A library to generate, verify and store Ed25519 keys and signatures. It uses the extended library (golang.org/x/crypto) for the underlying operations.

The generated keys and signatures are proper YAML files and human readable.

The signature file contains a hash of the public key - so that at verification time, the right private key may be used (in situations where there are lots of keys).

Signatures on large files are calculated efficiently by reading them in memory mapped mode (mmap(2)) and hashing the file contents using SHA-512. The Ed25519 signature is calculated on the file-hash.

A serialized Ed25519 public key looks like so:

pk: uxpDh+gqXojAmxA/6vxZHzA+Uk+8wogUwvEhPBlWgvo=

And, a serialized Ed25519 private key looks like so:

esk: t3vfqHbgUiA733KKPymFjWT8DdnBEkiMfsDHolPUdQWpvVn/F1Z4J6KYV3M5rGO9xgKxh5RAmqt+6LKgOiJAMQ==
salt: pPHKG55UJYtJ5wU0G9hBvNQJ0DvT0a7T4Fmj4aPB84s=
algo: scrypt-sha256
verify: JvjRjJMKhJhBmZngC3Pvq7x3KCLKt7gar1AAz7HB4qM=
Z: 131072
r: 16
p: 1

The Ed25519 private key is encrypted using Scrypt password hashing mechanism. Any user supplied passphrase to protect the private key is first pre-hashed using SHA-512 before being used in ```scrypt()``. In pseudo code, this operation looks like below:

passphrase = get_user_passphrase()
hpass      = SHA512(passphrase)
salt       = randombytes(32)
xorkey     = Scrypt(hpass, salt, N, r, p)
verify     = SHA256(salt, xorkey)
esk        = ed25519_private_key ^ xorkey

Where, N, r, p are Scrypt parameters. In our implementation:

N = 131072
r = 16
p = 1

verify is used during the decryption of the Ed25519 private key - before actually doing the "xor" operation. The code checks to ensure that the supplied passphrase yields the same value as verify.

A generated signature looks like below after serialization:

comment: inpfile=/tmp/file.txt
pkhash: 36z9tCwTIVNwwDlExrB0SQ==
signature: ow2oBP+buDbEvlNakOrsxgB5Yc/7PYyPVZCkfyu7oahw8BakF4Qf32uswPaKGZ8RVz4uXboYHdZtfrEjCgP/Cg==

Here, ```pkhash`` is a SHA256 of the public key needed to verify this signature.

GPL v2.0