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.

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

BOOL success = NO;

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

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

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

//  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.
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];

//  Apply the allow-list.  This must be done before connecting.
success = [ssh SetAllowedAlgorithms: json];
if (success == NO) {
    NSLog(@"%@",ssh.LastErrorText);
    return;
}

int port = 22;
success = [ssh Connect: @"ssh.example.com" port: [NSNumber numberWithInt: port]];
if (success == NO) {
    NSLog(@"%@",ssh.LastErrorText);
    return;
}

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

[ssh Disconnect];