dependencies: configure subtle features for std only

Cargo.toml

@@ -12,7 +12,7 @@ license = "MIT OR Apache-2.0"
 # no-alloc, no-std
 cfg-if = "1.0"
 hex = { version ="=0.4.2", default-features = false }
-subtle = "2.5"
+subtle = { version="2.5", default-features = false }
 tracing-subscriber = { version = "0.3", default-features = false }
 zeroize = { version = "1.7", default-features = false }
 # no-std
@@ -39,7 +39,7 @@ once_cell = { version= "1.8", optional = true, default-features = false }
 [features]
 default = ["arkworks"]
 alloc = ["once_cell/alloc", "tracing-subscriber/alloc", "zeroize/alloc"]
-std = ["alloc", "tracing/std", "anyhow/std", "tracing-subscriber/std", "zeroize/std", "once_cell/std", "num-bigint/std", "hex/std"]
+std = ["alloc", "tracing/std", "anyhow/std", "tracing-subscriber/std", "zeroize/std", "once_cell/std", "num-bigint/std", "hex/std", "subtle/std"]
 parallel = ["ark-ff/parallel", "ark-ec/parallel", "ark-groth16/parallel", "ark-std/parallel", "ark-r1cs-std/parallel"]
 # TODO: eventually, feature-gate all arkworks deps behind this feature.
 arkworks = ["std", "ark-std", "ark-ec", "ark-ff", "ark-serialize", "ark-bls12-377", "ark-ed-on-bls12-377"]