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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Attract Brute Force SSH Attacks

I posted a question on Server Fault, but got downvoted and had the question closed. One of the comments suggested looking over here, so here goes: For my senior project, I'm working on an ...
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how safe is a home NAS with ssh access?

I'm thinking about acquiring a NAS from Synology (or QNap), these are pretty cool NAS and do much more than just storing files. Some extras include: ssh, ftp, telnet, mail servers photo gallery ...
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How to regain access to the server?

I have a Debian server with KVM available 24/7. It was recently broken into and its root password changed. My hosting provider has restored my access and helped me change the password. But in the ...
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Disabling authentication via DSA keys in OpenSSH?

How can I disable DSA and ECDSA authentication on my server with OpenSSH 5.9? Sifting through the documentation material and doing a web search didn't yield any results - only an old bug report for ...
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1answer
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What are the differences between the arcfour, arcfour128 and arcfour256 ciphers in OpenSSH?

What are the differences between the arcfour, arcfour128 and arcfour256 ciphers in OpenSSH? I am interested about: speed and security implications. I know that arcfour is fast for file transfers, ...
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Implementing Secure Remote Password with Remote Desktop Application

I had read the Secure Remote Password Protocol paper written by Tom Wu. This protocol is resistant to dictionary attacks. I have also go through some papers regarding to VNC attacks due to weak ...
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2answers
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Attacks in SSL and SSH

Assume that we have two end-host A and B connected by two routers R1 and R2. A wants to send a large file to B. A decides to establish SSH connection with host B using public key authentication. ...
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195 views

Why CAs instead of global fingerprint database?

Why do we use "too big to fail" CAs and the chain of trust instead of a global fingerprint database in a similar vein to how ssh works?
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Can I develop SSH-based tools within United States?

It is well known that development of open-source cryptographic tools is very problematic within the United States: all open-source ssh-based software was specifically developed outside of the US of A ...
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OpenSSH default/preferred ciphers, hash, etc for SSH2

When using OpenSSH server (sshd) and client (ssh), what are all of the default / program preferred ciphers, hash, etc. (security related) and their default options (such as key length)? So, what are ...
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Which SSH security is stronger? 2 Factor or Public key

For SSH authentication, which is more secure? 2 Factor Authentication using a USB token/Google Authenticator(time based) OR Public/private key with password Or could they be both used at the same ...
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length of ciphers versus length of key

ssh-keygen defaults to RSA (for SSH protocol 2) and a 2048 bit key. At this description of ssh The supported ciphers are: 3des-cbc, aes128-cbc, aes192-cbc, aes256-cbc, aes128-ctr, ...
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Brute-force an SSH-login that has only a 4-letter password

Suppose, you know that a certain computer is only protected by such a short password, then you could just try every possible combination easily. How would a script look like, that tries to crack that ...
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4answers
540 views

I think my server is under attack, what can I do to stop it? [duplicate]

Possible Duplicate: Invalid users trying to log in to my server I have a small ssh server mostly used for file sharing. A couple of other people and I use it and there are only 3 users. ...
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Vulnerabilities of Secure Shells

I ssh into my school's engineering computer to submit large programmin projects on a regular basis. Are there any vulnerabilities or worries about using this channel so frequently? What makes a secure ...
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1answer
359 views

What are some steps to take for securing a Linux server that aren't in this list of obvious ones?

Obvious things: Disable root login (rather, don't enable it) Secure SSH (no root login, key auth only, timeout after inactivity, whitelist users who can SSH in, etc.) IP Tables firewall whitelisting ...
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1answer
292 views

SSH Log: “Accepted password for user…”

I have only port 29999 open for SSH connections. But in the log file I see entries like this: Accepted password for user1 from 190.101.200.100 port 55805 ssh2 saying that a connection was accepted ...
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Improve SSH logs

I want to improve my SSH log. I would like to basically be able to see failed attempts with ip address and the password used. is that possible? Right now I see something like this: Failed password ...
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3answers
319 views

Petraeus scandal - what would have been a better way to communicate electronically [closed]

Not a security professional here but .... having read through how it happened, it's clear sending these emails from the shared account by Paula Broadwell was the problem (if I understand correctly). ...
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1answer
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How to restrict SSH access outside of LAN? [closed]

We have several dedicated servers. We need to ensure "root" user can not be accessible through SSH outside of LAN. I have searched and found the followings # ...
3
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1answer
974 views

Replacing weak SSH fingerprint algorithms

Even though MD5 has been broken for years and its vulnerabilities have been used to create real-world rogue X.509 CAs and other horrible things, OpenSSH and PuTTY still use MD5 as the default public ...
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2answers
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How to correctly secure a ssh session against MITM attack?

How do you improve the security of your ssh session against a man-in-the-middle attack?
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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 ...
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1answer
240 views

Is the `ssh-agent`'s DSA signature deterministic?

In my hopes to use ssh-agent to generate a signature as password I implicitly assumed a deterministic signature. DSA is however supposed to take random value k for signing. However that randomness is ...
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Is piping a `ssh-agent` signed message as a password secure?

There's an encrypted filesystem on a server I ssh into using public key authentication. Since a forwarded ssh-agent can deterministically sign a message (see also the ssh-agent protocol section ...
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How does ssh public key authentication work?

My basic understanding is this: The (connected to) server's sshd uses the public key to encrypt some message The client's ssh or ssh-agent decrypts it and sends something back (the message's ...
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Is it okay to widely share the RSA key fingerprint for a host?

