The invention relates to a method for cryptographic protection of a
data exchange between a first entity (A) and a second entity (B), wherein a signing key pair (KPC) belongs to the first entity (A) and a KEM key pair (KPM) belongs to the second entity (B), the method comprising the following steps: a) signing, by the first entity (A), first data (D1) with a private signing key (SKC) resulting in a first signature (SI1); b) providing the first entity (A) with a first symmetric key (K1) and a first
ciphertext (CT1) using an encapsulation procedure (Encap) of a
key encapsulation mechanism, where the encapsulation procedure (Encap) calculates a first
shared secret (SS1) and the first
ciphertext (CT1) from the public KEM key (PKM); c) encrypting, by the first entity (A), at least the first signature (SI1) with an
encryption procedure (AEAD) which uses the first symmetric key (K1), resulting in a first piece of information (ENC1) comprising the encrypted first signature and data corresponding to the first data (D1); d) transmitting, by the first entity (A), the first
ciphertext (CT1) and the first piece of information (ENC1) to the second entity (B); e) providing the second entity (B) with the first symmetric key (K1), using a decapsulation procedure (Decap) of the
key encapsulation mechanism, where the decapsulation procedure (Decap) calculates the first
shared secret (SS1) from the first ciphertext (CT1) and the private KEM key (SKM); f) decrypting, by the second entity (B), at least the encrypted first signature with a decryption procedure (AEAD-1) which uses the first symmetric key (K1), resulting in the first data (D1) and the first signature (SI1); g) verifying, by the second entity (B), the first signature (SI1) decrypted in step f) with the public signing key (PKC).