Objective-C

Require Specific FTPS Server Certificate Fields

Demonstrates the Chilkat Ftp2.SetSslCertRequirement method, which adds a required match against the FTP server certificate. The first argument selects the certificate field (such as SubjectCN or IssuerCN) and the second is the required value. It is a void method; a non-matching certificate causes the connection to fail.

Background: Standard TLS validation confirms a certificate is trusted and valid for the hostname, but it does not guarantee you reached the specific server you expect — a form of pinning closes that gap. Requiring a certificate field to match a known value rejects any certificate that does not, defending against a mis-issued or substituted certificate even if it would otherwise pass validation. Multiple requirements can be added, and all must be satisfied.

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Objective-C

#import <CkoFtp2.h>

BOOL success = NO;

//  Demonstrates the Ftp2.SetSslCertRequirement method, which adds a required match against the FTP
//  server certificate.  The 1st argument selects the certificate field and the 2nd is the required
//  value.  It is a void method.

CkoFtp2 *ftp = [[CkoFtp2 alloc] init];

ftp.Hostname = @"ftp.example.com";
ftp.Username = @"myFtpLogin";

//  Normally you would not hard-code the password in source.  You should instead obtain it
//  from an interactive prompt, environment variable, or a secrets vault.
ftp.Password = @"myPassword";

//  Use explicit FTPS (AUTH TLS) on the standard FTP port.
ftp.AuthTls = YES;

//  Require that the server certificate's subject common name matches an expected value.  If the
//  presented certificate does not match, the TLS connection fails.  Supported fields include
//  SubjectDN, SubjectCN, IssuerDN, IssuerCN, and others.
[ftp SetSslCertRequirement: @"SubjectCN" value: @"ftp.example.com"];

success = [ftp Connect];
if (success == NO) {
    NSLog(@"%@",ftp.LastErrorText);
    return;
}

NSLog(@"%@",@"Connected; server certificate met the requirement.");

success = [ftp Disconnect];
if (success == NO) {
    NSLog(@"%@",ftp.LastErrorText);
    return;
}