Mnemonic key recovery (#1579)

## Issue Addressed

N/A

## Proposed Changes

Add a  `lighthouse am wallet recover` command that recreates a wallet from a mnemonic but no validator keys.  Add a `lighthouse am validator recover` command which would directly create keys from a mnemonic for a given index and count.

## Additional Info


Co-authored-by: Paul Hauner <paul@paulhauner.com>

account_manager/src/common.rs

@@ -1,6 +1,15 @@
+use account_utils::PlainText;
+use account_utils::{read_mnemonic_from_user, strip_off_newlines};
 use clap::ArgMatches;
+use eth2_wallet::bip39::{Language, Mnemonic};
+use std::fs;
 use std::fs::create_dir_all;
 use std::path::{Path, PathBuf};
+use std::str::from_utf8;
+use std::thread::sleep;
+use std::time::Duration;
+
+pub const MNEMONIC_PROMPT: &str = "Enter the mnemonic phrase:";
 
 pub fn ensure_dir_exists<P: AsRef<Path>>(path: P) -> Result<(), String> {
     let path = path.as_ref();
@@ -19,3 +28,43 @@ pub fn base_wallet_dir(matches: &ArgMatches, arg: &'static str) -> Result<PathBu
         PathBuf::new().join(".lighthouse").join("wallets"),
     )
 }
+
+pub fn read_mnemonic_from_cli(
+    mnemonic_path: Option<PathBuf>,
+    stdin_password: bool,
+) -> Result<Mnemonic, String> {
+    let mnemonic = match mnemonic_path {
+        Some(path) => fs::read(&path)
+            .map_err(|e| format!("Unable to read {:?}: {:?}", path, e))
+            .and_then(|bytes| {
+                let bytes_no_newlines: PlainText = strip_off_newlines(bytes).into();
+                let phrase = from_utf8(&bytes_no_newlines.as_ref())
+                    .map_err(|e| format!("Unable to derive mnemonic: {:?}", e))?;
+                Mnemonic::from_phrase(phrase, Language::English).map_err(|e| {
+                    format!(
+                        "Unable to derive mnemonic from string {:?}: {:?}",
+                        phrase, e
+                    )
+                })
+            })?,
+        None => loop {
+            eprintln!("");
+            eprintln!("{}", MNEMONIC_PROMPT);
+
+            let mnemonic = read_mnemonic_from_user(stdin_password)?;
+
+            match Mnemonic::from_phrase(mnemonic.as_str(), Language::English) {
+                Ok(mnemonic_m) => {
+                    eprintln!("Valid mnemonic provided.");
+                    eprintln!("");
+                    sleep(Duration::from_secs(1));
+                    break mnemonic_m;
+                }
+                Err(_) => {
+                    eprintln!("Invalid mnemonic");
+                }
+            }
+        },
+    };
+    Ok(mnemonic)
+}

account_manager/src/validator/mod.rs

@@ -2,6 +2,7 @@ pub mod create;
 pub mod deposit;
 pub mod import;
 pub mod list;
+pub mod recover;
 
 use crate::common::base_wallet_dir;
 use clap::{App, Arg, ArgMatches};
@@ -24,6 +25,7 @@ pub fn cli_app<'a, 'b>() -> App<'a, 'b> {
         .subcommand(deposit::cli_app())
         .subcommand(import::cli_app())
         .subcommand(list::cli_app())
+        .subcommand(recover::cli_app())
 }
 
 pub fn cli_run<T: EthSpec>(matches: &ArgMatches, env: Environment<T>) -> Result<(), String> {
@@ -34,6 +36,7 @@ pub fn cli_run<T: EthSpec>(matches: &ArgMatches, env: Environment<T>) -> Result<
         (deposit::CMD, Some(matches)) => deposit::cli_run::<T>(matches, env),
         (import::CMD, Some(matches)) => import::cli_run(matches),
         (list::CMD, Some(matches)) => list::cli_run(matches),
+        (recover::CMD, Some(matches)) => recover::cli_run(matches),
         (unknown, _) => Err(format!(
             "{} does not have a {} command. See --help",
             CMD, unknown

