use SHA256 instead of XOR to combine x509pop nonces #562
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XOR allows for a malicious agent to fake key possession by finding an existing set of plaintext + signature generated by the key and choosing a nonce that will produce the plaintext when XOR'd with the server nonce. Swapping to SHA256 prevents the attacker from choosing a nonce that hashes to the plaintext. Signed-off-by: Andrew Harding <azdagron@gmail.com>
azdagron
requested review from
amartinezfayo,
evan2645,
MarcosDY,
martincapello and
walmav
as code owners
evan2645
approved these changes
Aug 20, 2018
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XOR allows for a malicious agent to fake key possession by finding an
existing set of plaintext + signature generated by the key and choosing
a nonce that will produce the plaintext when XOR'd with the server
nonce.
Swapping to SHA256 prevents the attacker from choosing a nonce that
hashes to the plaintext.
Many thanks to @enricoschiattarella for pointing this out.