louisswarren/saylouis

Send me encrypted messages

saylouis

Compilation

Use Argon2i key derivation to generate my public key from a passphrase. The public key is then hard-coded into the saylouis source before compilation.

Encryption

Generate a new X25519 key pair. Perform X25519 key exchange with my stored public key and hash the result to produce a shared secret. Use this shared secret and the public key for authenticated encryption via XChaCha20. Output a hidden form of the public key (indistinguishable from random noise), a MAC, and the ciphertext. Also output a fingerprint of the public key.

Details:

1. My public key lp is hard-coded into the binary.
2. Generate a 32-byte random seed seed.
3. Use crypto_hidden_key_pair(uhp, uk, seed) to get a (hidden) public key uhp and a private key uk.
4. Use crypto_x25519(rs, uk, lp) to get secret rs, and then hash it using ss = BLAKE2b(rs || uhp || lp) to get the final shared secret.
5. Output uhp.
6. Input at most blocksize bytes.
7. Call crypto_lock on ss, plaintext, using a count (starting at zero) of the blocks as the nonce, to get the ciphertext and mac.
8. Output mac || ciphertext. If there's more input to handle, go to 6.
9. Display a fingerprint of uhp.

Decryption

Read the public key from the input, display the fingerprint and confirm it's okay to continue. Use Argon2i key derivation to compute my public and private key from a passphrase. Authenticate the ciphertext using the mac, decrypt using the nonce and my secret key.