Function tor_llcrypto::pk::keymanip::convert_ed25519_to_curve25519_private

pub fn convert_ed25519_to_curve25519_private(keypair: &Keypair) -> StaticSecret

👎Deprecated since 0.6.0: ed25519_to_curve25519 conversion is unused, and no longer supported.

Available on crate feature cvt-x25519 only.

Convert an ed25519 private key to a curve25519 private key.

This creates a curve25519 key as described in section-5.1.5 of RFC8032: the bytes of the secret part of keypair are hashed using SHA-512, and the result is clamped (the first 3 bits of the first byte are cleared, the highest bit of the last byte is cleared, the second highest bit of the last byte is set).

Note: Using the same keypair for multiple purposes (such as key-exchange and signing) is considered bad practice. Don’t use this function unless you know what you’re doing. See On using the same key pair for Ed25519 and an X25519 based KEM.

This function is needed by the ArtiNativeKeystore from tor-keymgr to convert ed25519 private keys to x25519. This is because ArtiNativeKeystore stores x25519 private keys as ssh-ed25519 OpenSSH keys. Other similar use cases are also valid.

It’s important to note that converting a private key from ed25519 -> curve25519 -> ed25519 will yield an ExpandedKeypair that is not identical to the expanded version of the original Keypair: the lower halves (the keys) of the expanded key pairs will be the same, but their upper halves (the nonces) will be different.

Panics

If the debug_assertions feature is enabled, this function will double-check that the key it is about to return is clamped.

This panic should be impossible unless we have upgraded x25519-dalek without auditing this function.