RSA DES hybrid (FinTS) (RDH)

The RSA DES method(RDH) is an asymmetric hybrid encryption for securing confidentiality between clients and servers. The RDH procedure exists in various variants and is used in FinTS, among others.

In the different RDH variants, the message is encrypted with the symmetric Triple DES( 3DES) encryption, always using a new key generated by a random generator. This key for the message is encrypted with a public RSA key of the recipient and transmitted together with the encrypted message. During transmission, the sender of the message selects this random session key with a key length of 128 bits and applies the DDV procedure to the message using this key. The key itself is encrypted with the recipient's public RSA key and placed in front of the encrypted data. The recipient of the message decrypts the session key with his secret RSA key.

In addition to RDH-1, there are also variants RDH-2, RDH-3 and RDH-4, which can be used as optional encryption methods in the Financial Transaction Service (FinTS).

For the RDH-2, RDH-3 and RDH-4 variants, the key length, which is still 768 bits for RDH-1, has been extended to 1024 bits to 2048 bits.