Curve25519 Signatures and Key Agreement

curve25519-js provides a JavaScript implementation of Curve25519, facilitating both digital signatures and X25519 Diffie-Hellman key agreement. The current stable version is 0.0.4. While its release cadence appears infrequent, with a significant rewrite in 2019, it serves as a functional library for cryptographic operations. A key differentiator is its ability to use a single X25519 key for both signing and key agreement, a feature that distinguishes it from standard Ed25519 implementations which typically use separate key types or require explicit conversion. This is achieved by embedding and extracting a sign bit into the signature during the process. The library is derived from TweetNaCl.js and is suitable for environments where direct Curve25519 operations are needed.