Enhance Side Channel resistance of TPM2 RSA Decryption Wrapper #4429
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Unfortunately, the ESAPI call already introduces some side channel leaks by allocating the result buffer only if the decryption succeeds. Co-Authored-By: René Meusel <[email protected]>
randombit
approved these changes
Nov 7, 2024
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The TPM2 Wrapper of RSA decryption had a bug with incompatible types while setting
valid_mask.During the fix up we noticed that the rest of the function did not run in constant time and may present an oracle on padding failures. Thanks to @phwork for finding this.
This PR enhances the wrapper's side channel resistance in that regard.
Unfortunately, the ESAPI call already introduces some side channel leaks by allocating the result buffer only if the decryption succeeds. This is by specification (Section 14.3.1), as the call to the underlying RSA decryption function returns an error code if unpadding fails.
@randombit opinions are welcome, we are not sure how big of an issue this is and if our enhancement makes much sense.