SSH Set Allowed Algorithms

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Demonstrates explicitly setting the algorithms allowed during SSH connection negotiation. A JsonObject supplies comma-separated allow-lists for the kex, hostKey, cipher, and mac categories, in order of preference, and is applied before connecting.

Important: You typically should not set allowed algorithms explicitly. By default Chilkat orders algorithms according to best practices and accounts for known vulnerabilities such as the Terrapin attack.

const std = @import("std");
const chilkat = @import("chilkat");

pub fn main(init: std.process.Init) !void {
    const alloc = init.arena.allocator();

    // This example requires the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    // Demonstrates explicitly setting the algorithms allowed during SSH connection negotiation.
    //
    // -------------------------------------------------------------------------------------------
    // Note: You typically should NOT explicitly set allowed algorithms.
    // By default, Chilkat orders algorithms according to best practices and accounts for known
    // vulnerabilities such as the "Terrapin Attack".  Hard-coding algorithms makes an application
    // brittle over time: if a server later changes its allowed algorithms, or if you connect to a
    // different server, the client and server may fail to agree on a mutually supported set.
    // -------------------------------------------------------------------------------------------

    const ssh = try chilkat.Ssh.init();
    defer ssh.deinit();

    const json = try chilkat.JsonObject.init();
    defer json.deinit();

    // Algorithms supported by Chilkat, by category:
    //
    // Key-exchange:  curve25519-sha256, curve25519-sha256@libssh.org, ecdh-sha2-nistp256,
    //   ecdh-sha2-nistp384, ecdh-sha2-nistp521, diffie-hellman-group14-sha256,
    //   diffie-hellman-group16-sha512, diffie-hellman-group18-sha512,
    //   diffie-hellman-group-exchange-sha256, diffie-hellman-group1-sha1,
    //   diffie-hellman-group14-sha1, diffie-hellman-group-exchange-sha1
    //
    // Host key:  ssh-ed25519, ecdsa-sha2-nistp256, ecdsa-sha2-nistp384, ecdsa-sha2-nistp521,
    //   rsa-sha2-256, rsa-sha2-512, ssh-rsa, ssh-dss
    //
    // Cipher:  chacha20-poly1305@openssh.com, aes128-ctr, aes256-ctr, aes192-ctr, aes128-cbc,
    //   aes256-cbc, aes192-cbc, aes128-gcm@openssh.com, aes256-gcm@openssh.com, twofish256-cbc,
    //   twofish128-cbc, blowfish-cbc
    //
    // MAC:  hmac-sha2-256, hmac-sha2-512, hmac-sha2-256-etm@openssh.com,
    //   hmac-sha2-512-etm@openssh.com, hmac-sha1-etm@openssh.com, hmac-sha1, hmac-ripemd160,
    //   hmac-sha1-96, hmac-md5

    // List the allowed algorithms for each category, in order of preference.
    const allowed_kex = "curve25519-sha256@libssh.org,ecdh-sha2-nistp256";
    const allowed_host_key = "ssh-ed25519,ecdsa-sha2-nistp256";
    const allowed_cipher = "chacha20-poly1305@openssh.com,aes256-ctr";
    const allowed_mac = "hmac-sha2-256,hmac-sha2-512";

    json.updateString("kex", allowed_kex) catch {};
    json.updateString("hostKey", allowed_host_key) catch {};
    json.updateString("cipher", allowed_cipher) catch {};
    json.updateString("mac", allowed_mac) catch {};

    // Apply the allow-list.  This must be done before connecting.
    ssh.setAllowedAlgorithms(json) catch {
        std.debug.print("{s}\n", .{try ssh.getLastErrorText(alloc)});
        return;
    };

    const port = 22;
    ssh.connect("ssh.example.com", port) catch {
        std.debug.print("{s}\n", .{try ssh.getLastErrorText(alloc)});
        return;
    };

    std.debug.print("Connected.\n", .{});

    ssh.disconnect();
}