During the login process is very important to check if fingerprint of server is valid. To verify server please use fingerprints below. All servers in one datacenter have the same RSA, DSA and ECDSA key.

Ostrava data center (du4):

ECDSA, SHA256 (du4) 9YvWE2h459dMcLWcLcD1DsrxTjqqMLD16eiSYXBVX9k 
ED25519, SHA256 (du4) L0AFWpSsuq+SFl2QBip4aFJEuG3JEnUxczomfEywYvc

Jihlava data center (du5):

ECDSA, SHA256 (du5) YB7YnmuMktwsFxVe5qdzy2bLU9y+0yowEcpZp82P4nk

If the key does not match, stop connecting to the server and contact us at: support@cesnet.cz If the key does not match, stop connecting to the server and contact us at: support@cesnet.cz