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Also I'm not sure how to run this non interactive in a script. Supported Ciphers, MACs and KexAlgorithms are always available in manual and this doesn't have anything in common with key lengths. It fits in one line:. Sign up to join this community. The best answers are voted up and rise to the top. Home Questions Tags Users Unanswered. Ask Question. Asked 4 years, 5 months ago.
Active 1 year, 10 months ago. Viewed 47k times. Is there a convenient way to get SSH connection information?
Improving ssh/scp Performance by Choosing Suitable Ciphers
Henrik Pingel. Henrik Pingel Henrik Pingel 5, 2 2 gold badges 17 17 silver badges 35 35 bronze badges. However, it seems that those outputs are limited to what both sides support, making them less useful for a security audit. Active Oldest Votes. You miss few points in your question: What is your openssh version? It can differ a bit over the versions. ServerKeyBits is option for protocol version 1, which you have hopefully disabled! Jakuje Jakuje 7, 2 2 gold badges 28 28 silver badges 36 36 bronze badges.
RHEL6 host with latest openssh update should have it fixed as well. I only checked on an outdated VM Jan 9 '19 at It fits in one line: nmap --script ssh2-enum-algos -sV -p 22 1.
Nmap done: 1 IP address 1 host up scanned in 0. Did you literally use the command, or did you replace 1. I used the IP of my server. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. The Overflow Blog.Update on Oct. Instead, you may consider ChaCha20 as suggested by Tony Arcieri.
If you are building something new, there is absolutely zero reason to choose it. The answer is of course yes. The ciphers used have a large impact on the performance. Note that SSH 2 supported ciphers have more variance :. Specifies the ciphers allowed for protocol version 2 in order of preference.
Multiple ciphers must be comma-separated. The supported ciphers are 3des-cbc aescbc aescbc aescbc aesctr aesctr aesctr aesgcm openssh. The default is:. Although arcfour is the fastest, there are concerns about its security. Hence, my default choice is blowfish for both speed and security. According to the OpenSSH ssh man page :. The supported values are 3des blowfish and des. It is believed to be secure. It is also a good idea to enable compression by default so that ssh performs better over a low-bandwidth link, such as a slow Internet connection.
The 3rd and 4th lines enable compression and set its level. Eric is a systems guy. Eric is interested in building high-performance and scalable distributed systems and related technologies. The views or opinions expressed here are solely Eric's own and do not necessarily represent those of any third parties. Below is a script I made that you can use to benchmark each cipher. The results should report realistic maximum transfer throughput.
Information Security Stack Exchange is a question and answer site for information security professionals. It only takes a minute to sign up. 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.
I am assuming you are talking about the symmetric ciphers used. If you are also wondering about the HMAC and key exchange, I can edit my answer to explain which of those are strong or weak as well. AES and ChaCha20 are the best ciphers currently supported. ChaCha20 is a more modern cipher and is designed with a very high security margin.
It is very fast. ChaCha20 on the other hand is a stream cipher, so it does not use a block mode of operation and is therefore not able to use CBC insecurely. As long as the underlying cipher is secure, the authentication will be unbroken. This means the key must be reseeded periodically. This is not horrible, but it is not ideal. The issue with bit block sizes is described quite well on the Sweet32 websitedescribing the attacks made possible. The gist of it is that encrypting a large amount of data with a single key can leak information about the plaintext.
When 32 GiB of data are encrypted, things get really bad. It's often recommended to change keys after every 4 GiB. While small block sizes are not great, OpenSSH does automatically reseed these ciphers more often than otherwise to attempt to mitigate this flaw. The ciphers themselves are not particularly bad.
Super User is a question and answer site for computer enthusiasts and power users. It only takes a minute to sign up. And there is an online service called sshcheck.How SSH key Works ?
Some old versions of OpenSSH do not support the -Q option, but this works for any ssh and it has the benefit of showing both client and server options, without the need for any third party tools like nmap :.
Sign up to join this community. The best answers are voted up and rise to the top. Home Questions Tags Users Unanswered. Ask Question. Asked 5 years, 2 months ago. Active 1 month ago. Viewed 73k times. I'd like to find out dynamically instead of having to look at the source. Colin Dean Colin Dean 1, 3 3 gold badges 11 11 silver badges 9 9 bronze badges. Active Oldest Votes. I knew it seemed crazy that I couldn't find it. Specifically, -Q was introduced in version 6.
How to differentiate supported from enabled as default? This is in reference of OpenSSH 8. Host is up 0. Please report any incorrect resu Service detection performed. Please report any incorrect resu Nmap done: 1 IP address 1 host up scanned in 0.
