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Related to Curve25519 Curve25519 seems to be secure so far. Yet, you have to remind yourself that Dr. Bernstein specified Curve25519 for key-exchange. Meaning: key-generation, transaction signing, and verification are somewhat different beasts – you might want to cross-check on that before jumping toward Curve25519. Sure, Curve25519-java supports signing… ...


Support for this has now (2014-08-05) been added to Sodium. Implement ed25519 -> curve25519 keys conversion Look at test/default/ed25519_convert.c for some example code.


Trevor Perrin wrote a library doing exactly that. Explanation can be found on in the curves mailing list archives. To convert a Curve25519 public key $x_C$ into an Ed25519 public key $y_E$, with a Ed25519 sign bit of $0$: $$y_E = \frac{x_C - 1}{x_C + 1} \mod 2^{255}-19$$ The Ed25519 private key may need to be adjusted to match the sign bit of $0$: if ...

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