Add support for AES128-GCM using HKDF-SHA256 to derive keys

src/scheme/aes.rs

@@ -0,0 +1,66 @@
+use crate::encrypted_data::EncryptedData;
+use crate::error::{Error, Result};
+use aes_gcm::aead::{Aead, KeyInit, Payload};
+use aes_gcm::{Aes128Gcm, Key, Nonce};
+
+// 96 bits (12 bytes)
+const NONCE_SIZE: usize = 12;
+
+pub(crate) fn aes128gcm_gen_nonce() -> Result<Vec<u8>> {
+	let mut nonce: [u8; NONCE_SIZE] = [0; NONCE_SIZE];
+	getrandom::getrandom(&mut nonce)?;
+	Ok(nonce.to_vec())
+}
+
+pub(crate) fn aes128gcm_encrypt(
+	key: &[u8],
+	nonce: &[u8],
+	data: &[u8],
+	aad: &str,
+) -> Result<EncryptedData> {
+	// Adapt the key and nonce
+	let key = Key::<Aes128Gcm>::from_slice(key);
+	let nonce = Nonce::from_slice(&nonce[0..NONCE_SIZE]);
+
+	// Prepare the payload
+	let payload = Payload {
+		msg: data,
+		aad: aad.as_bytes(),
+	};
+
+	// Encrypt the payload
+	let cipher = Aes128Gcm::new(key);
+	let ciphertext = cipher.encrypt(nonce, payload)?;
+
+	// Return the result
+	Ok(EncryptedData {
+		nonce: nonce.to_vec(),
+		ciphertext,
+	})
+}
+
+pub(crate) fn aes128gcm_decrypt(
+	key: &[u8],
+	encrypted_data: &EncryptedData,
+	aad: &str,
+) -> Result<Vec<u8>> {
+	// Adapt the key and nonce
+	let key = Key::<Aes128Gcm>::from_slice(key);
+	if encrypted_data.nonce.len() != NONCE_SIZE {
+		return Err(Error::InvalidNonceSize(
+			NONCE_SIZE,
+			encrypted_data.nonce.len(),
+		));
+	}
+	let nonce = Nonce::from_slice(&encrypted_data.nonce[0..NONCE_SIZE]);
+
+	// Prepare the payload
+	let payload = Payload {
+		msg: &encrypted_data.ciphertext,
+		aad: aad.as_bytes(),
+	};
+
+	// Decrypt the payload and return
+	let cipher = Aes128Gcm::new(key);
+	Ok(cipher.decrypt(nonce, payload)?)
+}

src/scheme/sha2.rs

@@ -0,0 +1,23 @@
+use hkdf::Hkdf;
+use sha2::Sha256;
+
+pub(crate) fn sha256_derive(context: &str, ikm: &[u8]) -> Vec<u8> {
+	let mut buff = [0u8; 16];
+	let hkdf = Hkdf::<Sha256>::new(None, ikm);
+	hkdf.expand(context.as_bytes(), &mut buff).unwrap();
+	buff.to_vec()
+}
+
+#[cfg(test)]
+mod tests {
+	#[test]
+	fn sha256_derive() {
+		assert_eq!(
+			super::sha256_derive("this is a context", b"7b47db8f365e5b602fd956d35985e9e1"),
+			vec![
+				0xad, 0xf2, 0xcd, 0x3a, 0x52, 0xfd, 0xf6, 0xad, 0x12, 0xce, 0xdd, 0x9a, 0x4d, 0x9e,
+				0xcd, 0x4b,
+			]
+		);
+	}
+}