Add a "not" operator for hex bytes #1676
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plusvic
reviewed
Apr 5, 2022
| @@ -171,6 +171,21 @@ the length of the variable chunks, however, this is not always the case. In some | |||
| circumstances you may need to define strings with chunks of variable content and | |||
| length. In those situations you can use jumps instead of wild-cards: | |||
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| .. code-block:: yara | |||
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The new example has been inserted at the wrong position in the text. It says:
In those situations you can use jumps instead of wild-cards:
And the sentence is followed by NotExample instead of JumpExample.
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Should be fixed now.
plusvic
approved these changes
Apr 6, 2022
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When specifying hex strings, we run across cases where we want to specify that a byte in not a specific value.
eg.
$want = " { 81 FE ?? ?? ?? ?? 7F } $dont_want = " { 81 FE ?? ?? ?? 00 7F }This pull request adds a not operator (~) on bytes so you could specify:
$want_and_dont_want = " { 81 FE ?? ?? ?? ~00 7F }This seems to be pretty straightforward and useful. At the moment only individual bytes can be negated, but it could be easily expanded to cover negated masked bytes such a
~7?More complex would be expressing as a general construct so you can have things like
~(00 | 01)but I'm not sure how far we want to go in expanding hex strings to be a complete regex language in it's own right.