1 files changed, 247 insertions, 0 deletions

diff --git a/src/key_handling/encryption.rs b/src/key_handling/encryption.rs
new file mode 100644
index 0000000..0ef7f69
--- /dev/null
+++ b/src/key_handling/encryption.rs
@@ -0,0 +1,247 @@
+use anyhow::{anyhow, bail, ensure, Context, Result};
+use chacha20poly1305::{
+    aead::{rand_core::RngCore, Aead, AeadCore, KeyInit, OsRng, Payload},
+    XChaCha20Poly1305,
+};
+#[cfg(test)]
+use mockall::*;
+use nostr::{prelude::*, Keys};
+use rand::{distributions::Alphanumeric, thread_rng, Rng};
+use zeroize::Zeroize;
+
+#[derive(Default)]
+pub struct Encryptor;
+
+#[cfg_attr(test, automock)]
+pub trait EncryptDecrypt {
+    /// requires less CPU time if the password is long
+    fn encrypt_key(&self, keys: &Keys, password: &str) -> Result<String>;
+    fn decrypt_key(&self, encrypted_key: &str, password: &str) -> Result<Keys>;
+    /// generates a long random string
+    fn random_token(&self) -> String;
+}
+
+/// approach and code adapted from nostr gossip client
+impl EncryptDecrypt for Encryptor {
+    fn encrypt_key(&self, keys: &Keys, password: &str) -> Result<String> {
+        // Generate a random 16-byte salt
+        let salt = {
+            let mut salt: [u8; 16] = [0; 16];
+            OsRng.fill_bytes(&mut salt);
+            salt
+        };
+
+        let nonce = XChaCha20Poly1305::generate_nonce(&mut OsRng);
+
+        let log2_rounds: u8 = if password.len() > 20 {
+            // we have enough of entropy - no need to spend CPU time adding much more
+            1
+        } else {
+            // default (scrypt::Params::RECOMMENDED_LOG_N) is 17 but 30s is too long to wait
+            15
+        };
+
+        let associated_data: Vec<u8> = vec![1];
+
+        let ciphertext = {
+            let cipher = {
+                let symmetric_key = password_to_key(password, &salt, log2_rounds)
+                    .context("failed create encryption key from password")?;
+                XChaCha20Poly1305::new((&symmetric_key).into())
+            };
+            cipher
+                .encrypt(
+                    &nonce,
+                    Payload {
+                        msg: keys
+                            .secret_key()
+                            .context(
+                                "supplied key should reveal secret key. Is this a public key only?",
+                            )?
+                            .display_secret()
+                            .to_string()
+                            .as_bytes(),
+                        aad: &associated_data,
+                    },
+                )
+                .map_err(|_| anyhow!("ChaChaPoly1305 failed to encrypt nsec with password"))?
+        };
+        // Combine salt, IV and ciphertext
+        let mut concatenation: Vec<u8> = Vec::new();
+        concatenation.push(0x1); // 1 byte version number
+        concatenation.push(log2_rounds); // 1 byte for scrypt N (rounds)
+        concatenation.extend(salt); // 16 bytes of salt
+        concatenation.extend(nonce); // 24 bytes of nonce
+        concatenation.extend(associated_data); // 1 byte of key security
+        concatenation.extend(ciphertext); // 48 bytes of ciphertext expected
+        // Total length is 91 = 1 + 1 + 16 + 24 + 1 + 48
+
+        bech32::encode(
+            "ncryptsec",
+            concatenation.to_base32(),
+            bech32::Variant::Bech32,
+        )
+        .context("encrypted nsec failed to encode")
+    }
+
+    fn decrypt_key(&self, encrypted_key: &str, password: &str) -> Result<nostr::Keys> {
+        let data =
+            bech32::decode(encrypted_key).context("failed to decode encrypted key as bech32")?;
+        if data.0 != "ncryptsec" {
+            bail!("encrypted key is in the wrong format - it doesnt start with ncryptsec");
+        }
+        let concatenation = Vec::<u8>::from_base32(&data.1)
+            .context("failed to convert bech32::decode output to Vec<u8>")?;
+
+        // Break into parts
+        let version: u8 = concatenation[0];
+        ensure!(version == 0x1, "encryption version is incorrect");
+        let log2_rounds: u8 = concatenation[1];
+        let salt: [u8; 16] = concatenation[2..2 + 16].try_into()?;
+        let nonce = &concatenation[2 + 16..2 + 16 + 24];
+        let associated_data = &concatenation[(2 + 16 + 24)..=(2 + 16 + 24)];
+        let ciphertext = &concatenation[2 + 16 + 24 + 1..];
+
