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Tool to sign files and verify signatures


Jsign tool is heavily inspired by minisign and asignify. It uses blake2b as the hash function and the highly secure Ed25519 public-key signature system. The keys are serialized in json.

Key features

  • Modern cryptography primitives (ed25519, curve25519, blake2b)
  • Protecting secret keys by passwords using pbkdf2-blake2b routine

Usage samples

Here are some (descriptive) usage examples of jsign utility:

  • Generate keypair:
$ jsign generate skey pkey
$ jsign generate --no-password skey pkey
  • Sign files
$ jsign sign skey file
  • Verify signature
$ jsign verify pkey file

Cryptographic basis

For digital signatures jsign uses ed25519 algorithm which is blazingly fast and proven to be secure even without random oracle (based on Schnorr scheme).

To sign a file, jsign does the following steps:

  1. Opens secret key file (decrypting it if needed)
  2. Calculates digest of a file
  3. Calculates ed25519 signature
  4. Write digest and signature to the output file in json format

To verify signature, jsign loads public key, verifies the signature in the same way, load file digest and verify corresponding file agains that digest.

Hence, jsign only sign digests of files and not files themselves, and a signature contains both digests and its ed25519 signature.

Keys storage

Secret key for jsign can be encrypted using password-based key derivation function, namely pbkdf2-blake2b. This function can be tuned for the number of rounds to increase amount of work required for an adversary to brute-force the encryption password into a valid encryption key.

jsign uses the json format for keys and signatures, doc.