| CPC H04L 9/3271 (2013.01) [H04L 9/30 (2013.01); H04L 63/0435 (2013.01); H04L 63/0492 (2013.01); H04L 9/14 (2013.01)] | 20 Claims |

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1. An authentication server, comprising:
a processor; and
a memory,
wherein the processor:
transmits an authentication request;
receives a first response that is responsive to the authentication request, the first response comprising a first cryptogram;
generates a first challenge based on the first response;
encrypts the first challenge with a symmetric key;
generates a secret salt that is associated with a transaction;
transmits the first challenge after it has been encrypted and transmits the secret salt along with the encrypted first challenge;
receives a second response that is responsive to the first challenge, the second response comprising a second cryptogram, wherein the second cryptogram is generated using the first challenge in combination with one or more private card keys, and comprises the secret salt;
authenticates the second response by:
decrypting the second cryptogram, and
validating the decrypted second cryptogram using a session key by comparing the secret salt from the second cryptogram with a reference secret salt; and
transmits, to a client device, one or more authentication messages as a result of the validation of the decrypted second cryptogram.
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