account_manager/src/validator/recover.rs

@@ -0,0 +1,156 @@
+use super::create::STORE_WITHDRAW_FLAG;
+use super::import::STDIN_PASSWORD_FLAG;
+use crate::common::{ensure_dir_exists, read_mnemonic_from_cli};
+use crate::validator::create::COUNT_FLAG;
+use crate::{SECRETS_DIR_FLAG, VALIDATOR_DIR_FLAG};
+use account_utils::eth2_keystore::{keypair_from_secret, Keystore, KeystoreBuilder};
+use account_utils::random_password;
+use clap::{App, Arg, ArgMatches};
+use eth2_wallet::bip39::Seed;
+use eth2_wallet::{recover_validator_secret_from_mnemonic, KeyType, ValidatorKeystores};
+use std::path::PathBuf;
+use validator_dir::Builder as ValidatorDirBuilder;
+pub const CMD: &str = "recover";
+pub const FIRST_INDEX_FLAG: &str = "first-index";
+pub const MNEMONIC_FLAG: &str = "mnemonic-path";
+
+pub fn cli_app<'a, 'b>() -> App<'a, 'b> {
+    App::new(CMD)
+        .about(
+            "Recovers validator private keys given a BIP-39 mnemonic phrase. \
+            If you did not specify a `--first-index` or count `--count`, by default this will \
+            only recover the keys associated with the validator at index 0 for an HD wallet \
+            in accordance with the EIP-2333 spec.")
+        .arg(
+            Arg::with_name(FIRST_INDEX_FLAG)
+                .long(FIRST_INDEX_FLAG)
+                .value_name("FIRST_INDEX")
+                .help("The first of consecutive key indexes you wish to recover.")
+                .takes_value(true)
+                .required(false)
+                .default_value("0"),
+        )
+        .arg(
+            Arg::with_name(COUNT_FLAG)
+                .long(COUNT_FLAG)
+                .value_name("COUNT")
+                .help("The number of validator keys you wish to recover. Counted consecutively from the provided `--first_index`.")
+                .takes_value(true)
+                .required(false)
+                .default_value("1"),
+        )
+        .arg(
+            Arg::with_name(MNEMONIC_FLAG)
+                .long(MNEMONIC_FLAG)
+                .value_name("MNEMONIC_PATH")
+                .help(
+                    "If present, the mnemonic will be read in from this file.",
+                )
+                .takes_value(true)
+        )
+        .arg(
+            Arg::with_name(VALIDATOR_DIR_FLAG)
+                .long(VALIDATOR_DIR_FLAG)
+                .value_name("VALIDATOR_DIRECTORY")
+                .help(
+                    "The path where the validator directories will be created. \
+                    Defaults to ~/.lighthouse/validators",
+                )
+                .takes_value(true),
+        )
+        .arg(
+            Arg::with_name(SECRETS_DIR_FLAG)
+                .long(SECRETS_DIR_FLAG)
+                .value_name("SECRETS_DIR")
+                .help(
+                    "The path where the validator keystore passwords will be stored. \
+                    Defaults to ~/.lighthouse/secrets",
+                )
+                .takes_value(true),
+        )
+        .arg(
+            Arg::with_name(STORE_WITHDRAW_FLAG)
+                .long(STORE_WITHDRAW_FLAG)
+                .help(
+                    "If present, the withdrawal keystore will be stored alongside the voting \
