(Objective-C) SSH Set Allowed Algorithms

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Demonstrates how to explicitly set the algorithms allowed in the SSH connection protocol.

Note: This example requires Chilkat v9.5.0.99 or greater.

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#import <CkoSsh.h>
#import <CkoJsonObject.h>
#import <NSString.h>

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

BOOL success;
CkoSsh *ssh = [[CkoSsh alloc] init];

CkoJsonObject *json = [[CkoJsonObject alloc] init];

// Here are the algorithms supported by Chilkat at the time this example was written (14-June-2024)

// ---------------------------
// SSH Key-Exchange Algorithms
// ---------------------------
// 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

// ---------------------------
// SSH Host Key Algorithms
// ---------------------------
// ssh-ed25519
// ecdsa-sha2-nistp256
// ecdsa-sha2-nistp384
// ecdsa-sha2-nistp521
// rsa-sha2-256
// rsa-sha2-512
// ssh-rsa
// ssh-dss

// ---------------------------
// SSH Cipher Algorithms
// ---------------------------
// 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

// ---------------------------
// SSH MAC Algorithms
// ---------------------------
// 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

// Specify the allowed key-exchange, host-key, cipher (i.e. encryption), and mac (i.e. hash) algorithms allowed, in the order of preference.
// -------------------------------------------------------------------------------------------------------------------------------------------
// Note: You typically should NOT explicitly set allowed algorithms.
// By default, Chilkat orders algorithms according to best practices, and pays attention to vulnerabilities such as the "Terrapin Attack".
// Hard-coding algorthims can make your application brittle and prone to breaking over a long period of time,
// if a server (at some point in the future) changes its allowed algorithms, or if you connect to a different server,
// such that the client (Chilkat) and server cannot find a set of mutually agreed-upon algorithms.
// -------------------------------------------------------------------------------------------------------------------------------------------
NSString *allowed_kex = @"curve25519-sha256@libssh.org,ecdh-sha2-nistp256";
NSString *allowed_hostKey = @"ssh-ed25519,ecdsa-sha2-nistp256";
NSString *allowed_cipher = @"chacha20-poly1305@openssh.com,aes256-ctr";
NSString *allowed_mac = @"hmac-sha2-256,hmac-sha2-512";

[json UpdateString: @"kex" value: allowed_kex];
[json UpdateString: @"hostKey" value: allowed_hostKey];
[json UpdateString: @"cipher" value: allowed_cipher];
[json UpdateString: @"mac" value: allowed_mac];
[ssh SetAllowedAlgorithms: json];

int port = 22;
success = [ssh Connect: @"example.com" port: [NSNumber numberWithInt: port]];
if (success != YES) {
    NSLog(@"%@",ssh.LastErrorText);
    return;
}

NSLog(@"%@",@"Connected.");

// ....
// ....