feat: provide password feedback (#5111)

Description
---
Adds wallet password complexity feedback. Allows empty passwords. Adds a warning indicating that password changing functionality is [not yet implemented](#5003). Adds tests.

Closes [issue 5101](#5101).

Motivation and Context
---
The only check on a wallet password is that it not be empty. This introduces two issues:
- The user has no feedback on the practical strength of their password.
- The user may specifically wish not to set a password for fail-available backups.

This PR uses the [zxcvbn](https://crates.io/crates/zxcvbn) password complexity library to score a password and provide actionable feedback to the user. When the user enters a new password or changes their password, feedback is displayed if applicable. This is informational; the user is free to ignore the feedback if they wish.

Further, the user is now allowed to set an empty password, which may be desired for backups that must fail available. A warning is displayed if this happens.

Finally, a warning message is displayed during the password changing process to indicate that this functionality is incomplete.

How Has This Been Tested?
---
Existing CI passes. New tests pass. Tested manually for new wallets.

applications/tari_console_wallet/Cargo.toml

@@ -52,6 +52,7 @@ tracing = "0.1.26"
 unicode-segmentation = "1.6.0"
 unicode-width = "0.1"
 zeroize = "1"
+zxcvbn = "2"
 
 [dependencies.tari_core]
 path = "../../base_layer/core"

applications/tari_console_wallet/src/init/mod.rs

@@ -59,6 +59,7 @@ use tari_wallet::{
     WalletConfig,
     WalletSqlite,
 };
+use zxcvbn::zxcvbn;
 
 use crate::{
     cli::Cli,
@@ -77,6 +78,40 @@ pub enum WalletBoot {
     Recovery,
 }
 
+/// Get feedback, if available, for a weak passphrase
+fn get_password_feedback(passphrase: &SafePassword) -> Option<Vec<String>> {
+    std::str::from_utf8(passphrase.reveal())
+        .ok()
+        .and_then(|passphrase| zxcvbn(passphrase, &[]).ok())
+        .and_then(|scored| scored.feedback().to_owned())
+        .map(|feedback| feedback.suggestions().to_owned())
+        .map(|suggestion| suggestion.into_iter().map(|item| item.to_string()).collect())
+}
+
+// Display password feedback to the user
+fn display_password_feedback(passphrase: &SafePassword) {
+    if passphrase.reveal().is_empty() {
+        // The passphrase is empty, which the scoring library doesn't handle
+        println!("However, an empty password puts your wallet at risk against an attacker with access to this device.");
+        println!("Use this only if you are sure that your device is safe from prying eyes!");
+        println!();
+    } else if let Some(feedback) = get_password_feedback(passphrase) {
+        // The scoring library provided feedback
+        println!(
+            "However, the password you chose is weak; a determined attacker with access to your device may be able to \
+             guess it."
+        );
+        println!("You may want to consider changing it to a stronger one.");
+        println!("Here are some suggestions:");
+        for suggestion in feedback {
+            println!("- {}", suggestion);
+        }
+        println!();
+    } else {
+        // There is no feedback to provide
+    }
+}
+
 /// Gets the password provided by command line argument or environment variable if available.
 /// Otherwise prompts for the password to be typed in.
 pub fn get_or_prompt_password(
@@ -105,15 +140,7 @@ pub fn get_or_prompt_password(
 }
 
 fn prompt_password(prompt: &str) -> Result<SafePassword, ExitError> {
-    let password = loop {
-        let pass = prompt_password_stdout(prompt).map_err(|e| ExitError::new(ExitCode::IOError, e))?;
-        if pass.is_empty() {
-            println!("Password cannot be empty!");
-            continue;
-        } else {
-            break pass;
-        }
-    };
+    let password = prompt_password_stdout(prompt).map_err(|e| ExitError::new(ExitCode::IOError, e))?;
 
     Ok(SafePassword::from(password))
 }
@@ -144,7 +171,14 @@ pub async fn change_password(
     //     .await
     //     .map_err(|e| ExitError::new(ExitCode::WalletError, e))?;
 
-    println!("Wallet password changed successfully.");
+    println!("Passwords match.");
+
+    // If the passphrase is weak, let the user know
+    display_password_feedback(&passphrase);
+
+    // TODO: remove this warning when this functionality is added
+    println!();
+    println!("WARNING: Password change functionality is not yet completed, so continue to use your existing password!");
 
     Ok(())
 }
@@ -625,6 +659,11 @@ pub(crate) fn boot_with_password(
                 return Err(ExitError::new(ExitCode::InputError, "Passwords don't match!"));
             }
 
+            println!("Passwords match.");
+
+            // If the passphrase is weak, let the user know
+            display_password_feedback(&password);
+
             password
         },
         WalletBoot::Existing | WalletBoot::Recovery => {
@@ -635,3 +674,22 @@ pub(crate) fn boot_with_password(
 
     Ok((boot_mode, password))
 }
+
+#[cfg(test)]
+mod test {
+    use tari_utilities::SafePassword;
+
+    use super::get_password_feedback;
+
+    #[test]
+    fn weak_password() {
+        let weak_password = SafePassword::from("weak");
+        assert!(get_password_feedback(&weak_password).is_some());
+    }
+
+    #[test]
+    fn strong_password() {
+        let strong_password = SafePassword::from("This is a reasonably strong password!");
+        assert!(get_password_feedback(&strong_password).is_none());
+    }
+}