Implement --generate command

Includes logic to help users manage their keys:

- If the key is using a default PIN, we require the user to change it.
- We set the PUK equal to the PIN so the user doesn't need to remember
  them separately.
- We migrate the default management key to a new PIN-protected key.

Cargo.lock

@@ -44,13 +44,18 @@ dependencies = [
  "age-core",
  "age-plugin",
  "bech32",
+ "chrono",
  "console",
+ "dialoguer",
  "elliptic-curve",
  "env_logger",
  "gumdrop",
+ "hex",
  "log",
  "p256",
+ "rand 0.8.3",
  "sha2",
+ "x509",
  "x509-parser",
  "yubikey-piv",
 ]
@@ -299,6 +304,18 @@ dependencies = [
  "opaque-debug",
 ]
 
+[[package]]
+name = "dialoguer"
+version = "0.8.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c9dd058f8b65922819fabb4a41e7d1964e56344042c26efbccd465202c23fa0c"
+dependencies = [
+ "console",
+ "lazy_static",
+ "tempfile",
+ "zeroize",
+]
+
 [[package]]
 name = "digest"
 version = "0.9.0"
@@ -443,6 +460,12 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "hex"
+version = "0.4.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7f24254aa9a54b5c858eaee2f5bccdb46aaf0e486a595ed5fd8f86ba55232a70"
+
 [[package]]
 name = "hkdf"
 version = "0.10.0"

Cargo.toml

@@ -14,13 +14,18 @@ edition = "2018"
 age-core = "0.5"
 age-plugin = "0.0"
 bech32 = "0.8"
+chrono = "0.4"
 console = "0.14"
+dialoguer = "0.8"
 elliptic-curve = "0.8"
 env_logger = "0.8"
 gumdrop = "0.8"
+hex = "0.4"
 log = "0.4"
 p256 = "0.7"
+rand = "0.8"
 sha2 = "0.9"
+x509 = "0.2"
 x509-parser = "0.9"
 yubikey-piv = { version = "0.3", features = ["untested"] }
 

