Delphi ActiveX

Use RSAES-OAEP Padding for Encrypted Email

Demonstrates the Chilkat Email.OaepPadding property, which selects the RSA encryption scheme used when encrypting email. The default is false, which selects RSAES PKCS1-v1_5; setting it to true selects RSAES-OAEP. This affects the RSA key-encryption step used for S/MIME encryption — it does not change the symmetric content-encryption algorithm chosen by Pkcs7CryptAlg. This example enables OAEP padding.

Background: Recall that S/MIME encrypts the message body with a one-time symmetric key, then encrypts that key with RSA. "Padding" is how the key bytes are formatted before RSA is applied. The older PKCS1-v1_5 padding has known theoretical weaknesses, while RSAES-OAEP adds randomness and a hash-based construction that is provably more secure and is the modern recommendation. Both endpoints must agree, so a recipient's software has to support OAEP to read the message.

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var
email: TChilkatEmail;

begin
//  Demonstrates the Email.OaepPadding property, which selects the RSA encryption scheme
//  used when encrypting email.  The default is false (RSAES PKCS1-v1_5).  Set it to true
//  to use RSAES-OAEP.  This affects only the RSA key-encryption step, not the symmetric
//  content-encryption algorithm selected by Pkcs7CryptAlg.

email := TChilkatEmail.Create(Self);
email.Subject := 'Encrypted with RSAES-OAEP';
email.Body := 'This message uses OAEP padding for the RSA key encryption.';

//  Use RSAES-OAEP instead of the older PKCS1-v1_5 scheme.
email.OaepPadding := 1;

Memo1.Lines.Add('OaepPadding = ' + IntToStr(Ord(email.OaepPadding)));