Rust

SFTP Set Allowed SSH Algorithms

Demonstrates the Chilkat SFtp.SetAllowedAlgorithms method, which configures the exact set of SSH algorithms permitted for the connection. A JsonObject supplies comma-separated allow-lists for the kex, hostKey, cipher, and mac categories. It must be called before Connect.

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

Background: SSH negotiates a mutually supported algorithm from each category at connection time, and pinning that choice makes an application brittle: if a server later drops a weak algorithm or you point the code at a different server, the two sides may fail to agree and the connection breaks. The legitimate reasons to override are a security policy mandating specific algorithms, or a compatibility problem with an old server. Otherwise the safer default is to let the library's ordering evolve as guidance changes.

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// Demonstrates the SFtp.SetAllowedAlgorithms method, which configures the exact set of SSH
// algorithms permitted for the connection.  The only argument is a JsonObject.  It must be
// called before Connect.
// 
// -------------------------------------------------------------------------------------------
// 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 can make 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.
// -------------------------------------------------------------------------------------------

let sftp = chilkat::SFtp::new();

let json = chilkat::JsonObject::new();

// The 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 (encryption):
//   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 (hash):
//   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 key-exchange, host-key, cipher (encryption), and mac (hash) algorithms, in
// order of preference.
let allowed_kex = "curve25519-sha256@libssh.org,ecdh-sha2-nistp256".to_string();
let allowed_host_key = "ssh-ed25519,ecdsa-sha2-nistp256".to_string();
let allowed_cipher = "chacha20-poly1305@openssh.com,aes256-ctr".to_string();
let allowed_mac = "hmac-sha2-256,hmac-sha2-512".to_string();

let _ = json.update_string("kex", &allowed_kex);
let _ = json.update_string("hostKey", &allowed_host_key);
let _ = json.update_string("cipher", &allowed_cipher);
let _ = json.update_string("mac", &allowed_mac);

// Apply the allow-list before connecting.
if sftp.set_allowed_algorithms(&json).is_err() {
    println!("{}", sftp.last_error_text());
    return;
}

let port = 22;
if sftp.connect("sftp.example.com", port).is_err() {
    println!("{}", sftp.last_error_text());
    return;
}

println!("Connected.");

sftp.disconnect();