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.

#include <CkSsh.h>
#include <CkJsonObject.h>

void ChilkatSample(void)
    {
    bool success = false;

    //  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.
    //  -------------------------------------------------------------------------------------------

    CkSsh ssh;

    CkJsonObject json;

    //  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 char *allowed_kex = "curve25519-sha256@libssh.org,ecdh-sha2-nistp256";
    const char *allowed_hostKey = "ssh-ed25519,ecdsa-sha2-nistp256";
    const char *allowed_cipher = "chacha20-poly1305@openssh.com,aes256-ctr";
    const char *allowed_mac = "hmac-sha2-256,hmac-sha2-512";

    json.UpdateString("kex",allowed_kex);
    json.UpdateString("hostKey",allowed_hostKey);
    json.UpdateString("cipher",allowed_cipher);
    json.UpdateString("mac",allowed_mac);

    //  Apply the allow-list.  This must be done before connecting.
    success = ssh.SetAllowedAlgorithms(json);
    if (success == false) {
        std::cout << ssh.lastErrorText() << "\r\n";
        return;
    }

    int port = 22;
    success = ssh.Connect("ssh.example.com",port);
    if (success == false) {
        std::cout << ssh.lastErrorText() << "\r\n";
        return;
    }

    std::cout << "Connected." << "\r\n";

    ssh.Disconnect();
    }