File / text encryption
Protected plaintext begins with one record-type byte.
| Type | Value |
|---|---|
| Metadata | 0x01 |
| Data | 0x02 |
| End | 0x03 |
Record 0 contains metadata. No bytes may follow the final record.
Technical specification
GCRYPT V1 and V2 .gcrypt formats.
Both formats use a 60-byte public header and the same cryptographic foundation. V2 adds Zstandard compression and folder support.
Public header
60 authenticated bytes.
The full header is included in the authenticated associated data for every record.
| Field | Size | V1 / V2 |
|---|---|---|
| Magic | 8 bytes | GCRYPT01 / GCRYPT02 |
| Version | 2 | 1 / 2 |
| KDF ID | 1 | 1 = Argon2id |
| AEAD ID | 1 | 1 = XChaCha20-Poly1305 |
| Argon m_cost | 4 | KiB |
| Argon t_cost | 4 | passes |
| Argon p_cost | 4 | parallelism |
| Chunk size | 4 | bytes |
| Salt | 16 | random |
| Nonce prefix | 16 | random |
Compression + folders
Encrypted metadata also includes source type, compression algorithm, and compression level. A folder is serialized into an internal TAR stream before compression.
- Zstandard compression.
- Zstandard checksum enabled.
- Symlinks rejected when creating V2.
- Links, devices, FIFOs, and special types rejected during extraction.
- Absolute paths and .. components rejected.
Key and nonce
key_256 = Argon2id(
password,
salt,
header_parameters
)
nonce[0..16] = nonce_prefix
nonce[16..24] = record_index u64 LEAAD
AAD =
header_60_bytes
||
record_index_u64_leThis cryptographically binds every record to its public parameters and its position.
Compatibility
No silent format changes.
ENCRYPT in V0.1.0 continues to produce V1, while COMPRESS + ENCRYPT continues to produce V2. A future reader must inspect Magic + Version before performing any key derivation.