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How SSH Public Key Authentication Works (Choosing the Right Keys)

As far as I know about SSH authentication and, according to many explanations with Alice and Bob, there are several important steps:

  • The client creates a pair of public / private keys and publishes the public key on the server.
  • When the server receives a public key authentication request, it generates random data, encrypts it using the client’s public key, and sends it to the client.
  • The client decrypts this data using the private key and sends it as an authentication.

I hope that some of you will help me understand how then the GitHub server knows which public key to choose in step 2 when I clone an arbitrary repository using SSH? It has millions of public user keys to choose from. And the user could install several private keys on his computer.

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The bit protocol is more active than you think. The manpage describes that the client tells the server which key he wants to use:

~/.ssh/authorized_keys , .       , ssh ,      . , ,       .

SSH rfc , SSH_MSG_USERAUTH_REQUEST.

github . , , .

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Source: https://habr.com/ru/post/1540023/

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