SSH (Secure shell) is a protocol for secure communication between computers to execute remote commands, transfer data and tunnel TCP connections.

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Secure Configuration of Ciphers/MACs/Kex available in SSH

Following on the heels of the previously posted question here, Taxonomy of Ciphers/MACs/Kex available in SSH?, I need some help to obtain the following design goals: Disable any 96-bit HMAC ...
6
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2answers
3k views

Best way to allow sudo access when using ssh keys

Probably a simple question, but I can't seem to find any actual best practices out there. I manage a handful of servers and I am really getting sick of tracking my passwords in pwsafe. I've been ...
3
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2answers
356 views

Plausibly deniable SSH - does it make sense?

My colleague just told me he can't make outbound SSH connections in his corporate networks, so I advised him to set up a server on 443 port and it worked. I then started thinking that the ...
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1answer
647 views

Afraid about SSH on my Linux system

I've checked my Linux server (Centos 6) with rkhunter. I found the following in rkhunter log [14:38:54] Checking if SSH protocol v1 is allowed [ Warning ] [14:38:54] Warning: The SSH ...
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3answers
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SSH key-type, rsa, dsa, ecdsa, are there easy answers for which to choose when?

As someone who knows little about cryptography, I wonder about the choice I make when creating ssh-keys. ssh-keygen -t type, where type is either of dsa,rsa and ecdsa. Googling can give some ...
1
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1answer
235 views

SSH authorized_keys

Can you correct me on this. I create a keypair on my PC. Copy the public key (append to authorized_keys) on the server. Disable password auth on the server, and SSH to server from my PC. I have ...
8
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3answers
362 views

Why is RFC4255 (SSHFP) not used for https?

I had this idea a few hours ago, but of course it already exists and there is even an RFC... Why don't we publish the fingerprint for the SSL/TLS certificate via DNS? We need DNSSEC to make sure the ...
1
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1answer
86 views

Securing WebHosting Shell Access

If I provide SSH access to users who has paid webhosting service, what security measures should be applied ? What I can think of: SSH keys RSA of 4096 size (shall be secure for a while) Apache ...
9
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2answers
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How do I get the RSA bit length with the pubkey and openssl?

I have a public key generated with ssh-keygen and I'm just wondering how I get information on the keylength with openssl?
2
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1answer
3k views

What effect has MaxAuthTries=1?

I configure a new server right now and ask myself what is the internally effect if I set MaxAuthTries=1 in sshd_config. The server only accept key authentication an no root logins. Has this setting ...
0
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3answers
131 views

Securely transferring data from service provider to client

Suppose a client C wants to transfer form a service provider P, who collected data on behave of C using a web-application. Additionally, suppose the amount of data is larger than 100 MByte and ...
6
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1answer
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Consequences of tampered /etc/ssh/moduli

What are the consequences if an attacker is able to modify the /etc/ssh/moduli file?
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0answers
132 views

Why my proxy is still having some connections blocked

I am behind a firewall in France. I connect to proxy A, in Ireland with Dante via SSH port 22 and make a tunnel forwarding port 1080. The proxy works as expected but still having a port range ...
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4answers
416 views

Is a short sudo password ok?

On a server I control, I have disabled password logins (public key only), but still need to enter my password to access sudo. This is becoming cumbersome, as I use a long, automatically generated ...
7
votes
3answers
997 views

Are duplicate SSH server host keys a problem?

I'm doing an assessment of a small network that is using a good bit of virtualization. They have cloned some of their linux machines after generating their SSH server host keys. So the servers all ...
8
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5answers
5k views

What are the ways to implement two factor authentication?

We have devices that can generate tokens. So we can use tokens with passwords to perform two factor authentication. There are many ways to implement such systems to enhance security. One of two I ...
8
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3answers
5k views

What is the best practice: separate ssh-key per host and user VS one ssh-key for all hosts?

Is it better to create a separate ssh-key for each host and user or just using the id_rsa key for all host to authenticate? Could one id_rsa be a malpractice for the privacy/anonymity policies? ...
12
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1answer
3k views

Is it safe to disable SSH host key checking if key-based authentication is used?

