How to resolve Java UnknownHostKey, while using JSch SFTP library?

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You are trying to skip a host key checking by setting StrictHostKeyChecking to no.

But you have to do that before the checking, i.e. before the session.connect().

Anyway, you should never do this, unless you do not care about security. The host key checking is there to protect you from man-in-the-middle attacks.

Instead, set up an expected host key to let JSch verify it.

For example:

  • Call JSch.setKnownHosts providing a path to a .ssh/known_hosts-like file.

    To generate the .ssh/known_hosts-like file, you can use an ssh-keyscan command from OpenSSH. If you are connecting from a *nix server, you should have the command available, just run

    ssh-keyscan example.com > known_hosts

    It will have a format like:

    example.com ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAQEA0hVqZOvZ7yWgie9OHdTORJVI5fJJoH1yEGamAd5G3werH0z7e9ybtq1mGUeRkJtea7bzru0ISR0EZ9HIONoGYrDmI7S+BiwpDBUKjva4mAsvzzvsy6Ogy/apkxm6Kbcml8u4wjxaOw3NKzKqeBvR3pc+nQVA+SJUZq8D2XBRd4EDUFXeLzwqwen9G7gSLGB1hJkSuRtGRfOHbLUuCKNR8RV82i3JvlSnAwb3MwN0m3WGdlJA8J+5YAg4e6JgSKrsCObZK7W1R6iuyuH1zA+dtAHyDyYVHB4FnYZPL0hgz2PSb9c+iDEiFcT/lT4/dQ+kRW6DYn66lS8peS8zCJ9CSQ==

    And reference the generated known_hosts file in your JSch code.

    If you are on Windows, you can get a Windows build of ssh-keyscan from Win32-OpenSSH project or Git for Windows.

  • Call JSch.getHostKeyRepository().add() to provide the expected host key (e.g. hard-coded, as your other credentials).

    See Creating JSch HostKey instance from a public key in .pub format.

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