The main motivation for this change is the introduction of the newly
available predicate ed25519_seed_keypair/2, allowing to generate a key
pair from a given seed. In this way, a key pair can be dynamically
generated from (for example) a password, using crypto_password_hash/3
in combination with crypto_data_hkdf/4 to generate the seed. The
advantage of this method is that the private key need not be stored at
all anywhere.
It is not possible to add a corresponding feature to ring, since it is
closed as "not planned": https://github.com/briansmith/ring/issues/1003
I also used this opportunity to move more of the logic to Prolog. We
now have total control of the key pair representation, and I also
changed the representation to conform to the PKCS#8 v2 standard,
something that only later ring versions do, while still being
backwards compatible with tools that produce a wrong representation
including earlier ring versions.
Another great advantage we get from this change is that the Ed25519
predicates now also run on the 32-bit and WASM versions of Scryer.
One use case is to ensure that once/1 is safe to use:
term_si(Goal),
once(Goal)
In such cases, Goal is ground and can yield at most one solution,
therefore once/1 does not remove any solutions.
Example:
?- time(member(X, "abc")).
% CPU time: 0.000s, 1 inference
X = a
; % CPU time: 0.000s, 3 inferences
X = b
; % CPU time: 0.000s, 3 inferences
X = c.
This is an initial step towards addressing #1039.
If reification constraints (such as reified equality) are triggered
here, then they may wish to disable this propagator and remove
attributes from auxiliary variables. If the pexp/3 propagation is
interrupted for that purpose, then the attributes will be
unintentionally reattached by the following fd_put/3 calls in this
propagator. We must ensure that this propagator completely finishes,
so we queue the triggered propagators for later processing.
geq/2 implements propagator activation outside the queue, and thus
should not be used in propagators in the way it was used here.
pexp/3 by itself may not seem particularly important. However, it can
arise by metamorphosis from Var*Var. Example:
?- A#<==> -1#=C*C, C in 0..1.
A = 0, clpz:(C in 0..1).
This addresses #2089.
This addresses all remaining cases from #2083, excepting (//)/2:
?- #\ 1#=(X*X)/0.
clpz:(X in inf..sup).
?- #\ 1#=(X+X)/0.
clpz:(X in inf..sup).
Still remaining:
?- #\ 0#=(Y// -1)/0.
clpz:(-1*Y#=_A).
