Regex for unusual Base64 mask

I am looking for a regex that will detect different Base64 masks used in malicious software, like

But my simple regex also matches on repetitive charachters like "ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ"

 [a-zA-Z0-9+/]{64}

Is there a way to match non repeating 64 characters using regex?

Solution

If you're looking to validate you have 64 character and detect that none of them are duplicate characters in any position in the string such as

Good string: 0ABcDEFGHIJKLMNOPQRSTUVWXYZabCdefghijklmnopqrstuvwxyz123456789+/

Bad string 0ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefGhijklmnopqrstuvwxyz123456789+/ because the G appears twice

Then you could use this regex:

^(?=.{64}$)(?!.*?(.)(?=.*?\1))

enter image description here

The regex will return a match if the input string has 64 unique characters.

^ match the beginning of the string
(?=.{64}$) look ahead to ensure there are 64 characters in the string
(?! force negative look ahead which will return false if the interal expression is true
.*? move foreword to any character
(.) capture a single character and place into capture group 1
(?= open positive look ahead to see if any characters after the current character in group 1 is the same
.*? skip any number of characters until you find the next
\1 back reference to the capture group 1 to ensure that character isn't a duplicate
) close positive look ahead
) close the negative look ahead