src/builder.rs

@@ -0,0 +1,153 @@
+use rand::{rngs::OsRng, RngCore};
+use x509::RelativeDistinguishedName;
+use yubikey_piv::{
+    certificate::{Certificate, PublicKeyInfo},
+    key::{generate as yubikey_generate, AlgorithmId, RetiredSlotId, SlotId},
+    policy::{PinPolicy, TouchPolicy},
+    Key, YubiKey,
+};
+
+use crate::{
+    error::Error,
+    p256::Recipient,
+    util::POLICY_EXTENSION_OID,
+    yubikey::{self, Stub},
+    PLUGIN_NAME, USABLE_SLOTS,
+};
+
+const DEFAULT_PIN_POLICY: PinPolicy = PinPolicy::Once;
+const DEFAULT_TOUCH_POLICY: TouchPolicy = TouchPolicy::Always;
+
+pub(crate) struct IdentityBuilder {
+    slot: Option<RetiredSlotId>,
+    force: bool,
+    name: Option<String>,
+    pin_policy: Option<PinPolicy>,
+    touch_policy: Option<TouchPolicy>,
+}
+
+impl IdentityBuilder {
+    pub(crate) fn new(slot: Option<RetiredSlotId>) -> Self {
+        IdentityBuilder {
+            slot,
+            name: None,
+            pin_policy: None,
+            touch_policy: None,
+            force: false,
+        }
+    }
+
+    pub(crate) fn with_name(mut self, name: Option<String>) -> Self {
+        self.name = name;
+        self
+    }
+
+    pub(crate) fn with_pin_policy(mut self, pin_policy: Option<PinPolicy>) -> Self {
+        self.pin_policy = pin_policy;
+        self
+    }
+
+    pub(crate) fn with_touch_policy(mut self, touch_policy: Option<TouchPolicy>) -> Self {
+        self.touch_policy = touch_policy;
+        self
+    }
+
+    pub(crate) fn force(mut self, force: bool) -> Self {
+        self.force = force;
+        self
+    }
+
+    pub(crate) fn build(self, yubikey: &mut YubiKey) -> Result<(Stub, Recipient, String), Error> {
+        let slot = match self.slot {
+            Some(slot) => {
+                if !self.force {
+                    // Check that the slot is empty.
+                    if Key::list(yubikey)?
+                        .into_iter()
+                        .any(|key| key.slot() == SlotId::Retired(slot))
+                    {
+                        return Err(Error::SlotIsNotEmpty(slot));
+                    }
+                }
+
+                // Now either the slot is empty, or --force is specified.
+                slot
+            }
+            None => {
+                // Use the first empty slot.
+                let keys = Key::list(yubikey)?;
+                USABLE_SLOTS
+                    .iter()
+                    .find(|&&slot| {
+                        keys.iter()
+                            .find(|key| key.slot() == SlotId::Retired(slot))
+                            .is_none()
+                    })
+                    .cloned()
+                    .ok_or(Error::NoEmptySlots(yubikey.serial()))?
+            }
+        };
+
+        let pin_policy = self.pin_policy.unwrap_or(DEFAULT_PIN_POLICY);
+        let touch_policy = self.touch_policy.unwrap_or(DEFAULT_TOUCH_POLICY);
+
+        // No need to ask for users to enter their PIN if the PIN policy requires it,
+        // because here we _always_ require them to enter their PIN in order to access the
+        // protected management key (which is necessary in order to generate identities).
+        yubikey::manage(yubikey)?;
+
+        if let TouchPolicy::Never = touch_policy {
+            // No need to touch YubiKey
+        } else {
+            eprintln!("👆 Please touch the YubiKey");
+        }
+
+        // Generate a new key in the selected slot.
+        let generated = yubikey_generate(
+            yubikey,
+            SlotId::Retired(slot),
+            AlgorithmId::EccP256,
+            pin_policy,
+            touch_policy,
+        )?;
+
+        let recipient = match &generated {
+            PublicKeyInfo::EcP256(pubkey) => {
+                Recipient::from_pubkey(*pubkey).expect("YubiKey generates a valid pubkey")
+            }
+            _ => unreachable!(),
+        };
+        let stub = Stub::new(yubikey.serial(), slot, &recipient);
+
+        // Pick a random serial for the new self-signed certificate.
+        let mut serial = [0; 20];
+        OsRng.fill_bytes(&mut serial);
+
+        let name = self
+            .name
+            .unwrap_or(format!("age identity {}", hex::encode(stub.tag)));
+
+        Certificate::generate_self_signed(
+            yubikey,
+            SlotId::Retired(slot),
+            serial,
+            None,
+            &[
+                RelativeDistinguishedName::organization(PLUGIN_NAME),
+                RelativeDistinguishedName::organizational_unit(env!("CARGO_PKG_VERSION")),
+                RelativeDistinguishedName::common_name(&name),
+            ],
+            generated,
+            &[x509::Extension::regular(
+                POLICY_EXTENSION_OID,
+                &[pin_policy.into(), touch_policy.into()],
+            )],
+        )?;
+
+        Ok((
+            Stub::new(yubikey.serial(), slot, &recipient),
+            recipient,
+            chrono::Local::now().to_rfc3339_opts(chrono::SecondsFormat::Secs, true),
+        ))
+    }
+}

src/error.rs

@@ -5,14 +5,20 @@ use yubikey_piv::{key::RetiredSlotId, Serial};
 use crate::USABLE_SLOTS;
 
