Delphi DLL

Get RSA Key Modulus from .cer or .key

See more Certificates Examples

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 

or

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

Delphi DLL

uses
    Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
    Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, BinData, PrivateKey, Xml, PublicKey, Cert;

...

procedure TForm1.Button1Click(Sender: TObject);
var
success: Boolean;
privKey: HCkPrivateKey;
password: PWideChar;
xml: HCkXml;
modulus: PWideChar;
binDat: HCkBinData;
hexModulus: PWideChar;
cert: HCkCert;
pubKey: HCkPublicKey;

begin
success := False;

privKey := CkPrivateKey_Create();

password := '12345678a';
success := CkPrivateKey_LoadPkcs8EncryptedFile(privKey,'qa_data/certs/test_12345678a.key',password);
if (success = False) then
  begin
    Memo1.Lines.Add(CkPrivateKey__lastErrorText(privKey));
    Exit;
  end;

xml := CkXml_Create();
CkXml_LoadXml(xml,CkPrivateKey__getXml(privKey));

// The XML contains the parts of the key in base64.
Memo1.Lines.Add('Private Key XML:');
Memo1.Lines.Add(CkXml__getXml(xml));

// We can get the base64 modulus like this:
modulus := CkXml__getChildContent(xml,'Modulus');
Memo1.Lines.Add('base64 modulus = ' + modulus);

// To convert to hex:
binDat := CkBinData_Create();
CkBinData_AppendEncoded(binDat,modulus,'base64');
hexModulus := CkBinData__getEncoded(binDat,'hex');
Memo1.Lines.Add('hex modulus = ' + hexModulus);

// Now get the modulus from the cert:
cert := CkCert_Create();

success := CkCert_LoadFromFile(cert,'qa_data/certs/test_12345678a.cer');
if (success = False) then
  begin
    Memo1.Lines.Add(CkCert__lastErrorText(cert));
    Exit;
  end;

// The cert contains the public key, which is composed of the
// modulus + exponent (for RSA keys).
pubKey := CkPublicKey_Create();
CkCert_GetPublicKey(cert,pubKey);

CkXml_LoadXml(xml,CkPublicKey__getXml(pubKey));
Memo1.Lines.Add('Public Key XML:');
Memo1.Lines.Add(CkXml__getXml(xml));

// Proceed in the same way as before....
modulus := CkXml__getChildContent(xml,'Modulus');
Memo1.Lines.Add('base64 modulus = ' + modulus);

// To convert to hex:
CkBinData_Clear(binDat);
CkBinData_AppendEncoded(binDat,modulus,'base64');
hexModulus := CkBinData__getEncoded(binDat,'hex');
Memo1.Lines.Add('hex modulus = ' + hexModulus);

CkPrivateKey_Dispose(privKey);
CkXml_Dispose(xml);
CkBinData_Dispose(binDat);
CkCert_Dispose(cert);
CkPublicKey_Dispose(pubKey);

end;