Update ssh-key-management.md

docs.it4i/general/accessing-the-clusters/shell-access-and-data-transfer/ssh-key-management.md

-# SSH Key Management
+# SSH
+
+Secure Shell (SSH) is a cryptographic network protocol for operating network services securely over an unsecured network.
+SSH uses public-private key pair for authentication, allowing users to log in without having to specify a password. The public key is placed on all computers that must allow access to the owner of the matching private key (the private key must be kept **secret**).
+
+## Private Key
+
+!!! note
+    The path to a private key is usually /home/username/.ssh/
+
+A private key file in the `id_rsa` or `*.ppk` format is present locally on local side and used for example in the Pageant SSH agent (for Windows users). The private key should always be kept in a safe place.
+
+An example of private key format:
+
+```console
+    -----BEGIN RSA PRIVATE KEY-----
+    MIIEpAIBAAKCAQEAqbo7jokygnBpG2wYa5NB45ns6+UKTNLMLHF0BO3zmRtKEElE
+    aGqXfbYwvXlcuRb2d9/Y5dVpCZHV0kbY3NhtVOcEIe+1ROaiU9BEsUAhMNEvgiLV
+    gSql4QvRO4BWPlM8+WAWXDp3oeoBh8glXyuh9teb8yq98fv1r1peYGRrW3/s4V+q
+    O1SQ0XY2T7rWCYRLIP6rTMXArTI35v3WU513mn7nm1fJ7oN0QgVH5b0W9V1Kyc4l
+    9vILHeMXxvz+i/5jTEfLOJpiRGYZYcaYrE4dIiHPl3IlbV7hlkK23Xb1US8QJr5G
+    ADxp1VTkHjY+mKagEfxl1hQIb42JLHhKMEGqNQIDAQABAoIBAQCkypPuxZjL+vai
+    UGa5dAWiRZ46P2yrwHPKpvEdpCdDPbLAc1K/CtdBkHZsUPxNHVV6eFWweW99giIY
+    Av+mFWC58X8asBHQ7xkmxW0cqAZRzpkRAl9IBS9/fKjO28Fgy/p+suOi8oWbKIgJ
+    3LMkX0nnT9oz1AkOfTNC6Tv+3SE7eTj1RPcMjur4W1Cd1N3EljLszdVk4tLxlXBS
+    yl9NzVnJJbJR4t01l45VfFECgYEAno1WJSB/SwdZvS9GkfhvmZd3r4vyV9Bmo3dn
+    XZAh8HRW13imOnpklDR4FRe98D9A7V3yh9h60Co4oAUd6N+Oc68/qnv/8O9efA+M
+    /neI9ANYFo8F0+yFCp4Duj7zPV3aWlN/pd8TNzLqecqh10uZNMy8rAjCxybeZjWd
+    DyhgywXhAoGBAN3BCazNefYpLbpBQzwes+f2oStvwOYKDqySWsYVXeVgUI+OWTVZ
+    eZ26Y86E8MQO+q0TIxpwou+TEaUgOSqCX40Q37rGSl9K+rjnboJBYNCmwVp9bfyj
+    kCLL/3g57nTSqhgHNa1xwemePvgNdn6FZteA8sXiCg5ZzaISqWAffek5AoGBAMPw
+    V/vwQ96C8E3l1cH5cUbmBCCcfXM2GLv74bb1V3SvCiAKgOrZ8gEgUiQ0+TfcbAbe
+    7MM20vRNQjaLTBpai/BTbmqM1Q+r1KNjq8k5bfTdAoGANgzlNM9omM10rd9WagL5
+    yuJcal/03p048mtB4OI4Xr5ZJISHze8fK4jQ5veUT9Vu2Fy/w6QMsuRf+qWeCXR5
+    RPC2H0JzkS+2uZp8BOHk1iDPqbxWXJE9I57CxBV9C/tfzo2IhtOOcuJ4LY+sw+y/
+    ocKpJbdLTWrTLdqLHwicdn8OxeWot1mOukyK2l0UeDkY6H5pYPtHTpAZvRBd7ETL
+    Zs2RP3KFFvho6aIDGrY0wee740/jWotx7fbxxKwPyDRsbH3+1Wx/eX2RND4OGdkH
+    gejJEzpk/7y/P/hCad7bSDdHZwO+Z03HIRC0E8yQz+JYatrqckaRCtd7cXryTmTR
+    FbvLJmECgYBDpfno2CzcFJCTdNBZFi34oJRiDb+HdESXepk58PcNcgK3R8PXf+au
+    OqDBtZIuFv9U1WAg0gzGwt/0Y9u2c8m0nXziUS6AePxy5sBHs7g9C9WeZRz/nCWK
+    +cHIm7XOwBEzDKz5f9eBqRGipm0skDZNKl8X/5QMTT5K3Eci2n+lTw==
+    -----END RSA PRIVATE KEY-----
+```
+
+## Public Key
+
+A public key file in the `*.pub` format is present on the remote side and allows an access to the owner of the matching private key.
+
+An example of public key format:
+
+```console
+ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQCpujuOiTKCcGkbbBhrk0Hjmezr5QpM0swscXQE7fOZG0oQSURoapd9tjC9eVy5FvZ339jl1WkJkdXSRtjc2G1U5wQh77VE5qJT0ESxQCEw0S+CItWBKqXhC9E7gFY+UyP5YBZcOneh6gGHyCVfK6H215vzKr3x+/WvWl5gZGtbf+zhX6o4RJDRdjZPutYJhEsg/qtMxcCtMjfm/dZTnXeafuebV8nug3RCBUflvRb1XUrJuiX28gsd4xfG/P6L/mNMR8s4kmJEZhlhxpj8Th0iIc+XciVtXuGWQrbddcVRLxAmvkYAPGnVVOQeNj69pqAR/GXaFAhvjYkseEowQao1 username@organization.example.com
+```
+
+## SSH Key Management
 
 When you first create an account with IT4Innovations, you receive an SSH key with your credentials. However, you can manage your own SSH key for authentication to clusters.