+                    keypair. It is generally recommended to *not* store the withdrawal key and \
+                    instead generate them from the wallet seed when required.",
+                ),
+        )
+        .arg(
+            Arg::with_name(STDIN_PASSWORD_FLAG)
+                .long(STDIN_PASSWORD_FLAG)
+                .help("If present, read passwords from stdin instead of tty."),
+        )
+}
+
+pub fn cli_run(matches: &ArgMatches) -> Result<(), String> {
+    let validator_dir = clap_utils::parse_path_with_default_in_home_dir(
+        matches,
+        VALIDATOR_DIR_FLAG,
+        PathBuf::new().join(".lighthouse").join("validators"),
+    )?;
+    let secrets_dir = clap_utils::parse_path_with_default_in_home_dir(
+        matches,
+        SECRETS_DIR_FLAG,
+        PathBuf::new().join(".lighthouse").join("secrets"),
+    )?;
+    let first_index: u32 = clap_utils::parse_required(matches, FIRST_INDEX_FLAG)?;
+    let count: u32 = clap_utils::parse_required(matches, COUNT_FLAG)?;
+    let mnemonic_path: Option<PathBuf> = clap_utils::parse_optional(matches, MNEMONIC_FLAG)?;
+    let stdin_password = matches.is_present(STDIN_PASSWORD_FLAG);
+
+    ensure_dir_exists(&validator_dir)?;
+    ensure_dir_exists(&secrets_dir)?;
+
+    eprintln!("");
+    eprintln!("WARNING: KEY RECOVERY CAN LEAD TO DUPLICATING VALIDATORS KEYS, WHICH CAN LEAD TO SLASHING.");
+    eprintln!("");
+
+    let mnemonic = read_mnemonic_from_cli(mnemonic_path, stdin_password)?;
+
+    let seed = Seed::new(&mnemonic, "");
+
+    for index in first_index..first_index + count {
+        let voting_password = random_password();
+        let withdrawal_password = random_password();
+
+        let derive = |key_type: KeyType, password: &[u8]| -> Result<Keystore, String> {
+            let (secret, path) =
+                recover_validator_secret_from_mnemonic(seed.as_bytes(), index, key_type)
+                    .map_err(|e| format!("Unable to recover validator keys: {:?}", e))?;
+
+            let keypair = keypair_from_secret(secret.as_bytes())
+                .map_err(|e| format!("Unable build keystore: {:?}", e))?;
+
+            KeystoreBuilder::new(&keypair, password, format!("{}", path))
+                .map_err(|e| format!("Unable build keystore: {:?}", e))?
+                .build()
+                .map_err(|e| format!("Unable build keystore: {:?}", e))
+        };
+
+        let keystores = ValidatorKeystores {
+            voting: derive(KeyType::Voting, voting_password.as_bytes())?,
+            withdrawal: derive(KeyType::Withdrawal, withdrawal_password.as_bytes())?,
+        };
+
+        let voting_pubkey = keystores.voting.pubkey().to_string();
+
+        ValidatorDirBuilder::new(validator_dir.clone(), secrets_dir.clone())
+            .voting_keystore(keystores.voting, voting_password.as_bytes())
+            .withdrawal_keystore(keystores.withdrawal, withdrawal_password.as_bytes())
+            .store_withdrawal_keystore(matches.is_present(STORE_WITHDRAW_FLAG))
+            .build()
+            .map_err(|e| format!("Unable to build validator directory: {:?}", e))?;
+
+        println!(
+            "{}/{}\tIndex: {}\t0x{}",
+            index - first_index,
+            count - first_index,
+            index,
+            voting_pubkey
+        );
+    }
+
+    Ok(())
+}

