This gives the caller more control about whether the state should
be cleaned (= should be considered secret). Moreover, it gives the
caller the possibility to clean a hash struct without finalizing it.
All of the invocations of secp256k1_memclear() operate on stack
memory and happen after the function is done with the memory object.
This commit replaces existing memset() invocations and also adds
secp256k1_memclear() to code locations where clearing was missing;
there is no guarantee that this commit covers all code locations
where clearing is necessary.
Co-Authored-By: isle2983 <isle2983@yahoo.com>
The previous code is correct and harmless to initialize an array with a
non-terminated character sequence using a string literal.
However, it requires exactly specifying the array size, which can be
cumbersome.
Also, GCC-15 may issue the -Wunterminated-string-initialization warning.
[1]
Fix both issues by using array initialization. This refactoring commit
does not change behavior.
[1] Example warning:
src/modules/schnorrsig/main_impl.h:48:46: error: initializer-string for array of 'unsigned char' is too long [-Werror=unterminated-string-initialization]
48 | static const unsigned char bip340_algo[13] = "BIP0340/nonce";
| ^~~~~~~~~~~~~~~
By providing an uppercase variant of these verification functions, it is
better visible that it is test code and surrounding `#ifdef VERIFY`
blocks can be removed (if there is no other code around that could
remain in production mode), as they don't serve their purpose any more.
At some places intentional blank lines are inserted for grouping and
better readadbility.
Now that the `VERIFY_CHECK` compiles to empty in non-VERIFY mode, blocks
that only consist of these macros don't need surrounding `#ifdef VERIFY`
conditions anymore.
At some places intentional blank lines are inserted for grouping and
better readadbility.
As suggested in issue #1381, this will make things simpler and
improve code readability, as we don't need to force omitting of
evaluations on a case-by-case basis anymore and hence can remove
lots of `#ifdef VERIFY`/`#endif` lines (see next commit). Plus,
VERIFY_CHECK behaves now identical in both non-VERIFY and coverage mode,
making the latter not special anymore and hopefully decreasing
maintenance burden. The idea of "side-effect safety" is given up.
Note that at two places in the ellswift module void-casts of return
values have to be inserted for non-VERIFY builds, in order to avoid
"variable ... set but not used [-Wunused-but-set-variable]"
warnings.
When configured with `--disable-module-ecdh --enable-module-recovery`, then
`./tests 64 81af32fd7ab8c9cbc2e62a689f642106` fails with
```
src/modules/ellswift/tests_impl.h:396: test condition failed: secp256k1_memcmp_var(share32_bad, share32a, 32) != 0
```
This tests verifies that changing the `party` bit of the
`secp256k1_ellswift_xdh` function results in a different share. However, that's
not the case when the secret keys of both parties are the same and this is
actually what happens in the observed test failure. The keys can be equal in
this test case because they are created by the `random_scalar_order_test`
function whose output is not uniformly random (it's biased towards 0).
This commit restores the assummption that the secret keys differ.
The scheme implemented is described below, and largely follows the paper
"SwiftEC: Shallue–van de Woestijne Indifferentiable Function To Elliptic Curves",
by Chavez-Saab, Rodriguez-Henriquez, and Tibouchi
(https://eprint.iacr.org/2022/759).
A new 64-byte public key format is introduced, with the property that *every*
64-byte array is an encoding for a non-infinite curve point. Each curve point
has roughly 2^256 distinct encodings. This permits disguising public keys as
uniformly random bytes.
The new API functions:
* secp256k1_ellswift_encode: convert a normal public key to an ellswift 64-byte
public key, using additional entropy to pick among the many possible
encodings.
* secp256k1_ellswift_decode: convert an ellswift 64-byte public key to a normal
public key.
* secp256k1_ellswift_create: a faster and safer equivalent to calling
secp256k1_ec_pubkey_create + secp256k1_ellswift_encode.
* secp256k1_ellswift_xdh: x-only ECDH directly on ellswift 64-byte public keys,
where the key encodings are fed to the hash function.
The scheme itself is documented in secp256k1_ellswift.h.