I have some tasks that go like so: Spin up some new EC2 instances (Amazon Web Services) Get them to execute a task Kill them The problem is that they're (seemingly) randomly assigned an IP ...
7
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2answers
916 views

Does ssh-agent store the SSH key passwords in cleartext in the memory?

So what is the use of protecting the ssh key with password when the notebook has full disk encryption? If someone is able to get the id_rsa then it is able with no effort (?) to get the id_rsa's ...
5
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2answers
1k views

What's the modp length of diffie-hellman-group-exchange-sha256?

OpenSSH 6.2 offers the following key exchange algorithms by default ecdh-sha2-nistp256 ecdh-sha2-nistp384 ecdh-sha2-nistp521 diffie-hellman-group-exchange-sha256 diffie-hellman-group-exchange-sha1 ...
7
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3answers
249 views

Is it dangerous to place ~/ssh/config on GitHub?

I am used to version control most of my dot files and push them to a repository on GitHub. I would also like to add ~/.ssh/config to have an up-to-date configuration on all machines. Could an ...
6
votes
1answer
215 views

SFTP or FTPS for connecting to a VPS?

I'm going to be hosting one of my websites on a VPS soon and I want to make it as secure as possible. Only I will need access to the VPS, and I can't see that changing in the near future. Because it ...
5
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3answers
5k views

How does storing GPG/SSH private keys on smart cards compare to plain USB drives?

I have a basic understanding of private/public key cryptography and have been using it for SSH logins and GPG encryption/signing for a while now. However, I have always kept the private key/keyrings ...
3
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1answer
1k views

How to remove ssh rootkits? [duplicate]

I checked my linux server with rkhunter, I got following warning messages, ... [00:35:35] Found file '/usr/include/gpm2.h'. Possible rootkit: Trojaned SSH daemon [00:35:35] ...
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4answers
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How to use public WiFi safely?

The Dangers of Open Wi-Fi How does one go about sending valuable information (for example inputting email username and password) over a free password-less public WiFi network? The only option that I ...
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1answer
265 views

Can I develop an SSH client for iPad in Sweden and sell it in Apple App Store? [closed]

I wonder, if I am allowed to develop an SSH client for distribution through Apple App Store without breaking any export regulations? I don't really know much about the encryption algorithm. Below is a ...
11
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1answer
315 views

What are the risks of SSHing to an untrusted host?

When SSHing to a host that has been compromised (or outright replaced using the stolen server keys) by an attacker with root permissions, what is the worst that can happen to the client? It is well ...
3
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2answers
680 views

How to secure a truecrypt container allowing access with multiple SSH public keys?

I would like to create a TrueCrypt container which can be accessed by multiple people. The container itself can be stored anywhere, e.g. in a shared folder in Dropbox or Google Drive, ... I would ...
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1answer
244 views

Rsync without ssh access [closed]

There is a host of computers and one of them needs to Rsync a specific folder from each of the other computers. The way its done right now is that this central computer has ssh access to all those ...
5
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3answers
364 views

How I can prove that SSH attacks are not from my application?

My ruby on rails web application is hosted on Linode. Linode opened a ticket and blamed my Linode server for attacking other servers. The logs revealed that it's a SSH brute force attack which ...
2
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1answer
970 views

SSH says Authentication tried for XX with correct key but not from a permitted host

I am using and authorized_hosts file to authorise certain keys. One of those is restricted with the prefix from="1.2.3.4", the others are valid from anywhere. When accessing from a machine that has ...
4
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3answers
233 views

Storing config securely in a semi trusted shared hosting environment

I'm looking for a pattern to store a config file containing sensitive information in a semi trusted hosting environment. Semi trusted in this case meaning I trust them in general, but not with this ...
3
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2answers
384 views

any reason not to run tmux/wemux on a bastion host?

Is there any reason to worry about running tmux/wemux on a bastion host? It seems to me that it would open up vectors to have your terminal sessions hijacked by some locally exploited account on the ...
0
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1answer
834 views

Does ssh-keyscan tell you if a server supports RSA or DSA keys?

