Visual Basic 6.0

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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Visual Basic 6.0

Dim success As Long
success = 0

'  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.

Dim ftp As New ChilkatFtp2

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 = 1

'  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","ftp.example.com"

success = ftp.Connect()
If (success = 0) Then
    Debug.Print ftp.LastErrorText
    Exit Sub
End If

Debug.Print "Connected; server certificate met the requirement."

success = ftp.Disconnect()
If (success = 0) Then
    Debug.Print ftp.LastErrorText
    Exit Sub
End If