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| 2007-06-06 | 2007-06-15 | ||
| no summary (67.163.93.71) | no summary (Ted Engel) | ||
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| ====== Understanding SSH ====== | ====== Understanding SSH ====== | ||
| - | SSH is a cryptographically protected remote login protocol that replaces insecure telnet and rlogin protocols. SSH provides strong protection against password sniffing and third party session monitoring, better protecting your authentication credentials | + | SSH is a cryptographically protected remote login protocol that replaces insecure telnet and rlogin protocols. It provides strong protection against password sniffing and third party session monitoring, better protecting your authentication credentials |
| - | and privacy. In addition to protecting your passwords and your privacy, | + | and privacy. In addition,·SSH offers additional authentication methods that are considered more·secure than passwords, such as public key authentication and extensive |
| - | SSH offers additional authentication methods that are considered more | + | |
| - | secure than passwords, such as public key authentication, and extensive | + | |
| protection against spoofing. | protection against spoofing. | ||
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| Generally, the client will choose methods that are the least intrusive | Generally, the client will choose methods that are the least intrusive | ||
| to the user, if they are available. In most cases, the client provides | to the user, if they are available. In most cases, the client provides | ||
| - | the option to choose which methods can be used. In WinSCP you can configure this on [[ui_login_authentication|Login dialog]]. | + | the option to choose which methods can be used. In WinSCP, you can configure this on [[ui_login_authentication|Login dialog]]. |
| The actual order of authentication methods is as follows: MIT Kerberos GSSAPI 5 (SSH-2 only), [[public key]] (using Pageant), [[public key]] (using [[ui_login_session|configured file]]), keyboard-interactive (SSH-2 only), TIS or Cryptocard (SSH-1 only), password. | The actual order of authentication methods is as follows: MIT Kerberos GSSAPI 5 (SSH-2 only), [[public key]] (using Pageant), [[public key]] (using [[ui_login_session|configured file]]), keyboard-interactive (SSH-2 only), TIS or Cryptocard (SSH-1 only), password. | ||
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| This is a feature of the SSH protocol. It is designed to protect you against a network attack known as spoofing: secretly redirecting your connection to a different computer, so that you send your password to the wrong machine. Using this technique, an attacker would be able to learn the password that guards your login account, and could then log in as if they were you and use the account for their own purposes. | This is a feature of the SSH protocol. It is designed to protect you against a network attack known as spoofing: secretly redirecting your connection to a different computer, so that you send your password to the wrong machine. Using this technique, an attacker would be able to learn the password that guards your login account, and could then log in as if they were you and use the account for their own purposes. | ||
| - | To prevent this attack, each server has a unique identifying code, called a host key. These keys are created in a way that prevents one server from forging another server's key. So if you connect to a server and it sends you a different host key from the one you were expecting, WinSCP can warn you that the server may have been switched and that a spoofing attack might be in progress. | + | To prevent this attack, each server has a unique identifying code, called a host key. These keys prevent a server from forging another server's key. If you connect to a server and you receive an unexpected host key, WinSCP can warn you that the server may have been switched and that a spoofing attack might be underway. |
| - | WinSCP records the host key for each server you connect to, in the [[config|configuration storage]]. Every time you connect to a server, it checks that the host key presented by the server is the same host key as it was the last time you connected. If it is not, you will see a warning, and you will have the chance to abandon your connection before you type any private information (such as a password) into it. | + | WinSCP records the host key for each server you connect to, in the [[config|configuration storage]]. Every time you connect to a server, it compares the server's host key to the host key you received the last time you connected. If the keys differ, you will receive a warning and a chance to abandon your connection before you enter any private information such as a password. |
| - | However, when you connect to a server you have not connected to before, WinSCP has no way of telling whether the host key is the right one or not. So it gives the warning shown above, and asks you whether you want to trust this host key or not. | + | However, when you connect to a server for the first time, WinSCP has no way of telling whether the host key is the right one or not. So it gives the warning shown above, and asks you whether you want to trust this host key or not. |
| Whether or not to trust the host key is your choice. If you are connecting within a company network, you might feel that all the network users are on the same side and spoofing attacks are unlikely, so you might choose to trust the key without checking it. If you are connecting across a hostile network (such as the Internet), you should check with your system administrator, perhaps by telephone or in person. (Some modern servers have more than one host key. If the system administrator sends you more than one fingerprint, you should make sure the one WinSCP shows you is on the list, but it doesn't matter which one it is.) ((&puttydoccite)) | Whether or not to trust the host key is your choice. If you are connecting within a company network, you might feel that all the network users are on the same side and spoofing attacks are unlikely, so you might choose to trust the key without checking it. If you are connecting across a hostile network (such as the Internet), you should check with your system administrator, perhaps by telephone or in person. (Some modern servers have more than one host key. If the system administrator sends you more than one fingerprint, you should make sure the one WinSCP shows you is on the list, but it doesn't matter which one it is.) ((&puttydoccite)) | ||
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| ===== Compression ===== | ===== Compression ===== | ||
| - | SSH supports compression of the data stream between the client | + | SSH supports data stream compression between the client |
| - | and the server. On slow links, this may increase throughput, however, | + | and the server. On slow links, this may increase throughput, while in faster connections the added CPU overhead may actually result in |
| - | with faster connections the added CPU overhead may actually result in | + | slower transfers, particularly depending on the data type you're transferring. Large text files may still benefit significantly, while |
| - | slower transfers, particularly depending on the type of data being | + | binaries may transfer more slowly. You may want to |
| - | transferred - large text files may still benefit significantly, while | + | |
| - | binaries may actually transfer more slowly. You may want to | + | |
| experiment to find what works best in your situation. Compression may | experiment to find what works best in your situation. Compression may | ||
| - | also improve security slightly, in part by rendering known-cyphertext | + | also improve security slightly, in part by rendering known·cyphertext |
| - | attacks more difficult to execute and by providing less data for | + | attacks more difficult and by providing less data for |
| cryptanalysis. | cryptanalysis. | ||