(Delphi DLL) Understanding a few ECDSA Public Key Formats

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Describes a few ECDSA public key formats.

Chilkat for Delphi Downloads Chilkat non-ActiveX DLL for Delphi Chilkat ActiveX DLL for Delphi * The examples here use the non-ActiveX DLL.

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

...

procedure TForm1.Button1Click(Sender: TObject);
var
success: Boolean;
sbPem: HCkStringBuilder;
pubKey1: HCkPublicKey;
sbHex: HCkStringBuilder;
numReplaced: Integer;
bdKey: HCkBinData;
pubKey2: HCkPublicKey;

begin
// Here we have the output of the following openssl command:  openssl ec -in key.pem -pubout -text

// Private-Key: (256 bit)
// priv:
//     0e:63:25:8a:73:3c:71:b6:c0:e7:a3:0f:94:b9:74:
//     e0:be:bd:46:18:be:40:7e:66:9e:21:99:85:0e:ed:
//     87:2d
// pub:
//     04:5d:1a:4f:d9:bd:49:9e:e4:fd:55:2c:0d:ea:6d:
//     b1:66:64:7a:71:91:13:63:86:fe:ca:94:d4:47:51:
//     39:66:ff:43:d5:62:de:f2:f2:41:3c:2e:3f:95:18:
//     2d:23:f7:e7:8e:75:19:3b:c6:50:fb:d9:90:f5:e8:
//     12:b7:b8:6a:43
// ASN1 OID: prime256v1
// NIST CURVE: P-256
// writing EC key
// -----BEGIN PUBLIC KEY-----
// MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEXRpP2b1JnuT9VSwN6m2xZmR6cZET
// Y4b+ypTUR1E5Zv9D1WLe8vJBPC4/lRgtI/fnjnUZO8ZQ+9mQ9egSt7hqQw==
// -----END PUBLIC KEY-----

// The public key is shown in two different formats.
// The first is this:

// pub:
//     04:5d:1a:4f:d9:bd:49:9e:e4:fd:55:2c:0d:ea:6d:
//     b1:66:64:7a:71:91:13:63:86:fe:ca:94:d4:47:51:
//     39:66:ff:43:d5:62:de:f2:f2:41:3c:2e:3f:95:18:
//     2d:23:f7:e7:8e:75:19:3b:c6:50:fb:d9:90:f5:e8:
//     12:b7:b8:6a:43

// It is the ANSI X9.63 format.
// 65-bytes are the uncompressed public key (04 || X || Y) 

// This is the same public key, but in PEM format

// -----BEGIN PUBLIC KEY-----
// MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEXRpP2b1JnuT9VSwN6m2xZmR6cZET
// Y4b+ypTUR1E5Zv9D1WLe8vJBPC4/lRgtI/fnjnUZO8ZQ+9mQ9egSt7hqQw==
// -----END PUBLIC KEY-----

// It contains ASN.1 that more explicitly identifies the key type.
// 
// SEQUENCE (2 elem)
//   SEQUENCE (2 elem)
//     OBJECT IDENTIFIER 1.2.840.10045.2.1 ecPublicKey (ANSI X9.62 public key type)
//     OBJECT IDENTIFIER 1.2.840.10045.3.1.7 prime256v1 (ANSI X9.62 named elliptic curve)
//   BIT STRING (520 bit) 000001000101110100011010010011111101100110111101010010011001111011100...

// PEM format can be loaded into a Chilkat public key object like this:

sbPem := CkStringBuilder_Create();
CkStringBuilder_Append(sbPem,'-----BEGIN PUBLIC KEY-----' + #13#10);
CkStringBuilder_Append(sbPem,'MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEXRpP2b1JnuT9VSwN6m2xZmR6cZET' + #13#10);
CkStringBuilder_Append(sbPem,'Y4b+ypTUR1E5Zv9D1WLe8vJBPC4/lRgtI/fnjnUZO8ZQ+9mQ9egSt7hqQw==' + #13#10);
CkStringBuilder_Append(sbPem,'-----END PUBLIC KEY-----' + #13#10);

pubKey1 := CkPublicKey_Create();
success := CkPublicKey_LoadFromString(pubKey1,CkStringBuilder__getAsString(sbPem));
if (success = False) then
  begin
    Memo1.Lines.Add(CkPublicKey__lastErrorText(pubKey1));
    Exit;
  end;

// The X9.63 format can be loaded like this:
sbHex := CkStringBuilder_Create();
CkStringBuilder_Append(sbHex,'04:5d:1a:4f:d9:bd:49:9e:e4:fd:55:2c:0d:ea:6d:');
CkStringBuilder_Append(sbHex,'b1:66:64:7a:71:91:13:63:86:fe:ca:94:d4:47:51:');
CkStringBuilder_Append(sbHex,'39:66:ff:43:d5:62:de:f2:f2:41:3c:2e:3f:95:18:');
CkStringBuilder_Append(sbHex,'2d:23:f7:e7:8e:75:19:3b:c6:50:fb:d9:90:f5:e8:');
CkStringBuilder_Append(sbHex,'12:b7:b8:6a:43');

// Get rid of the ":" chars.
numReplaced := CkStringBuilder_Replace(sbHex,':','');

// We'll need to convert hex to base64..
bdKey := CkBinData_Create();
CkBinData_AppendEncoded(bdKey,CkStringBuilder__getAsString(sbHex),'hex');

pubKey2 := CkPublicKey_Create();
success := CkPublicKey_LoadFromString(pubKey2,CkBinData__getEncoded(bdKey,'base64'));
if (success = False) then
  begin
    Memo1.Lines.Add(CkPublicKey__lastErrorText(pubKey2));
    Exit;
  end;

// Let's get the key in pubKey2 as PEM.
// It should be idential to the PEM above.
Memo1.Lines.Add(CkPublicKey__getPem(pubKey2,True));

// Here's the output.  You can see it's the same as the PEM above..

// -----BEGIN PUBLIC KEY-----
// MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEXRpP2b1JnuT9VSwN6m2xZmR6cZET
// Y4b+ypTUR1E5Zv9D1WLe8vJBPC4/lRgtI/fnjnUZO8ZQ+9mQ9egSt7hqQw==
// -----END PUBLIC KEY-----

CkStringBuilder_Dispose(sbPem);
CkPublicKey_Dispose(pubKey1);
CkStringBuilder_Dispose(sbHex);
CkBinData_Dispose(bdKey);
CkPublicKey_Dispose(pubKey2);

end;