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5.12 Shuffling Bytes

The function below addresses the perennial programming quandary: “How do I take good data in string form and painlessly turn it into garbage?” This is not a difficult thing to code for oneself, but the authors of the GNU C Library wish to make it as convenient as possible.

To erase data, use explicit_bzero (see Erasing Sensitive Data); to obfuscate it reversibly, use memfrob (see Obfuscating Data).

Function: char * strfry (char *string) ¶

Preliminary: | MT-Safe | AS-Safe | AC-Safe | See POSIX Safety Concepts.

strfry performs an in-place shuffle on string. Each character is swapped to a position selected at random, within the portion of the string starting with the character’s original position. (This is the Fisher-Yates algorithm for unbiased shuffling.)

Calling strfry will not disturb any of the random number generators that have global state (see Pseudo-Random Numbers).

The return value of strfry is always string.

Portability Note: This function is unique to the GNU C Library. It is declared in string.h.