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Fix for CVE-2020-25658 - #1
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Fix sybrenstuvel#165: CVE-2020-25658 - Bleichenbacher-style timing oracle Use as many constant-time comparisons as practical in the `rsa.pkcs1.decrypt` function. `cleartext.index(b'\x00', 2)` will still be non-constant-time. The alternative would be to iterate over all the data byte by byte in Python, which is several orders of magnitude slower. Given that a perfect constant-time implementation is very hard or even impossible to do in Python [1], I chose the more performant option here. [1]: https://securitypitfalls.wordpress.com/2018/08/03/constant-time-compare-in-python/
This was referenced Nov 9, 2026
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Fix sybrenstuvel#165: CVE-2020-25658 - Bleichenbacher-style timing oracle
Use as many constant-time comparisons as practical in the
rsa.pkcs1.decryptfunction.cleartext.index(b'\x00', 2)will still be non-constant-time. The alternative would be to iterate over all the data byte by byte in Python, which is several orders of magnitude slower. Given that a perfect constant-time implementation is very hard or even impossible to do in Python 1, I chose the more performant option here.