A key fragment generator accepts a key string, such as from a key string generator, and produces a plurality of key fragments that can be entered by a human with a lower likelihood of error than if the human attempted to enter the original key string. A key defragmenter accepts a plurality of entered key fragments, reconstitutes the original key string from the entered key fragments and, optionally, provides the reconstituted key string to a software package or other license manager. The key fragment generator can produce "friendly" key fragments that are easier for humans to read and enter than the arbitrary character strings that characterize typical key strings. The key fragment generator can produce "error-detectable" key fragments. If an error-detectable key fragment is entered incorrectly, the key defragmenter can generate an error message and permit a user to enter the key fragment again. The key fragment generator can produce "error-correctable" key fragments. If an error-correctable key fragment is entered incorrectly, the key defragmenter can generate an error message that describes the nature of the error or that draws a user's attention to a portion of the key fragment that the user entered incorrectly. The error message can include a "hint" related to one or more confusable characters that were entered incorrectly.