Build regex patterns for search through b64 encoded text without decoding.
Project description
Base64 Regex
Search through base64 encoding without decoding.
Usage
Building a regex
To build a regex pattern for matching a specific string through base64, use the
Segment.as_regex()
function:
from b64_regex.recoder import Segment
segment = Segment(b"string-to-search")
segment.as_regex()
# Output:
# (?:c3RyaW5nLXRvLXNlYXJja[A-P]|[HXn3]N0cmluZy10by1zZWFyY2[g-j]|[BFJNRVZdhlptx159]zdHJpbmctdG8tc2VhcmNo)
Slightly more advanced patterns are supported via combination of segments with
normal regex. The B64_CHARGROUP
variable contains [a-zA-Z0-9\/\+]
for
convenience.
from b64_regex.recoder import Segment, B64_CHARGROUP
start_segment = Segment(b"patternPrefix(")
end_segment = Segment(b")patternSuffix")
full_regex = f"{start_segment.as_regex()}{B64_CHARGROUP}+{end_segment.as_regex()}"
# Output:
# (?:cGF0dGVyblByZWZpeC[g-j]|[HXn3]BhdHRlcm5QcmVmaXgo|[BFJNRVZdhlptx159]wYXR0ZXJuUHJlZml4K[A-P])[a-zA-Z0-9\/\+]+(?:KXBhdHRlcm5TdWZmaX[g-j]|[CSiy]lwYXR0ZXJuU3VmZml4|[AEIMQUYcgkosw048]pcGF0dGVyblN1ZmZpe[A-P])
Decoding matches
As around 33% of the matches are going to be misaligned by 2 or 4 bits, decoding might need the prefixing of one or two b64 tokens to yield the right results.
The decode_all_alignments
function decodes the provided string with each bit
alignment and strips the prefixed extra data from the result. It however is not
able to know which result is correct, and instead returns all three:
from b64_regex.recoder import decode_all_alignments
match = "HBhdHRlcm5QcmVmaXgoZm9vLWJhci1jb250ZW50YWFhYWFhKXBhdHRlcm5TdWZmaXh"
for x in decode_all_alignments(match):
print(x)
# Output:
# b'\x1c\x18]\x1d\x19\\\x9b\x94\x1c\x99Y\x9a^\n\x19\x9b\xdb\xcbX\x98\\\x8bX\xdb\xdb\x9d\x19[\x9d\x18XXXXXJ\\\x18]\x1d\x19\\\x9b\x94\xddY\x99\x9a^'
# b'patternPrefix(foo-bar-contentaaaaaa)patternSuffix'
# b'\xc1\x85\xd1\xd1\x95\xc9\xb9A\xc9\x95\x99\xa5\xe0\xa1\x99\xbd\xbc\xb5\x89\x85\xc8\xb5\x8d\xbd\xb9\xd1\x95\xb9\xd1\x85\x85\x85\x85\x85\x84\xa5\xc1\x85\xd1\xd1\x95\xc9\xb9M\xd5\x99\x99\xa5\xe1'
Future work
It should be possible to translate some regex features to work within the b64 context (such as string length selectors / character repeats).
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