Standards and notions
The terms Obscura Vault uses, defined after the public standards they refer to.
| Term | Definition | In Obscura Vault |
|---|
| tar | Archive format that bundles files and folders into a single file; its interchange format (ustar) is described by the POSIX standard (IEEE Std 1003.1). | Container of an .obf archive |
| zstd (Zstandard) | Lossless compression algorithm, published as open source and described by RFC 8878. Lossless: once decompressed, each file is byte-for-byte identical to the original. | Compression of an .obf archive |
| AES-GCM | Authenticated encryption: the AES algorithm (FIPS 197) used in Galois/Counter Mode (NIST SP 800-38D). It makes the content unreadable without the key and detects any change to the encrypted content. | Optional encryption of an .obf archive |
| Ed25519 | EdDSA digital signature algorithm over the edwards25519 curve, described by RFC 8032. | Signature of every .obf archive |
| Digital signature | Value computed over data with a private key and verified with the matching public key: it shows that the data has not changed since it was signed. | Ed25519 signature of .obf archives |
| SHA-256 | Hash function of the SHA-2 family, standardized by NIST (FIPS 180-4), that sums up data as a 256-bit checksum. | Checksum of every file |
| Checksum | Result of a hash function applied to a file: the slightest change to the file gives a different checksum. Also called a hash or digest. | Computed with SHA-256, it serves as the reference for later checks |
| Fixity | The property of a file that has stayed identical to itself. The PREMIS data dictionary uses this name for the information used to verify whether an object has been altered in an undocumented or unauthorized way. | Checked by comparing the SHA-256 checksum with its reference; see Fixity checks |
App terms
| Term | Definition |
|---|
| .obf | Obscura Vault’s archive format, taken from Obscura Flow: a tar container compressed with zstd, encrypted with AES-GCM if you wish, and signed with Ed25519. See The .obf format. |
| Fixity check | Recomputing a file’s SHA-256 checksum and comparing it with its reference. A different checksum signals an alteration. |
| Scheduled audit | A fixity check run at regular intervals, without waiting for the day you need the file. |
| Verified good | The result for a file that was actually read again and whose checksum matches its reference. |
| Not verifiable | The result of a check that could not be completed, for example because the file is missing or unreadable. It never counts as “verified good”. |
| Preservation certificate | A document attesting the integrity of an .obf archive and the fixity of a file, as observed at a given date. See The preservation certificate. |