Originally the difference was for version differentiation. But don't bother any more, as now the 2 can be ignored. IQAndreas 1, 2 2 gold badges 15 15 silver badges 37 37 bronze badges. It becomes especially important when shared homes are used as they generally are on a cluster. It is a real shame it is now depreciated. I did not know you can list multiple files in that option. Especially as the first words in the manpage for it was Specifies the file that Singular file rather than plural files.
But that was clarified later. Thanks again. The Overflow Blog. Does ES6 make JavaScript frameworks obsolete? Podcast Do polyglots have an edge when it comes to mastering programming Featured on Meta. Now live: A fully responsive profile. Forces a command to be executed when this key is used for authentication.
This is also called command restriction or forced command. The effect is to limit the privileges given to the key, and specifying this options is often important for implementing the principle of least privilege. Without this option, the key grants unlimited access as that user, including obtaining shell access.
It is a common error when configuring SFTP file transfers to accidentally omit this option and permit shell access. Specifies an environment variable and its value to be added to the environment before executing shell or command. Specifies a source restriction or from-stanza , restricting the set of IP addresses or host names from which the reverse-mapped DNS names from which the key can be used. More than one pattern may be specified by separating them by commas. An exclamation mark!
Prevents port forwarding for connections using this key. This can be important for, e. Forgetting to disable port forwarding can allow SSH tunneling to be performed using keys only intended for file transfers. Prevents allocation of a pseudo-tty for connections using the key. 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. This security risk is allowed because it makes things so much easier for so many people. But for low-risk situations, the extra work might be pointless. The friend might use the same public-private key pair to access multiple, different servers.
This allows a single key-pair to authenticate to all servers ever contacted. Sometimes, users who work from multiple client machines will replicate the same key pair; typically this is done when a user works on a desk-top and a lap-top. For the server side, a system process, or daemon, handles all incoming "ssh" login requests.
The daemon is named "sshd". For the client side, you invoke "ssh" or "scp" when you need it. Your command line will include various parameters, one of which may optionally specify which private key to use. It is not the public or private key of the remote host. If you SFTP to an address that might resolve to several varying hosts load balanced etc you must add the fingerprints from all the possible end points, or it will work initially and then fail when it is routed to the second or subsequent host.
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Active 2 years, 2 months ago. Viewed k times. I am not sure what this means.
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