 pub enum Error {
+    CustomManagementKey,
+    InvalidPinLength,
+    InvalidPinPolicy(String),
     InvalidSlot(u8),
+    InvalidTouchPolicy(String),
     Io(io::Error),
     MultipleCommands,
     MultipleIdentities,
     MultipleYubiKeys,
+    NoEmptySlots(Serial),
     NoIdentities,
     NoMatchingSerial(Serial),
     SlotHasNoIdentity(RetiredSlotId),
+    SlotIsNotEmpty(RetiredSlotId),
     TimedOut,
     YubiKey(yubikey_piv::Error),
 }
@@ -34,11 +40,25 @@ impl From<yubikey_piv::error::Error> for Error {
 impl fmt::Debug for Error {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self {
+            Error::CustomManagementKey => {
+                writeln!(f, "Custom unprotected management keys are not supported.")?
+            }
+            Error::InvalidPinLength => writeln!(f, "The PIN needs to be 1-8 characters.")?,
+            Error::InvalidPinPolicy(s) => writeln!(
+                f,
+                "Invalid PIN policy '{}' (expected [always, once, never]).",
+                s
+            )?,
             Error::InvalidSlot(slot) => writeln!(
                 f,
                 "Invalid slot '{}' (expected number between 1 and 20).",
                 slot
             )?,
+            Error::InvalidTouchPolicy(s) => writeln!(
+                f,
+                "Invalid touch policy '{}' (expected [always, cached, never]).",
+                s
+            )?,
             Error::Io(e) => writeln!(f, "Failed to set up YubiKey: {}", e)?,
             Error::MultipleCommands => writeln!(
                 f,
@@ -52,6 +72,9 @@ impl fmt::Debug for Error {
                 f,
                 "Multiple YubiKeys are plugged in. Use --serial to select a single YubiKey."
             )?,
+            Error::NoEmptySlots(serial) => {
+                writeln!(f, "YubiKey with serial {} has no empty slots.", serial)?
+            }
             Error::NoIdentities => {
                 writeln!(f, "This YubiKey does not contain any age identities.")?
             }
@@ -63,6 +86,11 @@ impl fmt::Debug for Error {
                 "Slot {} does not contain an age identity or compatible key.",
                 USABLE_SLOTS.iter().position(|s| s == slot).unwrap() + 1
             )?,
+            Error::SlotIsNotEmpty(slot) => writeln!(
+                f,
+                "Slot {} is not empty. Use --force to overwrite the slot.",
+                USABLE_SLOTS.iter().position(|s| s == slot).unwrap() + 1
+            )?,
             Error::TimedOut => {
                 writeln!(f, "Timed out while waiting for a YubiKey to be inserted.")?
             }
@@ -70,6 +98,11 @@ impl fmt::Debug for Error {
                 yubikey_piv::error::Error::NotFound => {
                     writeln!(f, "Please insert the YubiKey you want to set up")?
                 }
+                yubikey_piv::error::Error::WrongPin { tries } => writeln!(
+                    f,
+                    "Invalid PIN ({} tries remaining before it is blocked)",
+                    tries
+                )?,
                 e => {
                     writeln!(f, "Error while communicating with YubiKey: {}", e)?;
                     use std::error::Error;

src/main.rs

@@ -7,6 +7,7 @@ use yubikey_piv::{
     Key, Readers,
 };
 
+mod builder;
 mod error;
 mod p256;
 mod plugin;
@@ -54,6 +55,9 @@ struct PluginOptions {
     )]
     age_plugin: Option<String>,
 
+    #[options(help = "Force --generate to overwrite a filled slot.")]
+    force: bool,
+
     #[options(help = "Generate a new YubiKey identity.")]
     generate: bool,
 
@@ -66,6 +70,15 @@ struct PluginOptions {
     #[options(help = "List all YubiKey keys that are compatible with age.", no_short)]
     list_all: bool,
 
+    #[options(
+        help = "Name for the generated identity. Defaults to 'age identity HEX_TAG'.",
+        no_short
+    )]
+    name: Option<String>,
+
+    #[options(help = "One of [always, once, never]. Defaults to 'once'.", no_short)]
+    pin_policy: Option<String>,
+
     #[options(
         help = "Specify which YubiKey to use, if more than one is plugged in.",
         no_short
@@ -77,6 +90,46 @@ struct PluginOptions {
         no_short
     )]
     slot: Option<u8>,
+
+    #[options(
+        help = "One of [always, cached, never]. Defaults to 'always'.",
+        no_short
+    )]
+    touch_policy: Option<String>,
+}
+
+fn generate(opts: PluginOptions) -> Result<(), Error> {
+    let serial = opts.serial.map(|s| s.into());
+    let slot = opts
+        .slot
+        .map(|slot| {
+            USABLE_SLOTS
+                .get(slot as usize - 1)
+                .cloned()
+                .ok_or(Error::InvalidSlot(slot))
+        })
+        .transpose()?;
+    let pin_policy = opts
+        .pin_policy
+        .map(util::pin_policy_from_string)
+        .transpose()?;
+    let touch_policy = opts
+        .touch_policy
+        .map(util::touch_policy_from_string)
+        .transpose()?;
+
+    let mut yubikey = yubikey::open(serial)?;
+
+    let (stub, recipient, created) = builder::IdentityBuilder::new(slot)
+        .with_name(opts.name)
+        .with_pin_policy(pin_policy)
+        .with_touch_policy(touch_policy)
+        .force(opts.force)
+        .build(&mut yubikey)?;
+
+    util::print_identity(stub, recipient, &created);
+
+    Ok(())
 }
 
 fn identity(opts: PluginOptions) -> Result<(), Error> {
@@ -232,7 +285,7 @@ fn main() -> Result<(), Error> {
         )?;
         Ok(())
     } else if opts.generate {
-        todo!()
+        generate(opts)
     } else if opts.identity {
         identity(opts)
     } else if opts.list {

src/util.rs

@@ -4,9 +4,27 @@ use yubikey_piv::{
     Key, YubiKey,
 };
 
