Tcl

Verify and Pin the FTPS Server Certificate

Demonstrates the certificate-verification properties RequireSslCertVerify, TlsPinSet, and the read-only SslServerCertVerified.

Background: By default a TLS connection is not rejected merely because certificate-chain verification fails, so RequireSslCertVerify = true is the important hardening step — it makes an expired, unsigned, or untrusted certificate abort the connection. TlsPinSet adds public-key pinning on top: the handshake fails unless the server's SPKI fingerprint matches one you configured, defending against a mis-issued certificate that would otherwise validate. Pinning supplements verification rather than replacing it. SslServerCertVerified reports the outcome.

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Tcl


load ./chilkat.dll

set success 0

set ftp [new_CkFtp2]

CkFtp2_put_Hostname $ftp "ftp.example.com"
CkFtp2_put_Username $ftp "myFtpLogin"

CkFtp2_put_AuthTls $ftp 1

#  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.
CkFtp2_put_Password $ftp "myPassword"

#  Reject the connection if the server certificate cannot be verified (expired, bad signature,
#  untrusted chain, etc.).  The default is 0, which does not reject on verification
#  failure -- set 1 for security.
CkFtp2_put_RequireSslCertVerify $ftp 1

#  Optionally pin the server's public key.  If none of the configured SPKI fingerprints matches,
#  the TLS handshake fails.  Pinning supplements normal verification; it does not replace it.
CkFtp2_put_TlsPinSet $ftp "sha256//YLh1dUR9y6Kja30RrAn7JKnbQG/uEtLMkBgFF2Fuihg="

set success [CkFtp2_Connect $ftp]
if {$success == 0} then {
    puts [CkFtp2_lastErrorText $ftp]
    delete_CkFtp2 $ftp
    exit
}

#  SslServerCertVerified reports whether the certificate chain was successfully verified.
if {CkFtp2_get_SslServerCertVerified $ftp} then {
    puts "The server certificate was verified."
}

set success [CkFtp2_Disconnect $ftp]
if {$success == 0} then {
    puts [CkFtp2_lastErrorText $ftp]
    delete_CkFtp2 $ftp
    exit
}


delete_CkFtp2 $ftp