Configure Regular Expressions

Consider the best practices for using regular expression matches.

Use predefined data patterns instead of regular expressions
. Use
Enterprise DLP
predefined data patterns instead of regular expressions where possible. Data patterns are more efficient than regular expressions because the predefined data patterns are tuned for accuracy and the data is validated. For example, if you want to search for social security numbers, use the US Social Security Number (SSN) data pattern instead of a regular expression.
Use regular expressions sparingly
. Regular expressions can be computationally expensive. If you add a regular expression condition, observe the system for 1 hour for efficient performance. Make sure that the system doesn’t slow down and there are no false positives.
Test regular expressions
. If you implement regular expression matching, consider using a third-party tool to test the regular expressions before you enable the policy rules. The recommended tool is RegexBuddy. Another good tool for testing your regular expressions is RegExr. If your expression is incorrect, the service can’t match or will match incorrectly.

Understand expression terminology.

Expression Terminology:

Term	Description
Literal	A literal is any character you use in a search or matching expression, for example, to find dlp in Enterprise DLP , dlp is a literal string - each character plays a part in the search, it’s literally the string we want to find.
Metacharacter	A metacharacter is one or more special characters that have a unique meaning and are NOT used as literals in the search expression, for example, the character < > (caret) is a metacharacter.
Regular Expression	This term describes the search expression data pattern that you will be using to search in Enterprise DLP .
Escape Sequence	An escape sequence is a way of indicating that you want to use one of the metacharacters as a literal. In a regular expression an escape sequence involves placing the metacharacter \ (backslash) in front of the metacharacter that you use as a literal, for example, if you want to find ( dlp ) in Enterprise DLP then use the search expression \(dlp\), and if you want to find \\file in the target string c:\\file then you would need to use the search expression \\\\file (each \ to search for a literal (there are 2) that is preceded by an escape sequence \).

Understand expression constructs.

Enterprise DLP

implements Perl Compatible Regular Expressions (PCRE) syntax for policy rule condition matching.

Enterprise DLP

provides some common reference constructs for writing regular expressions to match or exclude characters in content.

Regular expression constructs:

Construct	Description
.	A dot, any single character, except newline (line ending, end of line, or line break) characters.
\	Escape the next character (the character becomes a normal/literal character.)
\d	Any digit (0-9.)
\s	Any white space.
\W	Any word character (a-z, A-Z, 0-9.)
\D	Anything other than a digit.
\S	Anything other than a white space.
[ ]	Elements inside brackets are a character class (for example, [abc] matches 1 character [a. b. or c.]
^	At the beginning of a character class, negates it (for example, [^abc] matches anything except (a, b, or c.)
$	At the end of a character class, or before newline at the end.
+	Following a regular expression means 1 or more (for example, \d+ means 1 more digit.)
?	Following a regular expression means 0 or 1 (for example, \d? means 1 or no digit.)
*	Following a regular expression means any number (for example \d* means 0, 1, or more digits.)
(?i)	At the beginning of a regular expression makes it case-insensitive (regular expressions are case-sensitive by default.)
( )	Groups regular expressions together.
(?u)	Makes a period ( . ) match to even newline characters.
|	Means OR (for example, A|B means regular expression A or regular expression B.)

Understand expression qualifiers.

Quantifiers can be used to specify the number or length that part of a pattern should match or repeat. A quantifier will bind to the expression group to its immediate left.

Regular expression quantifiers:

Quantifier	Description
*	Match 0 or more times.
+	Match 1 or more times.
?	Match 1 or 0 times.
{n}	Match exactly n times.
{n, }	Match at least n times.
{n, m}	Match at least n but not more than m times.

Enter one regular expression per line, up to 100 lines of expressions.

(

Weighted expressions only

): Assign a regular expression for each line entry between

-9999

(lowest importance) to

9999

(highest importance) by entering the regular expression, the delimiter, and the weight score. You must enter a weight threshold score of one (1) of more.

(

Optional

) Customize your delimiter.

By default, the delimiter for all weighted regular expressions is semicolon ( ; ). You can customize your delimiter to copy and paste existing expressions instead of entering them manually. A delimiter is used to specify separate strings of data when configuring regular expressions. For example, you can configure a weighted regular expression using a delimiter to separate the string of text you’re matching from the weight threshold value. If you have large amounts of existing expressions to match, you can customize your delimiter to copy and paste the expressions instead of entering them manually. A delimiter can be any nonalphanumeric, nonbackslash, non-whitespace character.

Regular expression delimiters:

Delimiter	Note
;	Semicolon — If the delimiter isn’t customized, the semicolon is the default delimiter in Enterprise data loss prevention (DLP) .
:	Colon.
|	Pipe.
/	Forward Slash — If the delimiter needs to be matched inside the pattern it must be escaped using a backslash ( \ ). If the delimiter appears often inside the pattern, it’s a good idea to choose another delimiter to increase readability.
+	Plus — Include phrase for matching.
-	Minus — Ignore phrase for matching.
#	Hash — Can be used to denote a number.
~	Tilde
{ } Curly	Brackets are used to find a range of characters. Bracket style delimiters don’t need to be escaped when they’re used as meta characters within the pattern, but they must be escaped when they’re used as literal characters.
[ ] Square
( ) Parenthesis
< > Caret