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Fix quadratic-time PEM post-boundary check #937

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Fix quadratic-time PEM post-boundary check #937

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10 changes: 6 additions & 4 deletions lib/Crypto/IO/PEM.py
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Original file line number Diff line number Diff line change
Expand Up @@ -129,10 +129,12 @@ def decode(pem_data, passphrase=None):
raise ValueError("Not a valid PEM pre boundary")
marker = m.group(1)

# Verify Post-Encapsulation Boundary
r = re.compile(r"-----END (.*)-----\s*$")
m = r.search(pem_data)
if not m or m.group(1) != marker:
# Verify Post-Encapsulation Boundary.
# The marker is already known from the pre-boundary, so the boundary can be
# matched directly. Searching for it with r"-----END (.*)-----\s*$" was
# quadratic in len(pem_data): every "-----END " is a start position for the
# search, and the greedy (.*) backtracks the whole remainder at each one.
if not pem_data.rstrip().endswith("-----END %s-----" % marker):
raise ValueError("Not a valid PEM post boundary")

# Removes spaces and slit on lines
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