When you ssh into a remote box for the first time or if the remote host's key fingerprint has changed (from what's stored in your known_hosts file) you get a warning and you are shown the fingerprint ...
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1answer
624 views

Why does the OpenSSH client on Mac OS X silently launch an ssh-agent for the user?

I'm confused by the difference in behavior of ssh clients I'm seeing on two different hosts. Just to be clear, this is the scenario: "macbox" OS X using OpenSSH_5.2p1 ssh client "sunbox" Solaris 10 ...
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2answers
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Security Concerns with TCP Forwarding

Until now I've been setting TCP Forwarding in ssh always blindly to no but searching on the net, I have trouble finding out what the actual security threat is, when allowing it. The one thing I did ...
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3answers
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Can the root of a system access to unencrypted data when using a double tunnel?

I connect to a DMZ gateway system (B) which is not secured. From this machine (B) I can connect to the final destination (C). A-->B-->C I created a ssh tunnel from A to B and forwarding the port 22 ...
4
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1answer
802 views

Are SSH packets encrypted even before new keys are sent?

What format does SSH use to exchange (encrypted / plain) packets before new keys are derived? SSH Document says that after key exchange, client and server use negotiated algorithm to encrypt the ...
3
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1answer
283 views

What dangers are there in storing my private key on different servers?

This question is specifically concerned with storing keys in the cloud, and is somewhat applicable. But I've got a laptop and a desktop computer at home - I'm the admin on both of those systems, and ...
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Invalid users trying to log in to my server

I'm seeing a lot of log entries that appear to be failed login attempts from unknown IP addresses. I am using private and public keys to log in with SSH but I have noticed that even with private ...
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What is the difference between authorized_key and known_host file for SSH?

I am learning basics of SSH protocol. I am confused between the contents of the following 2 files: ~/.ssh/authorized_keys: Holds a list of authorized public keys for servers. When the client ...
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How to create ssh tunnel using netcat?

I want to create reverse connection between two machines, but these is a firewall in the middle preventing all connections, except ssh. I want to create ssh tunnel using netcat, could you please tell ...
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0answers
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Hack scenario when a person has a non-superuser shell [closed]

Suppose that there are following three machines in the network: Machine A: Microsoft Server 2003 Service Pack 2 FileZilla 0.9.29 beta ftp server (TCP 21) Mcafee ePolicy server (81), remote desktop ...
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sniff SSH password on the server

Is it possible on the server to log the password encoded by the remote user inside a log. I want to make a honeypot to see the type of user/password used.
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Confusion: Why isn't a passhrase encrypted SSH key two factor auth?

I'm trying to figure out the best practices for accessing my devbox from a public terminal. Most sources I've found recommend protecting the box with some kind of two factor authentication, such as ...
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How do RSA fingerprints protect from MITM attacks?

I understand that RSA fingerprints are used to verify that you are really connecting directly to who you want to connect to, and not someone else posing as that site. Like when you do a git push, it ...
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4answers
761 views

Can public keys be a security risk when performing password-less SSH logins?

Some companies use monitoring software such as nagios or icinga. In order to perform checks on the servers, they often need password-less SSH logins. The servers being checked put the public key of ...
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Creating user specific authentication methods in SSH

I have configured sshd on an Ubuntu server to use key authentication and it is working fine. I had to disable password authentication for key authentication to work. Server is always accessed via ...
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Possible to use both private key and password authentication for ssh login?

It seems that they are mutually exclusive, as disabling one gives me the other, and vice versa. Two-factor auth for my ssh servers sounds really nice, so is there any way to accomplish this?
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Do these mysql and ssh issues mean my rails server was hacked?

I'm running a rails application on an ubuntu server on slicehost. I got a pingdom alert that the server was unreachable, so I tried to load the website in my browser. It showed a Passenger error, ...
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3answers
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What are potential security risks when using an insecure wireless connection?

If someone is using an insecure wireless connection (for example a hot spot in a coffee shop) does it posse a threat even if the person is using a secure application layer protocol? What I mean by ...
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3answers
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In the Diffie-Hellman key exchange, how is the shared base key 'p' known and how are A and B, protected from Eve?

I'm trying to wrap my head around Hellman, Diffie, and Merkle's key exchange design, but after reading the Wiki article about it, I can't figure out how the commonly known factor ('p', I think) comes ...
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0answers
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How often should an SSH key pair be changed? [duplicate]

Possible Duplicate: How often should an SSH key pair be changed? I've been using a passphrase-protected 1024-bit RSA key for passwordless SSH via ssh-agent between my own systems for years. ...
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How often should an SSH key pair be changed?

I've been using a 1024-bit RSA key for passwordless SSH between my own systems for years. More recently I've also started using it for passwordless access to my hosting providers and to source code ...
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SSH : Remote Host Identification Changed

As part of my daily routine, I was SSH'ing to one of the corporate servers. However this time I was presented with following message @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ @ ...
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Security Concerns with X11 Forwarding

What are some of the security concerns and reasons either for or against allowing X11 Forwarding. I have generally taken an approach of not allowing it under the blanket guise of security. Recently, ...
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Is there an easy way to see a log of SCP activity on a server (ala /var/log/secure for ssh login)?

On Linux systems, /var/log/secure (or similar, depending on distro) shows all SSH login activity. Is there a similar log for SCP? If not, what's a good approach to enabling logging of scp activity ...