(Tcl) Get RSA Key Modulus from .cer or .key

Demonstrates how to get the RSA key modulus from either the certificate (.cer) or RSA key (.key). OpenSSL commands to do the same would be:

openssl x509 -inform DER -in "test.cer"  -modulus -noout 

openssl pkcs8 -inform DER -in​ "test.key"​ -outform PEM -passin pass:"12345​678a​"
   | openssl rsa -inform PEM -modulus -noout 

Note: This example requires Chilkat v11.0.0 or greater.

Chilkat Tcl Extension Downloads Chilkat Tcl Extension Downloads

load ./chilkat.dll

set success 0

set privKey [new_CkPrivateKey]

set password "12345678a"
set success [CkPrivateKey_LoadPkcs8EncryptedFile $privKey "qa_data/certs/test_12345678a.key" $password]
if {$success == 0} then {
    puts [CkPrivateKey_lastErrorText $privKey]
    delete_CkPrivateKey $privKey
    exit
}

set xml [new_CkXml]

CkXml_LoadXml $xml [CkPrivateKey_getXml $privKey]

# The XML contains the parts of the key in base64.
puts "Private Key XML:"
puts [CkXml_getXml $xml]

# We can get the base64 modulus like this:
set modulus [CkXml_getChildContent $xml "Modulus"]
puts "base64 modulus = $modulus"

# To convert to hex:
set binDat [new_CkBinData]

CkBinData_AppendEncoded $binDat $modulus "base64"
set hexModulus [CkBinData_getEncoded $binDat "hex"]
puts "hex modulus = $hexModulus"

# Now get the modulus from the cert:
set cert [new_CkCert]

set success [CkCert_LoadFromFile $cert "qa_data/certs/test_12345678a.cer"]
if {$success == 0} then {
    puts [CkCert_lastErrorText $cert]
    delete_CkPrivateKey $privKey
    delete_CkXml $xml
    delete_CkBinData $binDat
    delete_CkCert $cert
    exit
}

# The cert contains the public key, which is composed of the
# modulus + exponent (for RSA keys).
set pubKey [new_CkPublicKey]

CkCert_GetPublicKey $cert $pubKey

CkXml_LoadXml $xml [CkPublicKey_getXml $pubKey]
puts "Public Key XML:"
puts [CkXml_getXml $xml]

# Proceed in the same way as before....
set modulus [CkXml_getChildContent $xml "Modulus"]
puts "base64 modulus = $modulus"

# To convert to hex:
CkBinData_Clear $binDat
CkBinData_AppendEncoded $binDat $modulus "base64"
set hexModulus [CkBinData_getEncoded $binDat "hex"]
puts "hex modulus = $hexModulus"

delete_CkPrivateKey $privKey
delete_CkXml $xml
delete_CkBinData $binDat
delete_CkCert $cert
delete_CkPublicKey $pubKey