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I am wanting to setup passwordless authentication to my remote linux server, I was going to generate an RSA public/private keypair. I was thinking about cipher strength like 2048 bit and 4096 bit. This got me to wondering, does the size of my cipher have any impact on my actual internet connection? Or the cipher bog the computer down only because this is where the decrypt and encrypt is taking place? Because when it comes to me exposing server to the public internet I tend to get paranoid that someone may take over the server or something. But I cannot use a VPN because my school block the port(s) use for VPN.

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up vote 7 down vote accepted

Two things to keep in mind:

  1. The private key gets sent to the server to verify if it matches the public key.

    This computation has to be done by the server, not the client.

  2. Authentication is only performed when establishing a connection, not afterwards. The actual data encryption always uses symmetric ciphers, since they are much, much faster.

    4096 bit is much more secure than 2048 bit (although the latter should be sufficient), but there will be no tangible speed difference.

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ssh key is only used for the authentication, not for encrypting the actual ssh traffic, and the key size effect on the traffic is very minimal. the subsequent traffic is encrypted by key exchanges between the client and server and is not affected by your public/private key exchange.

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