticate hosts when connecting to servers using SSH. But I fail to find a way to require the ...

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