keyfork: add `bottoms-up` wizard

crates/derive/keyfork-derive-openpgp/src/main.rs

@@ -83,7 +83,7 @@ fn validate(
     let index = DerivationIndex::new(u32::from_be_bytes(pgp_u32), true)?;
 
     let path = DerivationPath::from_str(path)?;
-    assert_eq!(2, path.len(), "Expected path of m/{index}/account_id'");
+    assert!(path.len() >= 2, "Expected path of at least m/{index}/account_id'");
 
     let given_index = path.iter().next().expect("checked .len() above");
     assert_eq!(

crates/keyfork/src/cli/wizard.rs

@@ -1,6 +1,11 @@
 use super::Keyfork;
 use clap::{Parser, Subcommand};
-use std::{collections::HashSet, fs::File, io::IsTerminal, path::PathBuf};
+use std::{
+    collections::HashSet,
+    fs::File,
+    io::IsTerminal,
+    path::{Path, PathBuf},
+};
 
 use card_backend_pcsc::PcscBackend;
 use openpgp_card_sequoia::{state::Open, types::KeyType, Card};
@@ -185,6 +190,35 @@ fn generate_shard_secret(
     Ok(())
 }
 
+fn bottoms_up(key_discovery: &Path, threshold: u8, output: &Option<PathBuf>) -> Result<()> {
+    let seed = keyfork_entropy::generate_entropy_of_const_size::<{ 256 / 8 }>()?;
+    let stdout = std::io::stdout();
+    if output.is_none() {
+        assert!(
+            !stdout.is_terminal(),
+            "not printing shard to terminal, redirect output"
+        );
+    }
+
+    let opgp = OpenPGP::<DefaultTerminal>::new();
+    let certs = OpenPGP::<DefaultTerminal>::discover_certs(key_discovery)?;
+
+    if let Some(output_file) = output {
+        let output = File::create(output_file)?;
+        opgp.shard_and_encrypt(threshold, certs.len() as u8, &seed, &certs[..], output)?;
+    } else {
+        opgp.shard_and_encrypt(
+            threshold,
+            certs.len() as u8,
+            &seed,
+            &certs[..],
+            std::io::stdout(),
+        )?;
+    }
+
+    Ok(())
+}
+
 #[derive(Subcommand, Clone, Debug)]
 pub enum WizardSubcommands {
     /// Create a 256 bit secret and shard the secret to smart cards.
@@ -209,6 +243,24 @@ pub enum WizardSubcommands {
         #[arg(long)]
         output: Option<PathBuf>,
     },
+
+    /// Create a 256 bit secret and shard the secret to previously known OpenPGP certificates,
+    /// deriving the default OpenPGP certificate for the secret.
+    ///
+    /// This command was purpose-built for DEFCON and is not intended to be used normally, as it
+    /// implies keys used for sharding have been generated by a custom source.
+    BottomsUp {
+        /// The location of OpenPGP certificates to use when sharding.
+        key_discovery: PathBuf,
+
+        /// The minimum amount of keys required to decrypt the secret.
+        #[arg(long)]
+        threshold: u8,
+
+        /// The file to write the generated shard file to.
+        #[arg(long)]
+        output: Option<PathBuf>,
+    },
 }
 
 impl WizardSubcommands {
@@ -220,6 +272,11 @@ impl WizardSubcommands {
                 keys_per_shard,
                 output,
             } => generate_shard_secret(*threshold, *max, *keys_per_shard, output),
+            WizardSubcommands::BottomsUp {
+                key_discovery,
+                threshold,
+                output,
+            } => bottoms_up(key_discovery, *threshold, output),
         }
     }
 }