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man pages section 3: Extended Library Functions, Volume 2

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Updated: July 2017



isencrypt - determine whether a buffer of characters is encrypted


cc  [flag]... [file]... -lgen [library]...

int isencrypt(const char *fbuf, size_t ninbuf);


isencrypt() uses heuristics to determine whether a buffer of characters is encrypted. It requires two arguments: a pointer to an array of characters and the number of characters in the buffer.

isencrypt() assumes that the file is not encrypted if all the characters in the first block are ASCII characters. If there are non-ASCII characters in the first ninbuf characters, and if the setlocale() LC_CTYPE category is set to C or ascii, isencrypt() assumes that the buffer is encrypted

If the LC_CTYPE category is set to a value other than C or ascii, then isencrypt() uses a combination of heuristics to determine if the buffer is encrypted. If ninbuf has at least 64 characters, a chi-square test is used to determine if the bytes in the buffer have a uniform distribution; if it does, then isencrypt() assumes the buffer is encrypted. If the buffer has less than 64 characters, a check is made for null characters and a terminating new-line to determine whether the buffer is encrypted.

Return Values

If the buffer is encrypted, 1 is returned; otherwise, zero is returned.


See attributes(5) for descriptions of the following attributes:


See Also

setlocale(3C), attributes(5)


When compiling multithreaded applications, the _REENTRANT flag must be defined on the compile line. This flag should only be used in multithreaded applications.