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fcef_format.md

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fcef_format.md

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FCEF Format specification

Ver 1 (v0001) (DEPRECATED)

This document explains the specification of the FCEF file format Ver 1
DEPRECATED: due to the vulnerability in the Ver 1 encryption algorithm it's strongly recommended to use Ver 2

The FCEF format contain(s)

  1. nonce & Encrypted Data

These will be called tags hereafter

Encrypted data

A FCEF file generated with FileCrypt writes the nonce and encrypted data after 0x0. This tag contains the actual data that is used to decrypt.

Ver 2 (v0002)

This document explains the specification of the FCEF file format Ver 2

FCEF visual representation

The FCEF format contain(s)

  1. Version number
  2. Salt
  3. Nonce & Encrypted data

These will be called tags hereafter
The tag size(excluding Encrypted data) of FCEF Ver2 is 34 bytes

Version number

A FCEF file generated with FileCrypt writes the encryption version that it used to encrypt the file from 0x0 to 0x5. It's used to check whether the FCEF file can be decrypted using the current version of the software. Every version after Ver 1 will contain this tag.
Note: the last byte(0x5) of the version tag contains a line brake(\n)
Note: the version number ranges from v0001 to v9999

Salt

A FCEF file generated with FileCrypt writes the salt generated using rand.Read(salt) from 0x6 to 0x15 It's used while decrypting to regenerate the argon2 hash from the password.

Nonce & Encrypted data

A FCEF file generated with FileCrypt writes the nonce from 0x16-0x21 and encrypted data after 0x21.
This tag contains the actual data that is used to decrypt.