-use crate::{p256::Recipient, yubikey::Stub, PLUGIN_NAME};
+use crate::{error::Error, p256::Recipient, yubikey::Stub, PLUGIN_NAME};
 
-const POLICY_EXTENSION_OID: &[u64] = &[1, 3, 6, 1, 4, 1, 41482, 3, 8];
+pub(crate) const POLICY_EXTENSION_OID: &[u64] = &[1, 3, 6, 1, 4, 1, 41482, 3, 8];
+
+pub(crate) fn pin_policy_from_string(s: String) -> Result<PinPolicy, Error> {
+    match s.as_str() {
+        "always" => Ok(PinPolicy::Always),
+        "once" => Ok(PinPolicy::Once),
+        "never" => Ok(PinPolicy::Never),
+        _ => Err(Error::InvalidPinPolicy(s)),
+    }
+}
+
+pub(crate) fn touch_policy_from_string(s: String) -> Result<TouchPolicy, Error> {
+    match s.as_str() {
+        "always" => Ok(TouchPolicy::Always),
+        "cached" => Ok(TouchPolicy::Cached),
+        "never" => Ok(TouchPolicy::Never),
+        _ => Err(Error::InvalidTouchPolicy(s)),
+    }
+}
 
 pub(crate) fn pin_policy_to_str(policy: Option<PinPolicy>) -> &'static str {
     match policy {

src/yubikey.rs

@@ -1,10 +1,11 @@
 //! Structs for handling YubiKeys.
 
 use bech32::{ToBase32, Variant};
+use dialoguer::Password;
 use std::fmt;
 use std::thread::sleep;
 use std::time::{Duration, SystemTime};
-use yubikey_piv::{key::RetiredSlotId, yubikey::Serial, Readers, YubiKey};
+use yubikey_piv::{key::RetiredSlotId, yubikey::Serial, MgmKey, Readers, YubiKey};
 
 use crate::{
     error::Error,
@@ -69,6 +70,57 @@ pub(crate) fn open(serial: Option<Serial>) -> Result<YubiKey, Error> {
     Ok(yubikey)
 }
 
+pub(crate) fn manage(yubikey: &mut YubiKey) -> Result<(), Error> {
+    eprintln!("");
+    let pin = Password::new()
+        .with_prompt(&format!(
+            "Enter PIN for YubiKey with serial {} (default is 123456)",
+            yubikey.serial(),
+        ))
+        .interact()?;
+    yubikey.verify_pin(pin.as_bytes())?;
+
+    // If the user is using the default PIN, help them to change it.
+    if pin == "123456" {
+        eprintln!("");
+        eprintln!("✨ Your key is using the default PIN. Let's change it!");
+        eprintln!("✨ We'll also set the PUK equal to the PIN.");
+        eprintln!("");
+        eprintln!("🔐 The PIN is up to 8 numbers, letters, or symbols. Not just numbers!");
+        eprintln!(
+            "❌ Your keys will be lost if the PIN and PUK are locked after 3 incorrect tries."
+        );
+        eprintln!("");
+        let current_puk = Password::new()
+            .with_prompt("Enter current PUK (default is 12345678)")
+            .interact()?;
+        let new_pin = Password::new()
+            .with_prompt("Choose a new PIN/PUK")
+            .with_confirmation("Repeat the PIN/PUK", "PINs don't match")
+            .interact()?;
+        if new_pin.len() > 8 {
+            return Err(Error::InvalidPinLength);
+        }
+        yubikey.change_puk(current_puk.as_bytes(), new_pin.as_bytes())?;
+        yubikey.change_pin(pin.as_bytes(), new_pin.as_bytes())?;
+    }
+
+    if let Ok(mgm_key) = MgmKey::get_protected(yubikey) {
+        yubikey.authenticate(mgm_key)?;
+    } else {
+        // Try to authenticate with the default management key.
+        yubikey
+            .authenticate(MgmKey::default())
+            .map_err(|_| Error::CustomManagementKey)?;
+
+        // Migrate to a PIN-protected management key.
+        let mgm_key = MgmKey::generate()?;
+        mgm_key.set_protected(yubikey)?;
+    }
+
+    Ok(())
+}
+
 /// A reference to an age key stored in a YubiKey.
 #[derive(Debug)]
 pub struct Stub {