Differences
This shows you the differences between the selected revisions of the page.
| ssh_keys 2018-07-06 | ssh_keys 2024-07-17 (current) | ||
| Line 1: | Line 1: | ||
| ====== 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 ===== | ===== User Private Key ===== | ||
| - | A //user private key// is key that is 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/hers identity. | + | 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. |
| 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. | 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. | ||
| - | Different file formats are used to store private keys. WinSCP supports PuTTY format, with ''.ppk'' extension. | + | Different file formats are used to store private keys. WinSCP supports PuTTY format, with the ''.ppk'' extension. |
| - | + | ||
| - | //Note that there's always a user key-pair involved, even when a password authentication method is used, when no key-pair seemingly exists. In this case an ad-hoc generated key-pair is used. Such key-pair is used for encryption only. It cannot be used for authentication, as the server does not recognize the matching public key. The password is used for authentication.// | + | |
| ===== User Public Key ===== | ===== 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. | 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. | ||
| - | To allow authorization of the user on a server, the user public key is registered on the server. In the most widespread SSH server implementation, the OpenSSH, file ''~/.ssh/authorized_keys'' is used for that. | + | 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. |
| //Learn more about [[public_key|public key authentication]] in general and how to [[guide_public_key|setup authentication with public keys]].// | //Learn more about [[public_key|public key authentication]] in general and how to [[guide_public_key|setup authentication with public keys]].// | ||
| ===== Host Private Key ===== | ===== 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. | + | 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. |
| ===== Host Public Key ===== | ===== 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 host identity. | + | 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. |
| - | 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. | + | 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. |