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| ssh_keys 2019-02-28 | ssh_keys 2024-07-17 (current) | ||
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| ====== Understanding SSH Key Pairs ====== | ====== Understanding SSH Key Pairs ====== | ||
| - | In every SSH/SFTP connection there are four keys (or two key-pairs) involved. This article explains a difference between them and what keys an %%SFTP%% client user needs to care about. | + | In every SSH/SFTP connection, there are four keys (or two key·pairs) involved. This article explains the difference between them and what keys an %%SFTP%% client user needs to care about. |
| - | The %%SSH%% employs a public key cryptography. A [[wp>Public-key_cryptography|public-key cryptography]], also known as asymmetric cryptography, is a class of cryptographic algorithms which requires two separate keys, one of which is secret (or private) and one of which is public.((&wikipedia_ref(Public-key_cryptography|Public-key cryptography))) Together they are known as a key-pair. In %%SSH%%, the public key cryptography is used in both directions (client to server and server to client), so two key pairs are used. One key pair is known as a host (server) key, the other as a user (client) key. | + | The %%SSH%% employs public key cryptography. A [[wp>Public-key_cryptography|public-key cryptography]], also known as asymmetric cryptography, is a class of cryptographic algorithms which requires two separate keys, one of which is secret (or private) and one of which is public.((&wikipedia_ref(Public-key_cryptography|Public-key cryptography))) Together they are known as a key·pair. In %%SSH%%, the public key cryptography is used in both directions (client to server and server to client), so two key pairs are used. One key pair is known as a host (server) key, and the other is a user (client) key. |
| + | ===== User Private Key ===== | ||
| + | A //user private key// is a key kept secret by the %%SSH%% user on his/her client machine. The user must never reveal the private key to anyone, including the server (server administrator), not to compromise his/her identity. | ||
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| + | To protect the private key, it should be generated locally on a user's machine (e.g. using [[ui_puttygen|PuTTYgen]]) and stored encrypted by a passphrase. The passphrase should be long enough (that's why it's called passphrase, not password) to withstand a [[wp>Brute-force_attack|brute-force attack]] for a reasonably long time, in case an attacker obtains the private key file. | ||
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| + | Different file formats are used to store private keys. WinSCP supports PuTTY format, with the ''.ppk'' extension. | ||
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| + | ===== User Public Key ===== | ||
| + | A user public key is a counterpart to //user private key//. They are generated at the same time. The //user public key// can be safely revealed to anyone, without compromising user identity. | ||
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| + | To allow user authorization on a server, the user's public key is registered on the server. In the most widespread %%SSH%% server implementation, the OpenSSH, file ''~/.ssh/authorized_keys'' is used for that. | ||
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| + | //Learn more about [[public_key|public key authentication]] in general and how to [[guide_public_key|setup authentication with public keys]].// | ||
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| + | ===== Host Private Key ===== | ||
| + | A //host private key// is generated when the %%SSH%% server is set up. It is safely stored in a location that should be accessible by a server administrator only. The user connecting to the %%SSH%% server does not need to care about //host private key// in general. | ||
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| + | ===== Host Public Key ===== | ||
| + | A //host public key// is a counterpart to //host private key//. They are generated at the same time. The //host public key// can be safely revealed to anyone, without compromising the host's identity. | ||
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| + | To allow authorizing the host to the user, the user should be [[faq_hostkey|provided with host public key in advance]], before connecting. The client application typically prompts the user with //host public key// on the first connection to allow the user to [[ssh_verifying_the_host_key|verify/authorize the key]]. The //host public key// is then saved and verified automatically on further connections. The client application warns the user if the host key changes. | ||