account_manager/src/wallet/create.rs

@@ -5,7 +5,7 @@ use eth2_wallet::{
     bip39::{Language, Mnemonic, MnemonicType},
     PlainText,
 };
-use eth2_wallet_manager::{WalletManager, WalletType};
+use eth2_wallet_manager::{LockedWallet, WalletManager, WalletType};
 use std::ffi::OsStr;
 use std::fs::{self, File};
 use std::io::prelude::*;
@@ -70,46 +70,14 @@ pub fn cli_app<'a, 'b>() -> App<'a, 'b> {
 }
 
 pub fn cli_run(matches: &ArgMatches, base_dir: PathBuf) -> Result<(), String> {
-    let name: String = clap_utils::parse_required(matches, NAME_FLAG)?;
-    let wallet_password_path: PathBuf = clap_utils::parse_required(matches, PASSWORD_FLAG)?;
     let mnemonic_output_path: Option<PathBuf> = clap_utils::parse_optional(matches, MNEMONIC_FLAG)?;
-    let type_field: String = clap_utils::parse_required(matches, TYPE_FLAG)?;
-
-    let wallet_type = match type_field.as_ref() {
-        HD_TYPE => WalletType::Hd,
-        unknown => return Err(format!("--{} {} is not supported", TYPE_FLAG, unknown)),
-    };
-
-    let mgr = WalletManager::open(&base_dir)
-        .map_err(|e| format!("Unable to open --{}: {:?}", BASE_DIR_FLAG, e))?;
 
     // Create a new random mnemonic.
     //
     // The `tiny-bip39` crate uses `thread_rng()` for this entropy.
     let mnemonic = Mnemonic::new(MnemonicType::Words12, Language::English);
 
-    // Create a random password if the file does not exist.
-    if !wallet_password_path.exists() {
-        // To prevent users from accidentally supplying their password to the PASSWORD_FLAG and
-        // create a file with that name, we require that the password has a .pass suffix.
-        if wallet_password_path.extension() != Some(&OsStr::new("pass")) {
-            return Err(format!(
-                "Only creates a password file if that file ends in .pass: {:?}",
-                wallet_password_path
-            ));
-        }
-
-        create_with_600_perms(&wallet_password_path, random_password().as_bytes())
-            .map_err(|e| format!("Unable to write to {:?}: {:?}", wallet_password_path, e))?;
-    }
-
-    let wallet_password = fs::read(&wallet_password_path)
-        .map_err(|e| format!("Unable to read {:?}: {:?}", wallet_password_path, e))
-        .map(|bytes| PlainText::from(strip_off_newlines(bytes)))?;
-
-    let wallet = mgr
-        .create_wallet(name, wallet_type, &mnemonic, wallet_password.as_bytes())
-        .map_err(|e| format!("Unable to create wallet: {:?}", e))?;
+    let wallet = create_wallet_from_mnemonic(matches, &base_dir.as_path(), &mnemonic)?;
 
     if let Some(path) = mnemonic_output_path {
         create_with_600_perms(&path, mnemonic.phrase().as_bytes())
@@ -140,6 +108,48 @@ pub fn cli_run(matches: &ArgMatches, base_dir: PathBuf) -> Result<(), String> {
     Ok(())
 }
 
+pub fn create_wallet_from_mnemonic(
+    matches: &ArgMatches,
+    base_dir: &Path,
+    mnemonic: &Mnemonic,
+) -> Result<LockedWallet, String> {
+    let name: String = clap_utils::parse_required(matches, NAME_FLAG)?;
+    let wallet_password_path: PathBuf = clap_utils::parse_required(matches, PASSWORD_FLAG)?;
+    let type_field: String = clap_utils::parse_required(matches, TYPE_FLAG)?;
+
+    let wallet_type = match type_field.as_ref() {
+        HD_TYPE => WalletType::Hd,
+        unknown => return Err(format!("--{} {} is not supported", TYPE_FLAG, unknown)),
+    };
+
+    let mgr = WalletManager::open(&base_dir)
+        .map_err(|e| format!("Unable to open --{}: {:?}", BASE_DIR_FLAG, e))?;
+
+    // Create a random password if the file does not exist.
+    if !wallet_password_path.exists() {
+        // To prevent users from accidentally supplying their password to the PASSWORD_FLAG and
+        // create a file with that name, we require that the password has a .pass suffix.
+        if wallet_password_path.extension() != Some(&OsStr::new("pass")) {
+            return Err(format!(
+                "Only creates a password file if that file ends in .pass: {:?}",
+                wallet_password_path
+            ));
+        }
+
+        create_with_600_perms(&wallet_password_path, random_password().as_bytes())
+            .map_err(|e| format!("Unable to write to {:?}: {:?}", wallet_password_path, e))?;
+    }
+
+    let wallet_password = fs::read(&wallet_password_path)
+        .map_err(|e| format!("Unable to read {:?}: {:?}", wallet_password_path, e))
+        .map(|bytes| PlainText::from(strip_off_newlines(bytes)))?;
+
+    let wallet = mgr
+        .create_wallet(name, wallet_type, &mnemonic, wallet_password.as_bytes())
+        .map_err(|e| format!("Unable to create wallet: {:?}", e))?;
+    Ok(wallet)
+}
+
 /// Creates a file with `600 (-rw-------)` permissions.
 pub fn create_with_600_perms<P: AsRef<Path>>(path: P, bytes: &[u8]) -> Result<(), String> {
     let path = path.as_ref();

