If information is encrypted and the encrypted data is subsequently changed, it may no longer be possible to decrypt it properly. Depending on the mode of operation of the encryption routines, this may result in just a few bytes being decrypted incorrectly, or all of the data in question. If there is no backup, such data will be lost.

An error in the cryptographic keys used may be even more critical. Changing even a single bit of a cryptographic key may make it impossible to decrypt the data encrypted using the key.