+        let cipher = {
+            let symmetric_key = password_to_key(password, &salt, log2_rounds)?;
+            XChaCha20Poly1305::new((&symmetric_key).into())
+        };
+
+        let payload = Payload {
+            msg: ciphertext,
+            aad: associated_data,
+        };
+
+        let mut inner_secret = cipher
+            .decrypt(nonce.into(), payload)
+            .map_err(|_| anyhow!("failed to decrypt"))?;
+
+        if associated_data.is_empty() {
+            bail!("invalid encrypted key");
+        }
+
+        let key = Keys::from_sk_str(
+            std::str::from_utf8(&inner_secret).context("inner secret is not [u8]")?,
+        )
+        .context("incorrect password. Key decrypted with password did not produce a valid nsec.")?;
+
+        inner_secret.zeroize();
+
+        Ok(key)
+    }
+
+    fn random_token(&self) -> String {
+        thread_rng()
+            .sample_iter(&Alphanumeric)
+            .take(32)
+            .map(char::from)
+            .collect()
+    }
+}
+
+/// uses scrypt to stretch password into key
+fn password_to_key(password: &str, salt: &[u8; 16], log_n: u8) -> Result<[u8; 32]> {
+    let params = scrypt::Params::new(log_n, 8, 1, 32)
+        .context("scrypt failed to generate params to stretch password")?;
+    let mut key: [u8; 32] = [0; 32];
+    if log_n > 14 {
+        println!("this may take a few seconds...");
+    }
+
+    scrypt::scrypt(password.as_bytes(), salt, &params, &mut key)
+        .context("scrypt failed to stretch password")?;
+    Ok(key)
+}
+
+#[cfg(test)]
+mod tests {
+    use test_utils::*;
+
+    use super::*;
+
+    #[test]
+    fn encrypt_key_produces_string_prefixed_with() -> Result<()> {
+        let s = Encryptor.encrypt_key(&nostr::Keys::generate(), TEST_PASSWORD)?;
+        assert!(s.starts_with("ncryptsec"));
+        Ok(())
+    }
+
+    #[test]
+    // ensures password encryption hasn't changed
+    fn decrypts_with_strong_password_from_reference_string() -> Result<()> {
+        let encryptor = Encryptor;
+        let decrypted_key = encryptor.decrypt_key(TEST_KEY_1_ENCRYPTED, TEST_PASSWORD)?;
+
+        assert_eq!(
+            format!(
+                "{}",
+                TEST_KEY_1_KEYS.secret_key().unwrap().to_bech32().unwrap()
+            ),
+            format!(
+                "{}",
+                decrypted_key.secret_key().unwrap().to_bech32().unwrap()
+            ),
+        );
+        Ok(())
+    }
+
+    #[test]
+    // ensures password encryption hasn't changed
+    fn decrypts_with_weak_password_from_reference_string() -> Result<()> {
+        let encryptor = Encryptor;
+        let decrypted_key = encryptor.decrypt_key(TEST_KEY_1_ENCRYPTED_WEAK, TEST_WEAK_PASSWORD)?;
+
+        assert_eq!(
+            format!(
+                "{}",
+                TEST_KEY_1_KEYS.secret_key().unwrap().to_bech32().unwrap()
+            ),
+            format!(
+                "{}",
+                decrypted_key.secret_key().unwrap().to_bech32().unwrap()
+            ),
+        );
+        Ok(())
+    }
+
+    #[test]
+    fn decrypts_key_encrypted_using_encrypt_key() -> Result<()> {
+        let encryptor = Encryptor;
+        let key = nostr::Keys::generate();
+        let s = encryptor.encrypt_key(&key, TEST_PASSWORD)?;
+        let newkey = encryptor.decrypt_key(s.as_str(), TEST_PASSWORD)?;
+
+        assert_eq!(
+            format!("{}", key.secret_key().unwrap().to_bech32().unwrap()),
+            format!("{}", newkey.secret_key().unwrap().to_bech32().unwrap()),
+        );
+        Ok(())
+    }
+
+    #[test]
+    fn decrypt_key_successfully_decrypts_key_encrypted_using_encrypt_key() -> Result<()> {
+        let encryptor = Encryptor;
+        let key = nostr::Keys::generate();
+        let s = encryptor.encrypt_key(&key, TEST_PASSWORD)?;
+        let newkey = encryptor.decrypt_key(s.as_str(), TEST_PASSWORD)?;
+
+        assert_eq!(
+            format!("{}", key.secret_key().unwrap().to_bech32().unwrap()),
+            format!("{}", newkey.secret_key().unwrap().to_bech32().unwrap()),
+        );
+        Ok(())
+    }
+
+    #[test]
+    fn password_to_key_returns_ok_with_standard_password() {
+        let salt = {
+            let mut salt: [u8; 16] = [0; 16];
+            OsRng.fill_bytes(&mut salt);
+            salt
+        };
+
+        let log2_rounds: u8 = 1;
+
+        assert!(password_to_key(TEST_PASSWORD, &salt, log2_rounds).is_ok());
+    }
+}