account_manager/src/wallet/mod.rs

@@ -1,5 +1,6 @@
 pub mod create;
 pub mod list;
+pub mod recover;
 
 use crate::{
     common::{base_wallet_dir, ensure_dir_exists},
@@ -21,6 +22,7 @@ pub fn cli_app<'a, 'b>() -> App<'a, 'b> {
         )
         .subcommand(create::cli_app())
         .subcommand(list::cli_app())
+        .subcommand(recover::cli_app())
 }
 
 pub fn cli_run(matches: &ArgMatches) -> Result<(), String> {
@@ -30,6 +32,7 @@ pub fn cli_run(matches: &ArgMatches) -> Result<(), String> {
     match matches.subcommand() {
         (create::CMD, Some(matches)) => create::cli_run(matches, base_dir),
         (list::CMD, Some(_)) => list::cli_run(base_dir),
+        (recover::CMD, Some(matches)) => recover::cli_run(matches, base_dir),
         (unknown, _) => Err(format!(
             "{} does not have a {} command. See --help",
             CMD, unknown

account_manager/src/wallet/recover.rs

@@ -0,0 +1,87 @@
+use crate::common::read_mnemonic_from_cli;
+use crate::wallet::create::create_wallet_from_mnemonic;
+use crate::wallet::create::{HD_TYPE, NAME_FLAG, PASSWORD_FLAG, TYPE_FLAG};
+use clap::{App, Arg, ArgMatches};
+use std::path::PathBuf;
+
+pub const CMD: &str = "recover";
+pub const MNEMONIC_FLAG: &str = "mnemonic-path";
+pub const STDIN_PASSWORD_FLAG: &str = "stdin-passwords";
+
+pub fn cli_app<'a, 'b>() -> App<'a, 'b> {
+    App::new(CMD)
+        .about("Recovers an EIP-2386 wallet from a given a BIP-39 mnemonic phrase.")
+        .arg(
+            Arg::with_name(NAME_FLAG)
+                .long(NAME_FLAG)
+                .value_name("WALLET_NAME")
+                .help(
+                    "The wallet will be created with this name. It is not allowed to \
+                            create two wallets with the same name for the same --base-dir.",
+                )
+                .takes_value(true)
+                .required(true),
+        )
+        .arg(
+            Arg::with_name(PASSWORD_FLAG)
+                .long(PASSWORD_FLAG)
+                .value_name("PASSWORD_FILE_PATH")
+                .help(
+                    "This will be the new password for your recovered wallet. \
+                    A path to a file containing the password which will unlock the wallet. \
+                    If the file does not exist, a random password will be generated and \
+                    saved at that path. To avoid confusion, if the file does not already \
+                    exist it must include a '.pass' suffix.",
+                )
+                .takes_value(true)
+                .required(true),
+        )
+        .arg(
+            Arg::with_name(MNEMONIC_FLAG)
+                .long(MNEMONIC_FLAG)
+                .value_name("MNEMONIC_PATH")
+                .help("If present, the mnemonic will be read in from this file.")
+                .takes_value(true),
+        )
+        .arg(
+            Arg::with_name(TYPE_FLAG)
+                .long(TYPE_FLAG)
+                .value_name("WALLET_TYPE")
+                .help(
+                    "The type of wallet to create. Only HD (hierarchical-deterministic) \
+                            wallets are supported presently..",
+                )
+                .takes_value(true)
+                .possible_values(&[HD_TYPE])
+                .default_value(HD_TYPE),
+        )
+        .arg(
+            Arg::with_name(STDIN_PASSWORD_FLAG)
+                .long(STDIN_PASSWORD_FLAG)
+                .help("If present, read passwords from stdin instead of tty."),
+        )
+}
+
+pub fn cli_run(matches: &ArgMatches, wallet_base_dir: PathBuf) -> Result<(), String> {
+    let mnemonic_path: Option<PathBuf> = clap_utils::parse_optional(matches, MNEMONIC_FLAG)?;
+    let stdin_password = matches.is_present(STDIN_PASSWORD_FLAG);
+
+    eprintln!("");
+    eprintln!("WARNING: KEY RECOVERY CAN LEAD TO DUPLICATING VALIDATORS KEYS, WHICH CAN LEAD TO SLASHING.");
+    eprintln!("");
+
+    let mnemonic = read_mnemonic_from_cli(mnemonic_path, stdin_password)?;
+
+    let wallet = create_wallet_from_mnemonic(matches, &wallet_base_dir.as_path(), &mnemonic)
+        .map_err(|e| format!("Unable to create wallet: {:?}", e))?;
+
+    println!("Your wallet has been successfully recovered.");
+    println!();
+    println!("Your wallet's UUID is:");
+    println!();
+    println!("\t{}", wallet.wallet().uuid());
+    println!();
+    println!("You do not need to backup your UUID or keep it secret.");
+
+    Ok(())
+}

