This PR adds four config options to configure whether and how to load
indutny/elliptic: use_indutny_elliptic, external_indutny_elliptic,
indutny_elliptic_path and indutny_elliptic_fetch_options.
Also:
- Use tweetnacl.js instead of indutny/elliptic for curve25519 key generation
- Don't initialize indutny's curve25519, improving performance when using that curve
- Verify NIST signatures using Web Crypto instead of indutny/elliptic when not streaming
- Move KeyPair.sign/verify to ecdsa.js
- Move KeyPair.derive to ecdh.js
- Move keyFromPrivate and keyFromPublic to a new indutnyKey.js file
* Various FIXME tags are removed
* In curve.js:
- webCrypto/nodeCrypto fallback bug is fixed
- Curve25519 has keyType ecdsa (won't be used for signing, but technically can be)
- webGenKeyPair is simplifed
* In base64.js:
- documentation added and arguments simplified
* In ecdsa.js and eddsa.js:
- hash_algo is now at least as strong as the default curve hash
- simplified the code by moving webSign/nodeSign and webVerify/nodeVerify to live in key.js (ht @ismaelbej)
* In message.js:
- in decryptSessionKey, loops break once a key packet is decrypted
* In key.js:
- getPreferredHashAlgorithm returns the best hash algorithm
- enums are used for curve selection
