Version 5.0.0

• Increased minimum PHP version to 8.0.
• Security: Asymmetric encryption now uses HKDF-BLAKE2b to extract a 256-bit uniformly random bit string for the encryption key, rather than using the raw X25519 output directly as an encryption key. This is important because Elliptic Curve Diffie-Hellman results in a random group element, but that isn't necessarily a uniformly random bit string.
  • Because Halite v4 and earlier did not perform this step, it's superficially susceptible to Cheon's attack. This reduces the effective security from 125 bits (Pollard's rho) to 123 bits, but neither is a practical concern today.
• Security: Halite v5 uses the PAE strategy from PASETO to prevent canonicalization attacks.
• Security: Halite v5 appends the random salt to HKDF's info parameter instead of the salt parameter. This allows us to meet the KDF Security Definition (which is stronger than a mere Pseudo-Random Function).
• Encryption now uses XChaCha20 instead of XSalsa20.
• The File class no longer supports the resource type. To migrate code, wrap your resource arguments in a ReadOnlyFile or MutableFile object.
• Added File::asymmetricEncrypt() and File::asymmetricDecrypt().

These security improvements were identified through an internal code review after years of studying new cryptographic attacks. Halite v4 ciphertexts are still decryptable with v5, so upgrading should be largely drop-in.