From 4e053b5efc3734b142f34028bcd5932bbf858105 Mon Sep 17 00:00:00 2001
From: Jack Grigg <thestr4d@gmail.com>
Date: Sat, 11 Feb 2023 22:04:14 +0000
Subject: [PATCH] TUI: Warn YubiKey 4 users of issue with PIN policy "Once"

---
 i18n/en-US/age_plugin_yubikey.ftl |  8 ++++
 src/main.rs                       | 71 +++++++++++++++++++++----------
 2 files changed, 56 insertions(+), 23 deletions(-)

diff --git a/i18n/en-US/age_plugin_yubikey.ftl b/i18n/en-US/age_plugin_yubikey.ftl
index 08d4f24..9a0bc66 100644
--- a/i18n/en-US/age_plugin_yubikey.ftl
+++ b/i18n/en-US/age_plugin_yubikey.ftl
@@ -76,6 +76,14 @@ cli-setup-name-identity       = 📛 Name this identity
 cli-setup-select-pin-policy   = 🔤 Select a PIN policy
 cli-setup-select-touch-policy = 👆 Select a touch policy
 
+cli-setup-yk4-pin-policy =
+    ⚠️ Your {-yubikey} is a {-yubikey} 4 series. With ephemeral applications like
+    {-age-plugin-yubikey}, a PIN policy of "Once" behaves like a PIN policy of
+    "Always", and your PIN will be requested for every decryption. However, you
+    might still benefit from a PIN policy of "Once" in long-running applications
+    like agents.
+cli-setup-yk4-pin-policy-confirm = Use PIN policy of "Once" with {-yubikey} 4?
+
 cli-setup-generate-new = Generate new identity in slot {$slot_index}?
 cli-setup-use-existing = Use existing identity in slot {$slot_index}?
 
diff --git a/src/main.rs b/src/main.rs
index f6cd93d..757cab6 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -487,29 +487,54 @@ fn main() -> Result<(), Error> {
                     .report(true)
                     .interact_text()?;
 
-                let pin_policy = match Select::new()
-                    .with_prompt(fl!("cli-setup-select-pin-policy"))
-                    .items(&[
-                        fl!("pin-policy-always"),
-                        fl!("pin-policy-once"),
-                        fl!("pin-policy-never"),
-                    ])
-                    .default(
-                        [PinPolicy::Always, PinPolicy::Once, PinPolicy::Never]
-                            .iter()
-                            .position(|p| {
-                                p == &flags.pin_policy.unwrap_or(builder::DEFAULT_PIN_POLICY)
-                            })
-                            .unwrap(),
-                    )
-                    .report(true)
-                    .interact_opt()?
-                {
-                    Some(0) => PinPolicy::Always,
-                    Some(1) => PinPolicy::Once,
-                    Some(2) => PinPolicy::Never,
-                    Some(_) => unreachable!(),
-                    None => return Ok(()),
+                let mut displayed_yk4_warning = false;
+                let pin_policy = loop {
+                    let pin_policy = match Select::new()
+                        .with_prompt(fl!("cli-setup-select-pin-policy"))
+                        .items(&[
+                            fl!("pin-policy-always"),
+                            fl!("pin-policy-once"),
+                            fl!("pin-policy-never"),
+                        ])
+                        .default(
+                            [PinPolicy::Always, PinPolicy::Once, PinPolicy::Never]
+                                .iter()
+                                .position(|p| {
+                                    p == &flags.pin_policy.unwrap_or(builder::DEFAULT_PIN_POLICY)
+                                })
+                                .unwrap(),
+                        )
+                        .report(true)
+                        .interact_opt()?
+                    {
+                        Some(0) => PinPolicy::Always,
+                        Some(1) => PinPolicy::Once,
+                        Some(2) => PinPolicy::Never,
+                        Some(_) => unreachable!(),
+                        None => return Ok(()),
+                    };
+
+                    // We can't preserve the PIN cache for YubiKey 4 series, because to
+                    // retrieve the serial we switch to the OTP applet.
+                    match (pin_policy, yubikey.version().major) {
+                        (PinPolicy::Once, 4) => {
+                            if !displayed_yk4_warning {
+                                eprintln!();
+                                eprintln!("{}", fl!("cli-setup-yk4-pin-policy"));
+                                eprintln!();
+                                displayed_yk4_warning = true;
+                            }
+
+                            if Confirm::new()
+                                .with_prompt(fl!("cli-setup-yk4-pin-policy-confirm"))
+                                .report(true)
+                                .interact()?
+                            {
+                                break pin_policy;
+                            }
+                        }
+                        _ => break pin_policy,
+                    }
                 };
 
                 let touch_policy = match Select::new()