fcry - [f]ile[cry]pt - initial commit (alpha 0.9.0)

A file en-/decryption tool for easy use.

Currently `fcry` uses `ChaCha20Poly1305` ([RFC 8439](https://datatracker.ietf.org/doc/html/rfc8439)) as [AEAD](https://en.wikipedia.org/wiki/Authenticated_encryption) cipher provided by the [chacha20poly1305](https://docs.rs/chacha20poly1305/latest/chacha20poly1305/) crate.

src/crypto.rs

@@ -0,0 +1,89 @@
+// SPDX-License-Identifier: GPL-3.0-only
+use chacha20poly1305::{
+    aead::{stream, NewAead},
+    ChaCha20Poly1305,
+};
+use rand::{rngs::OsRng, RngCore};
+
+use crate::error::*;
+use crate::utils::*;
+
+const BUFSIZE: usize = 64 * 1024; // 64 KiB
+
+fn new_random_nonce() -> Result<[u8; 7], FcryError> {
+    let mut nonce = [0u8; 7];
+    OsRng.try_fill_bytes(&mut nonce)?;
+    Ok(nonce)
+}
+
+pub fn encrypt<S: AsRef<str>>(
+    input_file: Option<S>,
+    output_file: Option<S>,
+    key: [u8; 32],
+) -> Result<(), FcryError> {
+    let mut f_plain = read_from_file_or_stdin(input_file);
+    let mut f_encrypted = write_to_file_or_stdout(output_file);
+
+    let nonce = new_random_nonce()?;
+    f_encrypted.write_all(&nonce)?;
+
+    let aead = ChaCha20Poly1305::new(&key.into());
+    let mut stream_encryptor = stream::EncryptorBE32::from_aead(aead, &nonce.into());
+
+    let mut buf = vec![0; BUFSIZE];
+    let mut read_bytes;
+
+    loop {
+        read_bytes = f_plain.read(&mut buf)?;
+
+        if read_bytes < BUFSIZE {
+            break;
+        }
+
+        stream_encryptor.encrypt_next_in_place(&[], &mut buf)?;
+        f_encrypted.write_all(&buf)?;
+        buf.truncate(BUFSIZE);
+    }
+
+    buf.truncate(read_bytes);
+    stream_encryptor.encrypt_last_in_place(&[], &mut buf)?;
+    f_encrypted.write_all(&buf)?;
+
+    Ok(())
+}
+
+pub fn decrypt<S: AsRef<str>>(
+    input_file: Option<S>,
+    output_file: Option<S>,
+    key: [u8; 32],
+) -> Result<(), FcryError> {
+    let mut f_encrypted = read_from_file_or_stdin(input_file);
+    let mut f_plain = write_to_file_or_stdout(output_file);
+
+    let mut nonce = [0u8; 7];
+    f_encrypted.read_exact(&mut nonce)?;
+
+    let aead = ChaCha20Poly1305::new(&key.into());
+    let mut stream_decryptor = stream::DecryptorBE32::from_aead(aead, &nonce.into());
+
+    let mut buf = vec![0; BUFSIZE + 16];
+    let mut read_bytes;
+
+    loop {
+        read_bytes = f_encrypted.read(&mut buf)?;
+
+        if read_bytes < BUFSIZE + 16 {
+            break;
+        }
+
+        stream_decryptor.decrypt_next_in_place(&[], &mut buf)?;
+        f_plain.write_all(&buf)?;
+        buf.resize(BUFSIZE + 16, 0);
+    }
+
+    buf.truncate(read_bytes);
+    stream_decryptor.decrypt_last_in_place(&[], &mut buf)?;
+    f_plain.write_all(&buf)?;
+
+    Ok(())
+}