k256/p256: use new SignPrimitive API; add BlindedScalar
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tarcieri
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Updates both crates with the `SignPrimitive` changes from RustCrypto/signatures#107. These changes removed the `masking_scalar` from the trait, and replaced it with trait bounds that make it possible to substitute a blinded scalar. In the `p256` crate (which is the only one that presently implements a variable-time inversion) the `masking_scalar` is replaced with a `BlindedScalar` type that implements the previous blinded inversion. The implementation it uses (including `Scalar::invert_vartime`) could potentially be made generic and extracted into the `elliptic-curve` crate, allowing it to be used with any curve which implements the arithmetic primitives used in the blinded inversion implementation. However, for now, this PR leaves it in `p256`, and therefore at least has feature parity with the old implementation.
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Codecov Report
@@ Coverage Diff @@
## master #99 +/- ##
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- Coverage 53.08% 52.83% -0.26%
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Files 18 19 +1
Lines 3415 3435 +20
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+ Hits 1813 1815 +2
- Misses 1602 1620 +18
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tarcieri
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Jul 28, 2020
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| fn scalar_blinding() { | ||
| let vector = &ECDSA_TEST_VECTORS[0]; | ||
| let d = Scalar::from_bytes(vector.d.try_into().unwrap()).unwrap(); | ||
| let k = Scalar::from_bytes(vector.k.try_into().unwrap()).unwrap(); | ||
| let k_blinded = BlindedScalar::new(k, &mut OsRng); | ||
| let sig = d | ||
| .try_sign_prehashed(&k_blinded, GenericArray::from_slice(vector.m)) | ||
| .unwrap(); | ||
|
|
||
| assert_eq!(vector.r, sig.r().as_slice()); | ||
| assert_eq!(vector.s, sig.s().as_slice()); | ||
| } |
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FYI @nickray, here's the proposed alternative for masking_scalar.
I had it take an RNG argument directly, but we could also add an API to construct one from two Scalar values you generate however you want (perhaps that could be new, and the RNG-based one could be generate)
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Updates both crates with the
SignPrimitivechanges from RustCrypto/signatures#107.These changes removed the
masking_scalarargument from the trait, and replaced it with trait bounds that make it possible to substitute a blinded scalar.In the
p256crate (which is the only one that presently implements a variable-time inversion) themasking_scalaris replaced with aBlindedScalartype that implements the previous blinded inversion.The implementation it uses (including
Scalar::invert_vartime) could potentially be made generic and extracted into theelliptic-curvecrate, allowing it to be used with any curve which implements the arithmetic primitives used in the blinded inversion implementation.However, for now, this PR leaves it in
p256, and therefore at least has feature parity with the old implementation.