A method implemented by a network node in a mobile network of validating a subscription concealed identifier, which network node is a Unified Data Management, UDM, function or another Subscription Identifier De-concealing Function, SIDF, comprising: receiving a message including the subscription concealed identifier, wherein the subscription concealed identifier is generated by a user equipment; obtaining a first set of encryption parameters used to generate the subscription concealed identifier wherein the first set of encryption parameters is obtained from the received message and verifying that the first set of encryption parameters is valid before de-concealing the subscription concealed identifier, wherein the subscription concealed identifier is determined to be invalid when the first set of encryption parameters is not in use; when determined that the first set of encryption parameters is valid, de-concealing the subscription concealed identifier to obtain subscription information associated with a subscription, wherein the subscription concealed identifier is de-concealed using the first set of encryption parameters and verifying that the result of de-concealing is valid before obtaining the second set of encryption parameters; when determined that the de-concealing result is valid, obtaining a second set of encryption parameters associated with the subscription using the subscription information wherein the second set of encryption parameters is obtained from a subscriber profile associated to the user equipment; and validating the subscription concealed identifier based on the second set of encryption parameters, wherein validating the subscription concealed identifier comprises determining whether the subscription concealed identifier is valid by comparing the first set of encryption parameters to the second set of encryption parameters, and any one out of: - determining that the subscription concealed identifier is valid when the comparison results in a match, or - determining that the subscription concealed identifier is invalid when the comparison does not result in a match. receiving a message including the subscription concealed identifier, wherein the subscription concealed identifier is generated by a user equipment; obtaining a first set of encryption parameters used to generate the subscription concealed identifier wherein the first set of encryption parameters is obtained from the received message and verifying that the first set of encryption parameters is valid before de-concealing the subscription concealed identifier, wherein the subscription concealed identifier is determined to be invalid when the first set of encryption parameters is not in use; when determined that the first set of encryption parameters is valid, de-concealing the subscription concealed identifier to obtain subscription information associated with a subscription, wherein the subscription concealed identifier is de-concealed using the first set of encryption parameters and verifying that the result of de-concealing is valid before obtaining the second set of encryption parameters; when determined that the de-concealing result is valid, obtaining a second set of encryption parameters associated with the subscription using the subscription information wherein the second set of encryption parameters is obtained from a subscriber profile associated to the user equipment; and validating the subscription concealed identifier based on the second set of encryption parameters, wherein validating the subscription concealed identifier comprises determining whether the subscription concealed identifier is valid by comparing the first set of encryption parameters to the second set of encryption parameters, and any one out of: - determining that the subscription concealed identifier is valid when the comparison results in a match, or - determining that the subscription concealed identifier is invalid when the comparison does not result in a match. - determining that the subscription concealed identifier is valid when the comparison results in a match, or - determining that the subscription concealed identifier is invalid when the comparison does not result in a match.