Some old versions of OpenSSH do not support the -Q option, but this works for any ssh and it has the benefit of showing both client and server options, without the need for any third party tools like nmap : ssh -vv username servername Scan the output to see what ciphers, KEX algos, and MACs are supported Michael - Where's Clay Shirky 7 7 silver badges 14 14 bronze badges.
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This page is about configuring the OpenSSH server. For configuring public key authentication, see ssh-keygen. The OpenSSH server reads a configuration file when it is started. Some organizations run multiple SSH servers at different port numbers, specifying a different configuration file for each server using this option.
The default values for certain configuration options in OpenSSH are quite restrictive and often need to be changed. Usually this is done by editing the default configuration file to change just a few options. The SSH server actually reads several configuration files. It may also refer to a number of other files.
Cipher Security: How to harden TLS and SSH
Many individual developers and power users wish to maximize their convenience rather than go for maximum security. For such use, we recommend the following settings for homes, development servers, and universities. For important systems even such organizations should follow the guidelines for configuring enterprise servers. Larger enterprises, or others wanting to run a tight security policy for certain servers, may want to configure the following configuration options.
Symmetric algorithms for encrypting the bulk of transferred data are configured using the Ciphers option. A good value is aesctr,aesctr,aesctr. This should also provide good interoperability. Host key algorithms are selected by the HostKeyAlgorithms option. Key exchange algorithms are selected by the KexAlgorithms option. We recommend ecdh-sha2-nistp,ecdh-sha2-nistp,ecdh-sha2-nistp,diffie-hellman-groupsha1,diffie-hellman-group-exchange-sha In particular, we do not recommend allowing diffie-hellman-group1-sha1unless needed for compatibility.
It uses a bit prime number, which is too small by today's standards and may be breakable by intelligence agencies in real time. Using it could expose connections to man-in-the-middle attacks when faced with such adversaries. Message authentication code algorithms are configured using the MACs option.
A good value is hmac-sha,hmac-sha,hmac-sha1. We have included the sha-1 algorithm in the above sets only for compatibility.It can be used as a test tool to determine the appropriate cipherlist. If it is not included then the default cipher list will be used.
The format is described below. The cipher list consists of one or more cipher strings separated by colons. Commas or spaces are also acceptable separators but colons are normally used. It can represent a list of cipher suites containing a certain algorithm or cipher suites of a certain type.
This is used as a logical and operation. Each cipher string can be optionally preceded by the characters! The ciphers deleted can never reappear in the list even if they are explicitly stated. If - is used then the ciphers are deleted from the list, but some or all of the ciphers can be added again by later options. This option doesn't add any new ciphers it just moves matching existing ones. If none of these characters is present then the string is just interpreted as a list of ciphers to be appended to the current preference list.
If the list includes any ciphers already present they will be ignored: that is they will not moved to the end of the list. This is determined at compile time and is normally ALL:! This must be the first cipher string specified. This currently means those with key lengths larger than bits.
Because these offer no encryption at all and are a security risk they are disabled unless explicitly included. This is currently the anonymous DH algorithms. These cipher suites are vulnerable to a "man in the middle" attack and so their use is normally discouraged.
Not implemented. Some compiled versions of OpenSSL may not include all the ciphers listed here because some ciphers were excluded at compile time. TLS v1. Additional Export and other cipher suites SSL v2. The actual cipher string can take several different forms. Including 40 and 56 bits algorithms. SSL v3.I am using RHEL 7. Could anyone please point me to the correct names to disable?
So I stop then run systemctl grep sshd. To test the cypers, type ssh -vv localhost Look for the listing of allowed ciphers. This solution doesn't cite rhel7. Also, ciphers are evaluated in order, so the correct line ought to be: 'Ciphers aesctr,aesctr,aesctr'. In RHEL6. I have change this MACs hmac-sha1,hmac-sha,hmac-sha but sshd service is not working in rhel 5. Blunt advice : RHEL 5. Christian is absolutely correct.
RHEL 5. Was there another change? Can you revert your change and attempt ssh? Please highly consider replacing that server, however while you have it, either consider temporarily reverting your recent changes that caused the issue, or try a different MACs configuration in that file.
See next Red Hat Solution below. Please take Christian Labisch's advice above, build a new system with a supported version of Red Hat. Comments Thank you in advanced. Newbie 10 points. Log in to join the conversation. JH Newbie 10 points. Jason Hotchkiss. Answered my own issue, I believe, any willing to confirm? Guru points. Hinton Community Leader.