Establishment of forward secrecy during digest authentication

1 . A method for establishing forward secrecy during digest access authentication, the method being performed by a client device, the method comprising:

performing digest access authentication with a server device, the digest access authentication comprising:

sending a first request towards the server device for accessing a resource;

receiving a first response from the server device, wherein the first response comprises a challenge and a public component, pk, of an asymmetric key pair, (pk, sk), for a key exchange with the server device, and information identifying a key encapsulation mechanism;

calculating, using a digest algorithm, a response parameter based at least on the challenge and the public component of the asymmetric key pair;

calculating ciphertext and a shared secret by subjecting the public component to the key encapsulation mechanism identified in the first response;

sending a second request towards the server device for accessing the resource, wherein the second request comprises the calculated response parameter and the ciphertext; and

receiving a second response from the server device, wherein the second response indicates successful digest access authentication with the server device.

2 . The method according to claim 1 , wherein, in the first response, the public component, pk, is provided in its own WWW-Authenticate header field or its own Proxy-Authenticate header field.

3 . The method according to claim 1 , wherein the asymmetric key pair, (pk, sk) is based on finite-field Diffie-Hellman key exchange.

4 . The method according to claim 1 , wherein the response parameter is calculated from the challenge and using the public component, pk, and based on knowledge of a client password.

5 . The method according to claim 1 , wherein the first response further comprises at least one of:

a network authenticator token,

further information identifying further parameters for calculating the response parameter; or

at least two challenges, and indications of as many different digest algorithms, one digest algorithm being associated with each challenge, wherein the response parameter is calculated using one of the at least two challenges using the digest algorithm associated with said one of the at least two challenges, and wherein the response parameter is indicative of all the different digest algorithms.

6 . The method according to claim 5 , wherein the response parameter is calculated upon having verified the network authenticator token and/or wherein, when the further information is identified, the response parameter is calculated based on a result value, wherein the result value is calculated from the challenge, and wherein the response parameter further is calculated using the public component, pk, and a local long-term secret.

7 . The method according to claim 1 , wherein the key encapsulation mechanism is based on key exchange using any of: finite-field Diffie-Hellman, elliptic curve Diffie-Hellman, RSA, lattice-based cryptography, code-based key cryptography, isogeny-based cryptography key exchange.

8 . A client device for establishing forward secrecy during digest access authentication, the client device comprising processing circuitry configured to cause the client device to:

perform digest access authentication with a server device, the processing circuitry being configured to cause the client device to, as part of performing the digest access authentication:

send a first request towards the server device for accessing a resource;

receive a first response from the server device, wherein the first response comprises a challenge and a public component, pk, of an asymmetric key pair, (pk, sk), for a key exchange with the server device, and information identifying a key encapsulation mechanism;

calculate, using a digest algorithm, a response parameter based at least on the challenge and the public component of the asymmetric key pair;

calculate ciphertext and a shared secret by subjecting the public component to the key encapsulation mechanism identified in the first response;

send a second request towards the server device for accessing the resource, wherein the second request comprises the calculated response parameter and the ciphertext; and

receive a second response from the server device, wherein the second response indicates successful digest access authentication with the server device.