Ed25519 sign
Sign a file with an Ed25519 private key, on your device.
Ed25519 sign unwraps a PKCS8 private key from its fixed PEM header, checks the prefix matches Ed25519 exactly, then signs the whole file and prints the signature as hex. A key wrapped for the wrong curve or key type is refused, naming what the tool expected instead. Nothing about the file name or a timestamp travels with the signature.
Questions
What key format does it need?
A PEM PRIVATE KEY block matching the fixed Ed25519 PKCS8 header from ed25519-keygen; a key for another curve or type is refused.
What does it sign?
The whole file as one message, not a hash you provide separately.
What format is the signature?
Hex text: the 64-byte signature written as 128 hexadecimal characters on one line, with no header or armor.
Does anything else travel with the signature?
No, no timestamp, file name or signer identity is bound into it.
Can I use this from the command line?
Yes, the same code runs on the page, the CLI and MCP.