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format_spec.md

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PV2 File Format Specification

File Structure

[FILE_HEADER][IV_KEY][IV_HASH][PASSWORD_CHECK][ENCRYPTED_DATA][DATA_HASH][EOF_MARKER]

Section Details

1. FILE_HEADER (3 bytes)

  • Magic bytes: PV2
  • Identifies file format

2. IV_KEY (16 bytes)

  • AES initialization vector
  • Optional (may be stored in separate .ivkey file)

3. IV_HASH (32 bytes)

  • SHA-256 hash of IV_KEY
  • Used for integrity verification

4. PASSWORD_CHECK (8 bytes)

  • Encrypted known plaintext (EPV2FILE)
  • Used for password verification

5. ENCRYPTED_DATA (variable)

  • Data encrypted using AES-256 in EAX mode
  • Block size determined by available system RAM

6. DATA_HASH (32 bytes)

  • SHA-256 hash of encrypted data
  • Used for integrity verification

7. EOF_MARKER (3 bytes)

  • End-of-file marker: EOF

Companion Files

IV Key Files (.ivkey)

  • 16-byte IV when using separate storage
  • Named as [original]_N.ivkey

Recovery Key Files (.rkey)

  • SHA-256 hash of password in hex format
  • Named as [original]_N.rkey

Validation Process

  1. Verify FILE_HEADER
  2. Check IV_HASH matches computed IV
  3. Verify PASSWORD_CHECK decrypts correctly
  4. Validate DATA_HASH before decryption
  5. Confirm EOF_MARKER exists

Example Hex View

00000000: 50 56 32 00 01 23 45 67 89 AB CD EF 01 23 45 67  PV2..#Eg.....#Eg
00000010: 89 AB CD EF A1 B2 C3 D4 E5 F6 01 23 45 67 89 AB  ...........#Eg..
00000020: CD EF 01 23 45 67 89 AB CD EF 01 23 45 67 89 AB  ...#Eg.....#Eg..
00000030: CD EF 01 23 45 67 89 AB CD EF 01 23 45 67 89 AB  ...#Eg.....#Eg..
00000040: [Encrypted Data Block]                           [Binary]
0000XXXX: [SHA-256 Hash]                                   [Hash]
0000YYYY: EOF                                              EOF