T 4.36 Mistakes in encoded data

If data which is in an encoded form is changed, it may no longer be possible to decode the data correctly. According to the mode of operation of the encoding routines, this can mean that only a few bytes are decoded incorrectly or that all data following the error is decoded incorrectly. If there is no data backup, this can cause the data to be lost entirely.

Errors in the encoded data can occur in various ways:

• When the encoded data is transmitted, a transmission error occurs that cannot be corrected.

• A permanent error occurs in the storage medium (floppy disk, hard disk).

• A computer virus manipulates the data.

• A third person intentionally manipulates the data, for example by manipulating the encoded data in a few places with an editor.

In serious cases, such as when bits are lost or a large amount of data is altered and the error is propagated, the data cannot be reconstructed even if you know the cryptographic process and the code used for encoding.

An error in the cryptographic codes used can be even more serious. Even if a single bit of a cryptographic code is altered, the result is that all of the data encoded with it can no longer be decoded. If the cryptographic code has no data backup, this data is lost for good.