A method for authenticating a first computer system to a second computer system for cryptographically secured communication between the two computer systems , wherein the method comprises: • providing an authentication file containing authentication data for authentication of the first computer system , wherein the authentication file is provided by a third computer system , from which the authentication data are retrievable via a network , wherein a certificate issued for the first computer system comprises a reference for identifying the authentication data for authentication of the first computer system , wherein the authenticity and integrity of the corresponding reference are secured by the certificate signature comprised by the certificate , and wherein the authentication data contain details relating to the holder of the certificate , • receiving, by the third computer system via the network , a read request from the second computer system for reading the authentication data, wherein the read request identifies the authentication data by using the reference , • in response to the receipt of the read request, sending the requested authentication data to the second computer system by the third computer system via the network for authentication of the first computer system , wherein the certificate further comprises a cryptographic parameter for establishing a cryptographically secured connection between the first and the second computer system , wherein the method further comprises issuing a replacement certificate with altered cryptographic parameters for replacing the previous certificate of the first computer system , whilst the authentication file is retained, unaltered, by the third computer system for retrieval via the network . • providing an authentication file containing authentication data for authentication of the first computer system , wherein the authentication file is provided by a third computer system , from which the authentication data are retrievable via a network , wherein a certificate issued for the first computer system comprises a reference for identifying the authentication data for authentication of the first computer system , wherein the authenticity and integrity of the corresponding reference are secured by the certificate signature comprised by the certificate , and wherein the authentication data contain details relating to the holder of the certificate , • receiving, by the third computer system via the network , a read request from the second computer system for reading the authentication data, wherein the read request identifies the authentication data by using the reference , • in response to the receipt of the read request, sending the requested authentication data to the second computer system by the third computer system via the network for authentication of the first computer system , wherein the certificate further comprises a cryptographic parameter for establishing a cryptographically secured connection between the first and the second computer system , wherein the method further comprises issuing a replacement certificate with altered cryptographic parameters for replacing the previous certificate of the first computer system , whilst the authentication file is retained, unaltered, by the third computer system for retrieval via the network . <EOS>