Decrypt statements #348
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Decrypt statements #348
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Add these as a separate variant from private key encryptions, since they are created and bounded differently. Since we bound the error term by half the ciphertext modulus, this commit also changes the bounds to be specified by number of bits.
For polynomials with zero coefficients exceeding degree bound
Taking Self was weird. Call sites don't need to be updated as calling associated `Log2::method(x)` is still valid, just a weird thing to enforce.
This would previously give very large norms values for small negative values close to the negative cutoff
Silly mistake but easy to miss: we were storing the message to repeat as a _freshly encoded_ plaintext. The values match, but not the underlying messages! Fix to use the actual plaintext coming out of the decryption, which is not a fresh encoding.
As implemented, this would have almost never been used correctly. The user would have had to ensure that the existing plaintext message had the same plaintext polynomial encoding as the provided ciphertext. This would generally only be true if both were fresh encryptions, in which case this method is not even necessary.
But keep the AS=T debug assertion
Also use u32 over u64, as std::lib does for various "bit length" operations like Shl, log2, et.
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ryanorendorff
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Feb 20, 2024
And fail fast if calculating the modulus overflows
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Support "decryption statements", i.e. statements about ciphertexts that aren't fresh encryptions. These have the same format as symmetric statements in logproof, but the bounds are much more lax as errors can go up to$\Delta/2$ rather than being a fresh noise polynomial.