ed448ph

Ed448ph is the pre-hashed variant of the Ed448 digital signature scheme. It belongs to the Ed448 family defined in RFC 8032 and uses the same Edwards-curve (Ed448-Goldilocks) as Ed448, but signs the hash of a message rather than the raw message itself. The “ph” suffix stands for pre-hash, indicating that a cryptographic hash of the message is produced first and then passed to the signing algorithm with appropriate domain separation to distinguish it from the non-prehashed variant.

In Ed448ph, a private key yields a signing scalar and a corresponding public key on the Ed448 curve. To create a signature, the message is first hashed by a designated hash function to produce a digest, and this digest, together with the signer’s private material, is processed through the Ed448 signing procedure. Verification uses the public key and the digest to confirm the signature’s validity. The ph variant preserves the same high-level security properties and structure as Ed448, but its input to the signature algorithm is the pre-hashed digest rather than the original message.

Usage and interoperability: Ed448ph is intended for environments where the message may be large or streaming, or where pre-hashing is desirable for protocol design. It is standardized alongside Ed448 in RFC 8032 and is implemented in several modern cryptographic libraries that support the Ed448 family. As with other EdDSA variants, Ed448ph aims for deterministic signing and fast verification on supported platforms.

See also: Ed448, Ed25519, Ed25519ph.