How much file bloat does age-encryption give a file?

[Jediweirdo]

I'm trying to implement age file encryption through SOPS into a storage solution that uses QR Codes (weird, I know). As such, I would like to predict the size of any given file post-encryption accurately so I know what version of QR code I need to stuff the data into (assuming it can fit at all). So, does anyone know where I can find out how much extra bloat age encryption adds to a file?

[johanseb-te]

About a year late, but assuming a single X25519 stanza, and that my math is correct, it's 170 bytes for the header, and then the overhead for the actual encrypted data is 16 + (ceil(Size/64 KiB) * 12).

If you're encoding in QR codes, the max you'll ever fit in one is less than a single block, so you'll always have a 198 byte overhead.

[FiloSottile]

Almost! From the new age-inspect tool:

$ echo hello | age -r age1xmwwc06ly3ee5rytxm9mflaz2u56jjj36s0mypdrwsvlul66mv4q47ryef | age-inspect
<stdin> is an age file, version "age-encryption.org/v1".

This file is encrypted to the following recipient types:
  - "X25519"

This file does NOT use post-quantum encryption.

Size breakdown (assuming it decrypts successfully):

    Header                       168 bytes
    Encryption overhead           32 bytes
    Payload                        6 bytes
                        -------------------
    Total                        206 bytes

Tip: for machine-readable output, use --json.

[Jediweirdo]

Almost! From the new age-inspect tool:

    Total                        206 bytes

Interesting. A little late now, but it seems like I've been using the wrong size the entire time lol

[awnumar]

Should the description here be updated?

Currently it says:

age encrypted files are binary and not malleable, with around 200 bytes of overhead per recipient, plus 16 bytes every 64KiB of plaintext.

Whereas when using HybridRecipients, the ciphertext reports something like:

<stdin> is an age file, version "age-encryption.org/v1".

This file is encrypted to the following recipient types:
  - "mlkem768x25519"

This file uses post-quantum encryption.

Size breakdown (assuming it decrypts successfully):

    Header                      1627 bytes
    Encryption overhead           32 bytes
    Payload                       16 bytes
                        -------------------
    Total                       1675 bytes