book/src/SUMMARY.md

@@ -11,6 +11,7 @@
 * [Key Management](./key-management.md)
     * [Create a wallet](./wallet-create.md)
     * [Create a validator](./validator-create.md)
+    * [Key recovery](./key-recovery.md)
 * [Validator Management](./validator-management.md)
 	* [Importing from the Eth2 Launchpad](./validator-import-launchpad.md)
 * [Local Testnets](./local-testnets.md)

book/src/key-recovery.md

@@ -0,0 +1,65 @@
+# Key recovery
+
+
+Generally, validator keystore files are generated alongside a *mnemonic*. If
+the keystore and/or the keystore password are lost this mnemonic can
+regenerate a new, equivalent keystore with a new password.
+
+There are two ways to recover keys using the `lighthouse` CLI:
+
+- `lighthouse account validator recover`: recover one or more EIP-2335 keystores from a mnemonic.
+	These keys can be used directly in a validator client.
+- `lighthouse account wallet recover`: recover an EIP-2386 wallet from a
+	mnemonic.
+
+## ⚠️ Warning
+
+**Recovering validator keys from a mnemonic should only be used as a last
+resort.** Key recovery entails significant risks:
+
+- Exposing your mnemonic to a computer at any time puts it at risk of being
+	compromised. Your mnemonic is **not encrypted** and is a target for theft.
+- It's completely possible to regenerate a validator keypairs that is already active
+	on some other validator client. Running the same keypairs on two different
+	validator clients is very likely to result in slashing.
+
+## Recover EIP-2335 validator keystores
+
+A single mnemonic can generate a practically unlimited number of validator
+keystores using an *index*. Generally, the first time you generate a keystore
+you'll use index 0, the next time you'll use index 1, and so on. Using the same
+index on the same mnemonic always results in the same validator keypair being
+generated (see [EIP-2334](https://eips.ethereum.org/EIPS/eip-2334) for more
+detail).
+
+
+Using the `lighthouse account validator recover` command you can generate the
+keystores that correspond to one or more indices in the mnemonic:
+
+- `lighthouse account validator recover`: recover only index `0`.
+- `lighthouse account validator recover --count 2`: recover indices `0, 1`.
+- `lighthouse account validator recover --first-index 1`: recover only index `1`.
+- `lighthouse account validator recover --first-index 1 --count 2`: recover indices `1, 2`.
+
+
+For each of the indices recovered in the above commands, a directory will be
+created in the `--validator-dir` location (default `~/.lighthouse/validator`)
+which contains all the information necessary to run a validator using the
+`lighthouse vc` command. The password to this new keystore will be placed in
+the `--secrets-dir` (default `~/.lighthouse/secrets`).
+
+## Recover a EIP-2386 wallet
+
+Instead of creating EIP-2335 keystores directly, an EIP-2386 wallet can be
+generated from the mnemonic. This wallet can then be used to generate validator
+keystores, if desired. For example, the following command will create an
+encrypted wallet named `wally-recovered` from a mnemonic:
+
+```
+lighthouse account wallet recover --name wally-recovered
+```
+
+**⚠️ Warning:** the wallet will be created with a `nextaccount` value of `0`.
+This means that if you have already generated `n` validators, then the next `n`
+validators generated by this wallet will be duplicates. As mentioned
+previously, running duplicate validators is likely to result in slashing.

