require "nacl"

# Generate a random secret key
key = NaCl::AEAD::XChaCha20Poly1305.keygen

# Initialize a XChaCha20Poly1305 cipher object
cipher = NaCl::AEAD::XChaCha20Poly1305.new(key)

# Generate a random nonce: a single-use value never repeated under the same key.
# The nonce isn't secret, and can be sent with the ciphertext.
# The cipher instance has a nonce_bytes method for determining how many bytes should be in a nonce.
nonce = NaCl::Random.random_bytes(cipher.nonce_bytes)

# Encrypt a message with XChaCha20Poly1305
message = "Crystal is amazing" # Message to be encrypted
ad = "" # Additional data sent *in the clear* to be authenticated. This can be `nil`.
ciphertext = cipher.encrypt_string(nonce, message, ad)
# => "..." string of random bytes, 16 bytes longer than the message.
# The extra 16 bytes are the authenticator.

# Decrypt a message, passing in the same additional data we used to encrypt.
decrypted_message = cipher.decrypt_string(nonce, ciphertext, ad)
# => "Crystal is amazing"

# But if the cipher has been tampered with:
cipher.decrypt_string(nonce, corrupted_ciphertext, ad)
# => NaCl::CryptoError

# For encrypting bytes you can use:
ciphertext = cipher.encrypt(nonce, message.bytes, ad)

# And to decrypt back to bytes
decrypted_bytes = cipher.decrypt(nonce, ciphertext, ad)
# => Bytes[...]

# Generate a new random signing key
signing_key = NaCl::SigningKey.generate

# Message to be signed
message = "Crystal is amazing

# Sign a message with the signing key
signature = signing_key.sign(message)

# Obtain the verify key for a given signing key
verify_key = signing_key.verify_key

# Convert the verify key to a string to send it to a third party
verify_key.to_s

# Create a VerifyKey object from a public key
verify_key = NaCl::VerifyKey.new(verify_key.bytes)

# Check the validity of a message's signature
# Will raise NaCl::BadSignatureError if the signature check fails
verify_key.verify(signature, message)