These were originally added in 32da4c7d50
to implement Scalar negation in terms of multiply-add.
But we have a full implementation of scalar arithmetic now, so it's not
necessary to keep the constants around.
The public-facing types with arithmetic operations are:
- `Scalar`s
- `ExtendedPoint`s
- `RistrettoPoint`s
For these types we define operators with all combinations of borrowed and
non-borrowed inputs, to avoid forcing API consumers to write extra ampersands.
Since all of the operations involved with these types are expensive relative to
the cost of an unnecessary copy, this isn't a big deal.
The `MontgomeryPoint` struct isn't included in the above because it's only
useful for scalar multiplication.
This commit is based on work by @UnlawfulMonad.
This commit defines a Scalar to hold an integer representing an element of
Z/lZ. Applications like X/Ed25519 that care about the bit-patterns of the
scalars they use can set a specific bit-pattern using the `from_bits`
constructor. Applications that want to treat scalars as integers mod l can use
the `from_bytes_mod_order` constructor. Either way, the constructor ensures
that the integer representing each Scalar is bounded by 2^255 so that the high
bit is set. This means that any Scalar object is always safe to use for scalar
multiplication, while maintaining compatibility with both the Ristretto
use-case and the X/Ed25519 usecase.
This reverts commit 804dab8924, reversing
changes made to 5d15ca77ff.
This is due to a (previously undocumented) contract on the behaviours of
(potentially unreduced mod \ell) "packed" scalars w.r.t. to the manner in which
their bytes are interpreted.
Upon documentation fixes and corresponding fixes being made on top of the
floodyberry/optimized_scalar branch, this revert will again be reverted and then
the additional changes merged (à la
file:///usr/share/doc/git/html/howto/revert-a-faulty-merge.html).
Signed-off-by: Isis Lovecruft <isis@patternsinthevoid.net>
Make the 2 digit, `_10`, the first argument to more closely match the
Haskell code in the source article. Align the code into columns to
further clarify the patterns.