common/account_utils/src/lib.rs

@@ -107,6 +107,23 @@ pub fn read_password_from_user(use_stdin: bool) -> Result<ZeroizeString, String>
     result.map(ZeroizeString::from)
 }
 
+/// Reads a mnemonic phrase from TTY or stdin if `use_stdin == true`.
+pub fn read_mnemonic_from_user(use_stdin: bool) -> Result<String, String> {
+    let mut input = String::new();
+    if use_stdin {
+        io::stdin()
+            .read_line(&mut input)
+            .map_err(|e| format!("Error reading from stdin: {}", e))?;
+    } else {
+        let tty = File::open("/dev/tty").map_err(|e| format!("Error opening tty: {}", e))?;
+        let mut buf_reader = io::BufReader::new(tty);
+        buf_reader
+            .read_line(&mut input)
+            .map_err(|e| format!("Error reading from tty: {}", e))?;
+    }
+    Ok(input)
+}
+
 /// Provides a new-type wrapper around `String` that is zeroized on `Drop`.
 ///
 /// Useful for ensuring that password memory is zeroed-out on drop.

crypto/eth2_wallet/src/lib.rs

@@ -6,6 +6,6 @@ pub mod json_wallet;
 pub use bip39;
 pub use validator_path::{KeyType, ValidatorPath, COIN_TYPE, PURPOSE};
 pub use wallet::{
-    recover_validator_secret, DerivedKey, Error, KeystoreError, PlainText, Uuid,
-    ValidatorKeystores, Wallet, WalletBuilder,
+    recover_validator_secret, recover_validator_secret_from_mnemonic, DerivedKey, Error,
+    KeystoreError, PlainText, Uuid, ValidatorKeystores, Wallet, WalletBuilder,
 };

crypto/eth2_wallet/src/wallet.rs

@@ -285,3 +285,19 @@ pub fn recover_validator_secret(
 
     Ok((destination.secret().to_vec().into(), path))
 }
+
+/// Returns `(secret, path)` for the `key_type` for the validator at `index`.
+///
+/// This function should only be used for key recovery since it can easily lead to key duplication.
+pub fn recover_validator_secret_from_mnemonic(
+    secret: &[u8],
+    index: u32,
+    key_type: KeyType,
+) -> Result<(PlainText, ValidatorPath), Error> {
+    let path = ValidatorPath::new(index, key_type);
+    let master = DerivedKey::from_seed(secret).map_err(|()| Error::EmptyPassword)?;
+
+    let destination = path.iter_nodes().fold(master, |dk, i| dk.child(*i));
+
+    Ok((destination.secret().to_vec().into(), path))
+}