A cross system secure logon in a target system by using a first authentication system and a second authentication system. A correct password may be valid on the first authentication system and the second authentication system. An aspect includes receiving an input password, generating a first hash key by using the first authentication system, and/or generating a second hash key by using the second authentication system, wherein each authentication system uses a system unique non-collision free hash algorithm. Further, in one aspect, comparing the first hash key with a first predefined hash key of the correct password stored in the first authentication system, and/or comparing the second hash key with a second predefined hash key of the correct password stored in the second authentication system. Furthermore, granting access to the target system based on at least one of the comparisons.