(Tcl) Get Web Server's SPKI Fingerprint

Gets the SPKI fingerprint of a web server's certificate.

What is Pinning?

Pinning is the process of associating a host with their expected X509 certificate or public key. Once a certificate or public key is known or seen for a host, the certificate or public key is associated or 'pinned' to the host. If more than one certificate or public key is acceptable, then the program holds a pinset. In this case, the advertised identity must match one of the elements in the pinset. A host or service's certificate or public key can be added to an application at development time, or it can be added upon first encountering the certificate or public key. The former - adding at development time - is preferred since preloading the certificate or public key out of band usually means the attacker cannot taint the pin. ..

Beginning in Chilkat v9.5.0.55, TLS public key pinning is implemented by (1) making it possible to easily get the SPKI fingerprint of a certificate, and (2) adding the TlsPinSet property to classes that can establish TLS connections.

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load ./chilkat.dll

set chilkatGlob [new_CkGlobal]

set success [CkGlobal_UnlockBundle $chilkatGlob "Anything for 30-day trial."]
if {[expr $success != 1]} then {
    puts [CkGlobal_lastErrorText $chilkatGlob]
    delete_CkGlobal $chilkatGlob
    exit
}

set http [new_CkHttp]

#  We're getting the SSL/TLS certificate, so make sure to connect to the SSL/TLS port (443).
# sslCert is a CkCert
set sslCert [CkHttp_GetServerSslCert $http "www.ssllabs.com" 443]
if {[string equal $sslCert "NULL"]} then {
    puts [CkHttp_lastErrorText $http]
    delete_CkGlobal $chilkatGlob
    delete_CkHttp $http
    exit
}

#  The GetSpkiFingerprint method returns the SPKI Fingerprint suitable for use in pinning.
#   (See RFC 7469.)  An SPKI Fingerprint is defined as the output of a known cryptographic hash
#   algorithm whose input is the DER-encoded ASN.1 representation of  the Subject Public Key Info
#  (SPKI) of an X.509 certificate.  The first argument specifies the hash algorithm and may be
#  "sha256", "sha384", "sha512", "sha1", "md2", "md5", "haval", "ripemd128",
#  "ripemd160","ripemd256", or "ripemd320".
#  The second argument specifies the encoding, and may be "base64", "hex",
#  or any of the encoding modes specified at http://www.cknotes.com/chilkat-binary-encoding-list/
#  DN = "Distinguished Name"
puts "SPKI Fingerprint: [CkCert_getSpkiFingerprint $sslCert sha256 base64]"

delete_CkCert $sslCert


delete_CkGlobal $chilkatGlob
delete_CkHttp $http