A method for securely checking an electronic ticket, in particular an electronic bus and/or railway ticket, wherein the electronic ticket is stored on a first mobile terminal device allocated to an end consumer, and the ticket is checked using a second terminal device allocated to a ticket inspector or to a control system, wherein the method comprises the following steps: - sending a request message from the second terminal device to the first terminal device via a first communication channel; - sending a response message from the first terminal device to the second terminal device via a second communication channel, the response message being signed by the first terminal device, and the second communication channel either being identical with the first communication channel or different from the first communication channel; - verifying the signed response message by the second terminal device; and - confirming the authenticity of the response message by the second terminal device, if the second terminal device was previously able to verify the authenticity of the signature; wherein - the request message comprises a random number of the length L, generated by the second terminal device, where L >=1, and the response message includes a representation of the random number generated by the second terminal device, encrypted using a private key of the first terminal device; - the response message includes a digital certificate that originates from the service provider that has issued the electronic ticket or from an entity classified as trustworthy by the service provider; - the response message comprises an electronic ticket which, besides the ticket information, also comprises a first digital identifier of the first terminal device, and that the electronic ticket comprises a digital signature of the service provider; - in addition to the electronic ticket, the response message comprises a second digital identifier of the first terminal device generated by the first terminal device; and - the second terminal device confirms the authenticity of the response message only if the first identifier contained in the electronic ticket and the second identifier generated by the first terminal device are identical. - sending a request message from the second terminal device to the first terminal device via a first communication channel; - sending a response message from the first terminal device to the second terminal device via a second communication channel, the response message being signed by the first terminal device, and the second communication channel either being identical with the first communication channel or different from the first communication channel; - verifying the signed response message by the second terminal device; and - confirming the authenticity of the response message by the second terminal device, if the second terminal device was previously able to verify the authenticity of the signature; wherein - the request message comprises a random number of the length L, generated by the second terminal device, where L >=1, and the response message includes a representation of the random number generated by the second terminal device, encrypted using a private key of the first terminal device; - the response message includes a digital certificate that originates from the service provider that has issued the electronic ticket or from an entity classified as trustworthy by the service provider; - the response message comprises an electronic ticket which, besides the ticket information, also comprises a first digital identifier of the first terminal device, and that the electronic ticket comprises a digital signature of the service provider; - in addition to the electronic ticket, the response message comprises a second digital identifier of the first terminal device generated by the first terminal device; and - the second terminal device confirms the authenticity of the response message only if the first identifier contained in the electronic ticket and the second identifier generated by the first terminal device are identical.