Starcos 3.7 C3 Smart Cards - Information on encryption support in Microsoft Outlook
Giesecke&Devrient only supports the RSAES-OAEP encryption scheme for the new Starcos 3.7 C3 smart cards. This fact results from the requirements and recommendations of the international standards listed below.
In the S/MIME encryption environment in Microsoft Outlook, there is an incompatibility when decrypting received messages: the email can be encrypted without any problems, but it cannot be decrypted on the recipient's side with a Starcos 3.7 C3 smart card.
This behavior is caused by the procedure that S/MIME encryption applies. The message content is encrypted symmetrically (e.g. AES) and in order to read the message, it is necessary to first decrypt the symmetric key of the message using the private key. It is at this stage that the private key stored on the smart card is used, and here incompatibility between Outlook/Windows S/MIME and the smart card may occur.
In practice, this problem in Outlook is caused by the fact that it uses the fixed, now deprecated, RSAES-PKCS#1 v1.5 scheme for symmetric key encryption and does not allow switching to RSAES-OAEP.
International cryptographic standards:
- PKCS #1 v2.2 / RFC 8017
Defines RSAES-OAEP as the recommended scheme for RSA encryption and replaces the older, now deprecated RSAES-PKCS1-v1_5 scheme. - ISO/IEC 18033-2
International standard for asymmetric encryption algorithms, which lists RSAES-OAEP as a secure encryption scheme. - NIST SP 800-56B
American standard published by NIST that specifies the secure use of RSA for key exchange and explicitly recommends the use of OAEP padding. - NIST SP 800-57
A standard for cryptographic key management that considers RSAES-OAEP to be an approved and secure scheme when the key length and hash function are set correctly.
