analogist / nacl-enigma

a fun cryptography demonstrator to give libsodium.js an Enigma / substitution-cipher-like UI

nacl-enigma

A fun cryptography demonstrator to give libsodium.js an Enigma / substitution-cipher-like UI

Design

Adapting a modern symmetric cipher to an "Engima"-like typewriter experience. This means:

• 1 plaintext character <-> 1 ciphertext character (for the most part)
• typable ciphertext on a keyboard
• "reversible" typing process (decryption to plaintext is the same typable process as "encrypting")

while keeping modern symmetric cipher primitives, provided by libsodium:

• modern key stretching of the passphrase
• modern cipher with authentication via AEAD construction

Implementation

1. a restricted typable charset of 32 characters [ !’,.a-z?] is chosen and all plaintext is interpreted as such a base32-encoded byte array
2. keys are derived from passphrase using Argon2id via libsodium.crypto_pwhash
3. the nonce is randomly generated and encoded via above base32 and described as a "preamble"
4. plaintext bytes are encrypted (currently with XSalsa20-Poly1305) via libsodium.secretbox
   1. (Plaintext is padded to mod8 characters with trailing spaces ( ) to retain readability while not introducing another padding character)
5. ciphertext bytes are encoded back to base32. The stream cipher construction with typable base32 ensures a character-by-character substitution cipher-like effect
6. the MAC is described as a "tamper-proof seal code" and can be used to authenticate