Colt 1, 6 6 gold badges 20 20 silver badges 25 25 bronze badges. He says he's on Ubuntu, and as theotherreceive says, Ubuntu hashes by default. 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. Stack Gives Back Safety in numbers: crowdsourcing data on nefarious IP addresses. Featured on Meta. New post summary designs on greatest hits now, everywhere else eventually.
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If it is not hashed you can use: unix. Add a comment. Active Oldest Votes. If you know the hostname you're looking for ahead of time, you can search for it with: ssh-keygen -H -F hostname Or, if SSH runs on port other than Use literal brackets [].
Improve this answer. Toby Speight 7, 1 1 gold badge 19 19 silver badges 45 45 bronze badges. Does hash known hosts essentially mean it's not possible? Then when you attempt to connect to SSH with username 'bob' and your private key it will ask the OS "I got this guy name 'bob', can be be here? If both answers are yes, then you are allowed in.
Whenever SSH is configured on a new server it always generates a public and private key for the server, just like you did for your user. Every time you connect to an SSH server, it shows you its public key, together with a proof that it possesses the corresponding private key.
If you have the key, and it matches, then you connect straight away. If the keys do not match, then you get a big nasty warning. This is where things get interesting. The 3 situations that a key mismatch typically happens are:. This is an over-simplification; there are lots more capabilities and complications to "ssh" than are mentioned here.
While it has been said that public-key values "can be safely strewn about like seeds in the wind," keep in mind that it's the gardner, not the seed-pod, who decides which seeds get established in the garden.
Altough a public-key is not secret, fierce protection is required to preserve the trusted association of the key with the thing that the key is authenticating. For a public-key to be relevant to "ssh," the key must be registered ahead of time, and stored in the appropriate secure file. This general truth has one important exception, which will be discussed later. The server and client each have their own, securely stored list of public-keys; a login will succeed only if each side is registered with the other.
These files are similar in that each has text with one public-key per line, but they have subtle differences in format and usage. A public-private key pair are used to perform "asymmetric cryptography.
The challenge is created by encoding with one key, and answered by decoding with the other key. In "ssh", both sides client and server are suspicious of the other; this is an improvement over the predecessor to "ssh," which was "telnet".
With "telnet", the client was required to provide a password, but the server was not vetted. The lack of vetting allowed "man-in-the-middle" attacks to occur, with catastrophic consequences to security.
By contrast, in the "ssh" process, the client surrenders no information until the server first answers a challenge. Before sharing any login information, the "ssh" client first eliminates the opportunity for a man-in-the-middle attack by challenging the server to prove "Are you really who I think you are? Once the server has authenticated, it gets a chance to challenge the client. When none of those keys works, the "sshd" process falls-back on password style authentication.
So for "ssh", as with any login process, there are lists of "friends", and only those on the list are allowed to attempt to pass a challenge. The server doesn't care where the login is coming from, but only where it's going. The client is attempting to access a particular account, the account name was specified as a parameter when "ssh" was invoked. Although there are many capabilities that can be expressed in a configuration entry, the basic, most common usage has the following parameters.
Note that parameters are separated by space characters. Note that the token ssh-rsa indicates that the algorithm used for encoding is "rsa". Other valid algorithms include "dsa" and "ecdsa". Therefore, a different token might take the place of the ssh-rsa shown here. In both cases, if the public key is not found within a secure file, then assymetric encryption does not happen. As mentioned earlier, there is one exception to this rule.
The "ssh" program warns the user, but if the user chooses to go forward, the "ssh" client allows it "just this once. This exception totally subverts security by allowing the adversary to provide the association of a server-name with a public-key. Asked 10 years, 6 months ago. Active 2 years, 8 months ago. Viewed k times.
Improve this question. Don't remove it. Update the line to change the IP address from the old one to the new one to avoid opening a window for an attacker to impersonate the host. Add a comment. Active Oldest Votes.
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