A method executed at a network node, the method comprising: generating a common public key G pk and a master secret key G msk; assigning, to a first user equipment UE 1, a first set of one or more pseudonym identifications {PID 1} corresponding to a real identity RID 1 of the first user equipment UE 1, the common public key G pk and a first private key U sk1 specific to the first user equipment UE 1, wherein the first private key U sk1 is generated based on the real identity RID 1 of the first user equipment, the common public key G pk and the master secret key G msk, and wherein the first private key U sk1 is used by the first user equipment UE 1 for authenticating communication with a second user equipment UE 2; assigning, to the second user equipment UE 2, a second set of one or more pseudonym identifications {PID 2} corresponding to a real identity RID 2 of the second user equipment UE 2, the common public key G pk and a second private key U sk2 specific to the second user equipment UE 2, wherein the second private key U sk2 is generated based on a real identity RID 2 of the second user equipment UE 2, the common public key G pk and the master secret key G msk, wherein the second private key U sk2 is used by the second user equipment UE 2 for authenticating communication with the first user equipment UEi; receiving a request for establishing a communication session between the first user equipment UE 1 with a first pseudonym identification PID 1 and the second user equipment UE 2 with a second pseudonym identification PID 2; and generating a first intermediate key Hinti for the first user equipment UE 1 based on the common public key G pk and a second secret key SS 2 shared between the second user equipment UE 2 and the network node, and a second intermediate key Hint 2 for the second user equipment UE 2 based on the common public key G pk and a first secret key SS 1 shared between the first user equipment UE 1 and the network node, wherein the first and second intermediate keys Hint 1, Hint 2 are used by the first and second user equipments UE 1, UE 2 respectively to generate a session key K UE1-UE2 based on respectively at least one of the first intermediate key Hinti and the second intermediate key Hint 2, the session key K UE1-UE2 to be used by the first and second user equipments UE 1, UE 2 for securing the communication session upon the first and second user equipments UE 1, UE 2 successfully authenticate each other based on the common public key G pk and on the first and second private keys U sk1 and U sk2. generating a common public key G pk and a master secret key G msk; assigning, to a first user equipment UE 1, a first set of one or more pseudonym identifications {PID 1} corresponding to a real identity RID 1 of the first user equipment UE 1, the common public key G pk and a first private key U sk1 specific to the first user equipment UE 1, wherein the first private key U sk1 is generated based on the real identity RID 1 of the first user equipment, the common public key G pk and the master secret key G msk, and wherein the first private key U sk1 is used by the first user equipment UE 1 for authenticating communication with a second user equipment UE 2; assigning, to the second user equipment UE 2, a second set of one or more pseudonym identifications {PID 2} corresponding to a real identity RID 2 of the second user equipment UE 2, the common public key G pk and a second private key U sk2 specific to the second user equipment UE 2, wherein the second private key U sk2 is generated based on a real identity RID 2 of the second user equipment UE 2, the common public key G pk and the master secret key G msk, wherein the second private key U sk2 is used by the second user equipment UE 2 for authenticating communication with the first user equipment UEi; receiving a request for establishing a communication session between the first user equipment UE 1 with a first pseudonym identification PID 1 and the second user equipment UE 2 with a second pseudonym identification PID 2; and generating a first intermediate key Hinti for the first user equipment UE 1 based on the common public key G pk and a second secret key SS 2 shared between the second user equipment UE 2 and the network node, and a second intermediate key Hint 2 for the second user equipment UE 2 based on the common public key G pk and a first secret key SS 1 shared between the first user equipment UE 1 and the network node, wherein the first and second intermediate keys Hint 1, Hint 2 are used by the first and second user equipments UE 1, UE 2 respectively to generate a session key K UE1-UE2 based on respectively at least one of the first intermediate key Hinti and the second intermediate key Hint 2, the session key K UE1-UE2 to be used by the first and second user equipments UE 1, UE 2 for securing the communication session upon the first and second user equipments UE 1, UE 2 successfully authenticate each other based on the common public key G pk and on the first and second private keys U sk1 and U sk2.