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.