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signify(1) file format

Signify is a minimalist file-signing utility using Ed25519 for tiny keys and signatures. Key files and signatures are plain text ASCII files.

File format

Key files and signatures use the same basic file format:

untrusted comment: <up to 1024 characters>\n
<base64>\n

The second line contains binary data in base64. Additional lines are not accepted unless it's a embedded signature.

Secret keys

Secret keys may be encrypted. Secret keys are bytes long and have the following structure:

  • Two bytes identifying the signature algorithm: "Ed" for Ed25519
  • Two bytes identifying the KDF algorithm: "BK" for bcrypt_pbkdf
  • Four bytes big-endian integer for the number of KDF rounds. If the number of rounds is zero, the secret key is not encrypted.
  • Sixteen byte salt for the KDF.
  • Eight byte checksum of the decrypted secret key itself. These are the first eight bytes of the SHA512 of the 64 byte secret Ed25519 key.
  • Eight byte random key identifier (keynum).
  • 64 bytes for the (encrypted) Ed25519 key itself.

Key encryption

keylen = 64
enckey = bcrypt_pbkdf(password, salt, kdfrounds, keylen)
decrypted_key = enckey ^ encrypted_key

Public key

Public keys follow this structure:

  • Two bytes identifying the signature algorithm: "Ed" for Ed25519
  • Eight byte random key identifier (keynum)
  • 32 byte Ed25519 public key

Signatures

  • Two bytes identifying the signature algorithm: "Ed" for Ed25519
  • Eight byte random key identifier (keynum)
  • 64 byte long Ed25519 signature

Embedded signatures

Embedded signatures are exactly the same as normal signatures, except that the contents of the message are directly concatenated to the signature:

untrusted comment: <comment>\n
<base64 signature>\n
message

References