svault-ai 0.9.8

//! YubiKey unlock via the FIDO2 hmac-secret extension.
//!
//! An enrolled YubiKey is an **independent keyslot** over the master key: a
//! stable 32-byte secret derived from the key (gated by a physical touch, and the
//! YubiKey PIN if one is set) wraps the master key in `.svault/master.yubikey.enc`,
//! exactly like the recovery code wraps it in `master.recovery.enc`. Either the
//! master passphrase **or** the YubiKey opens everything — this is a convenience
//! alternative slot, not a second factor.
//!
//! **Opt-in build feature.** The actual USB-HID/FIDO2 work (via `ctap-hid-fido2`)
//! is compiled only under the `yubikey` Cargo feature, because its `hidapi`
//! dependency needs `libudev` on Linux — which would otherwise break the default
//! build, `cargo install`, and docs.rs. Without the feature, the functions below
//! are stubs: [`is_present`] returns `false` (so the CLI/TUI never offer a key)
//! and [`enroll`] / [`derive_secret`] return a clear "not built with YubiKey
//! support" error. Build with `--features yubikey` (Linux also needs
//! `libudev-dev`) to get the real implementation.
#![allow(dead_code)]

use anyhow::Result;

/// True if at least one FIDO authenticator is currently connected (always `false`
/// when built without the `yubikey` feature).
pub fn is_present() -> bool {
    imp::is_present()
}

/// Enroll: create a FIDO2 credential carrying the hmac-secret extension. Returns
/// the credential id (non-secret) to store alongside the keyslot. Prompts a touch
/// (and uses `pin` if the key has one set). An empty/`None` pin uses no PIN/UV.
pub fn enroll(pin: Option<&str>) -> Result<Vec<u8>> {
    imp::enroll(pin)
}

/// Derive the stable 32-byte secret for `(credential_id, salt)`. The same inputs
/// always yield the same secret on the same physical key. Prompts a touch (+ PIN
/// if set). This is the KEK that wraps the master key in the YubiKey keyslot.
pub fn derive_secret(credential_id: &[u8], salt: &[u8; 32], pin: Option<&str>) -> Result<[u8; 32]> {
    imp::derive_secret(credential_id, salt, pin)
}

#[cfg(feature = "yubikey")]
mod imp {
    use anyhow::{anyhow, Result};
    use ctap_hid_fido2::fidokey::get_assertion::get_assertion_params::Extension as Gext;
    use ctap_hid_fido2::fidokey::make_credential::make_credential_params::Extension as Mext;
    use ctap_hid_fido2::fidokey::{GetAssertionArgsBuilder, MakeCredentialArgsBuilder};
    use ctap_hid_fido2::{Cfg, FidoKeyHid, FidoKeyHidFactory};

    /// Relying-party id stamped on Svault's FIDO2 credential.
    const RP_ID: &str = "svault.local";

    /// A fixed, non-secret challenge. We use the credential only for its stable
    /// hmac-secret output, never for attestation/assertion signature
    /// verification, so the challenge value is irrelevant — it just has to exist.
    const CHALLENGE: [u8; 32] = [0u8; 32];

    pub fn is_present() -> bool {
        !ctap_hid_fido2::get_fidokey_devices().is_empty()
    }

    /// Library config with all of ctap-hid-fido2's terminal chatter silenced. The
    /// crate otherwise prints "- Touch the sensor on the authenticator" (and debug
    /// lines) straight to stdout, which corrupts the raw-mode TUI. We render our
    /// own "touch now" prompt instead, so every callout here is muted.
    fn cfg() -> Cfg {
        let mut cfg = Cfg::init();
        cfg.enable_log = false;
        cfg.enable_keep_alive_msg = false;
        cfg.keep_alive_msg = String::new();
        cfg
    }

    fn open_device() -> Result<FidoKeyHid> {
        if !is_present() {
            return Err(anyhow!(
                "no YubiKey / FIDO2 device found — plug it in and try again"
            ));
        }
        FidoKeyHidFactory::create(&cfg())
            .map_err(|e| anyhow!("could not open the FIDO2 device: {e:?}"))
    }

    pub fn enroll(pin: Option<&str>) -> Result<Vec<u8>> {
        let device = open_device()?;
        let builder = MakeCredentialArgsBuilder::new(RP_ID, &CHALLENGE)
            .extensions(&[Mext::HmacSecret(Some(true))]);
        let builder = match pin {
            Some(p) if !p.is_empty() => builder.pin(p),
            _ => builder.without_pin_and_uv(),
        };
        let att = device
            .make_credential_with_args(&builder.build())
            .map_err(|e| anyhow!("YubiKey enrollment failed (is the hmac-secret extension supported, and the PIN correct?): {e:?}"))?;
        Ok(att.credential_descriptor.id)
    }

    pub fn derive_secret(
        credential_id: &[u8],
        salt: &[u8; 32],
        pin: Option<&str>,
    ) -> Result<[u8; 32]> {
        let device = open_device()?;
        let builder = GetAssertionArgsBuilder::new(RP_ID, &CHALLENGE)
            .credential_id(credential_id)
            .extensions(&[Gext::HmacSecret(Some(*salt))]);
        let builder = match pin {
            Some(p) if !p.is_empty() => builder.pin(p),
            _ => builder.without_pin_and_uv(),
        };
        let assertions = device
            .get_assertion_with_args(&builder.build())
            .map_err(|e| anyhow!("YubiKey unlock failed (wrong key or PIN?): {e:?}"))?;
        let assertion = assertions
            .first()
            .ok_or_else(|| anyhow!("YubiKey returned no assertion"))?;
        for ext in &assertion.extensions {
            if let Gext::HmacSecret(Some(out)) = ext {
                return Ok(*out);
            }
        }
        Err(anyhow!(
            "YubiKey did not return an hmac-secret value — the credential may lack the extension"
        ))
    }
}

#[cfg(not(feature = "yubikey"))]
mod imp {
    use anyhow::{anyhow, Result};

    fn unsupported<T>() -> Result<T> {
        Err(anyhow!(
            "this build has no YubiKey support — reinstall with `cargo install svault-ai --features yubikey` (Linux also needs libudev-dev)"
        ))
    }

    pub fn is_present() -> bool {
        false
    }

    pub fn enroll(_pin: Option<&str>) -> Result<Vec<u8>> {
        unsupported()
    }

    pub fn derive_secret(
        _credential_id: &[u8],
        _salt: &[u8; 32],
        _pin: Option<&str>,
    ) -> Result<[u8; 32]> {
        unsupported()
    }
}