Move the scheme related primitives to dedicated modules

src/scheme/blake3.rs

@@ -0,0 +1,18 @@
+pub(crate) fn blake3_derive(context: &str, ikm: &[u8]) -> Vec<u8> {
+	blake3::derive_key(context, ikm).to_vec()
+}
+
+#[cfg(test)]
+mod tests {
+	#[test]
+	fn blake3_derive() {
+		assert_eq!(
+			super::blake3_derive("this is a context", b"7b47db8f365e5b602fd956d35985e9e1"),
+			vec![
+				0xc4, 0xf4, 0x6c, 0xf2, 0x03, 0xd9, 0x2d, 0x7b, 0x72, 0xe8, 0xe7, 0x90, 0xa3, 0x62,
+				0x2a, 0xf4, 0x3c, 0x2a, 0xab, 0x27, 0xc6, 0xb1, 0x8b, 0x46, 0x9d, 0x40, 0x61, 0x56,
+				0x19, 0x76, 0x88, 0xc4
+			]
+		);
+	}
+}

src/scheme/xchacha20poly1305.rs

@@ -0,0 +1,49 @@
+use crate::encryption::EncryptedData;
+use crate::error::Result;
+use chacha20poly1305::aead::{Aead, KeyInit, Payload};
+use chacha20poly1305::{Key, XChaCha20Poly1305, XNonce};
+
+pub(crate) fn xchacha20poly1305_encrypt(
+	key: &[u8],
+	data: &[u8],
+	aad: &str,
+) -> Result<EncryptedData> {
+	// Adapt the key
+	let key = Key::from_slice(key);
+
+	// Generate a nonce
+	let mut nonce: [u8; 24] = [0; 24];
+	getrandom::getrandom(&mut nonce)?;
+	let nonce = XNonce::from_slice(&nonce);
+
+	// Prepare the payload
+	let payload = Payload {
+		msg: data,
+		aad: aad.as_bytes(),
+	};
+
+	// Encrypt the payload
+	let cipher = XChaCha20Poly1305::new(key);
+	let ciphertext = cipher.encrypt(nonce, payload)?;
+
+	// Return the result
+	Ok(EncryptedData {
+		nonce: nonce.to_vec(),
+		ciphertext,
+	})
+}
+
+pub(crate) fn xchacha20poly1305_decrypt(
+	key: &[u8],
+	encrypted_data: &EncryptedData,
+	aad: &str,
+) -> Result<Vec<u8>> {
+	let key = Key::from_slice(key);
+	let nonce = XNonce::from_slice(&encrypted_data.nonce);
+	let payload = Payload {
+		msg: &encrypted_data.ciphertext,
+		aad: aad.as_bytes(),
+	};
+	let cipher = XChaCha20Poly1305::new(key);
+	Ok(cipher.decrypt(nonce, payload)?)
+}