Currently, OpenSSL does not have the required
`EVP_PKEY_get1_ED(25519|448)` functions, hence EdDSA has been partially
implemented and disabled. Once OpenSSL 3.0.0 is out and the `openssl`
crates implements the bindings to those functions, full EdDSA
implementation could be done and activated.
Conditional compilation has been implemented using `rustc-cfg`
instructions rather than features so it can be activated from the build
script depending on whether or not the cryptographic library supports
Ed25519 and Ed448.
7c664b1f1b
Rodolphe Breard
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