A question came up on the Unix & Linux SE site: Checking if passwordless ssh authorization is possible without permission for sshd_config?. I immediately thought you could possibly infer this ...
1
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1answer
151 views

Simple and secure remote installation method that accepts input via a web page?

When installing software on a remote server: Is it possible to let the admin (i.e. the user that installs the software) define admin username and password via a HTML page, in a secure manner? ...
2
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1answer
730 views

What is the actual value of disabling remote root login using ssh?

I have read the answers regarding why you should disable remote root login, but there is something nagging me. Assume this: Scenario 1: Remote server A. Remote root login disabled. Password ...
2
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1answer
167 views

SSH Protocol classification version exchange messages

I am trying to classify network protocols over network traffic . Now my task is SSH protocol. I read the RFC and know SSH starts with protocol exchange message from both client and server . Format ...
7
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1answer
217 views

Using / finding covert channels in inter-process communication

I've got a class exercise that involves a virtual game of Werewolves/Mafia. We're not really taught how to do anything in this class, which makes it hard for everyone to do the labs. The idea is that ...
1
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1answer
2k views

Vulnerability by leaving an open port in a pc

I have the following set-up. Home pc ---reverse ssh tunnel---> to linux server The reverse ssh tunnel is set-up so that on my home pc, port 22 is open, but I have nothing currently listening on that ...
4
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1answer
123 views

GPG warns about unprotected subkeys while using monkeysphere

Issuing monkeysphere subkey-to-shh-agent GPG warns me: gpg: about to export an unprotected subkey then it asks for the passphrase and everything works fine. What's the meaning of "export an ...
5
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2answers
1k views

Linux forensics questions (ssh config, user activity)

I'm a linux noob and have an assignment I'm a bit stumped on... We're given VirtualBox (vdi) images and raw files for the state of a linux server at 3 different dates. We're supposed to answer: ...
3
votes
3answers
1k views

Using /usr/bin/passwd as login shell

I have a requirement to set up a SSH tunnel between two hosts. SSH server runs on a Linux host, and the SSH client (PuTTY) runs on a Windows host. I have set up a separate user account (say 'tunnel') ...
1
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1answer
393 views

Custom Python Server - how to secure it?

I'm going to purchase my own dedicated server service soon and run few python server scripts on it. Firstly, let me tell you that I am total noob when it comes to internet security and was unable to ...
5
votes
3answers
1k views

What is the difference between encrypted data and data sent through an encrypted tunnel

I am looking at different VPN protocols. [1] L2TP does not provide encryption so require IPSec to encrypt the data [2] IPSec tunnel provide encryption to the tunnel What is the difference in terms ...
37
votes
4answers
5k views

Should I change the default SSH port on linux servers?

Is there any advantage in changing the SSH port, I've seen people do that, but I can't seem to find the reason why. If you have a strong password and/or a certificate, is it useful for anything? ...
3
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1answer
3k views

What is the difference between RSA1 & RSA in regards to SSH? Also when is the fingerprint & random art used?

I have searched this site for RSA1 with no results. From multiple google searches I have understood that RSA1 was used in SSH1 (which isn't recommended). However if its a single algorithm why are ...
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2answers
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What is the “openssh-blacklist” package? Is it related to the Debian OpenSSL bug?

What is the "openssh-blacklist" package? Is it related to the Debians OpenSSL bug?
7
votes
1answer
2k views

Is it secure to transfer an RSA public key by email?

I've set up my VPS'ssh server to accept only key-based identification: I disabled password-based connection. As a consequence I am connecting from home with an RSA key generated prior to password ...
0
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1answer
4k views

Dropbear SSH server use-after-free vulnerability

"This vulnerability is located within the Dropbear daemon and occurs due to the way the server manages channels concurrency. A specially crafted request can trigger a use after free condition which ...
0
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3answers
184 views

Make the public key unrecoverable given the private key

OpenSSL seems to bundle the private key together with the public key when it produces .pem files. Is there a way to prevent this from happening; i.e. prevent OpenSSL from creating a .pem private key ...