The error java.security.InvalidKeyException: Invalid key format usually occurs when you are trying to use an invalid key or an incorrectly formatted key to perform some cryptographic operation, such as encrypting or decrypting data.

To fix this error, you need to make sure that you are using a valid and correctly formatted key. Some possible causes of this error and their solutions are:

• You are using an incorrect key length: Make sure that the key you are using has the correct length for the cryptographic algorithm you are using.
• You are using an invalid key format: Make sure that the key you are using is in the correct format for the cryptographic algorithm you are using. For example, if you are using an RSA key, it should be in PEM format.
• You are using an incorrect key type: Make sure that the key you are using is of the correct type for the cryptographic algorithm you are using. For example, if you are using an AES key, it should be a secret key, not a public key.

If you are still experiencing this error after trying the above solutions, it might be caused by some other problem, such as a bug in your code or an issue with your Java installation. In this case, you may need to debug your code or check your Java installation to find the root cause of the problem.