keyfork: impl `shard transport`

keyfork/src/cli/shard.rs

@@ -1,10 +1,12 @@
 use super::Keyfork;
 use clap::{builder::PossibleValue, Parser, Subcommand, ValueEnum};
 use std::{
-    io::{stdin, stdout, BufRead, BufReader, Read, Write},
+    io::{stdin, stdout, Read, Write},
     path::{Path, PathBuf},
 };
 
+const COULD_NOT_DETERMINE_FORMAT: &str = "could not determine format, try including --format";
+
 #[derive(Debug, Clone)]
 enum Format {
     OpenPGP(OpenPGP),
@@ -42,6 +44,14 @@ trait ShardExec {
     ) -> Result<(), Box<dyn std::error::Error>>
     where
         T: AsRef<Path>;
+
+    fn decrypt<T>(
+        &self,
+        key_discovery: Option<T>,
+        input: impl Read + Send + Sync,
+    ) -> Result<(), Box<dyn std::error::Error>>
+    where
+        T: AsRef<Path>;
 }
 
 #[derive(Clone, Debug)]
@@ -99,6 +109,32 @@ impl ShardExec for OpenPGP {
 
         Ok(())
     }
+
+    fn decrypt<T>(
+        &self,
+        key_discovery: Option<T>,
+        input: impl Read + Send + Sync,
+    ) -> Result<(), Box<dyn std::error::Error>>
+    where
+        T: AsRef<Path>,
+    {
+        let certs = key_discovery
+            .map(|kd| keyfork_shard::openpgp::discover_certs(kd.as_ref()))
+            .transpose()?
+            .unwrap_or(vec![]);
+
+        let mut encrypted_messages = keyfork_shard::openpgp::parse_messages(input)?;
+        let encrypted_metadata = encrypted_messages
+            .pop_front()
+            .expect("any pgp encrypted message");
+
+        keyfork_shard::openpgp::decrypt(
+            &certs,
+            &encrypted_metadata,
+            encrypted_messages.make_contiguous(),
+        )?;
+        Ok(())
+    }
 }
 
 #[derive(Clone, Debug)]
@@ -125,6 +161,13 @@ pub enum ShardSubcommands {
         key_discovery: PathBuf,
     },
 
+    /// Decrypt a single share and re-encrypt it to an ephemeral symmetric key using mnemonic-based
+    /// prompts. The mnemonics can be sent over insecure channels.
+    Transport {
+        /// The path to discover private keys from.
+        key_discovery: Option<PathBuf>,
+    },
+
     /// Combine multiple encrypted shares into a hex-encoded secret, printed to stdout.
     ///
     /// This command only accepts input from `keyfork shard split`, and is dependent on the format
@@ -143,8 +186,15 @@ impl ShardSubcommands {
         shard: &Shard,
         _keyfork: &Keyfork,
     ) -> Result<(), Box<dyn std::error::Error>> {
-        let stdin = stdin();
+        let mut stdin = stdin();
         let mut stdout = stdout();
+        let mut input = String::new();
+        stdin.read_to_string(&mut input)?;
+        let mut format = shard.format.clone();
+        // bang sandwich macro fun
+        if input.contains("BEGIN PGP MESSAGE") && !matches!(self, ShardSubcommands::Split { .. }) {
+            let _ = format.insert(Format::OpenPGP(OpenPGP));
+        }
         match self {
             ShardSubcommands::Split {
                 threshold,
@@ -152,30 +202,30 @@ impl ShardSubcommands {
                 key_discovery,
             } => {
                 assert!(threshold <= max, "threshold {threshold} <= max {max}");
-                let mut input = BufReader::new(stdin);
-                let mut hex_line = String::new();
-                input.read_line(&mut hex_line)?;
-                let secret = smex::decode(hex_line.trim())?;
-                match &shard.format {
+                let secret = smex::decode(input.trim())?;
+                match format {
                     Some(Format::OpenPGP(o)) => {
                         o.split(*threshold, *max, key_discovery, &secret, &mut stdout)
                     }
                     Some(Format::P256(_p)) => {
                         todo!()
                     }
-                    None => panic!("--format was not given"),
+                    None => panic!("{COULD_NOT_DETERMINE_FORMAT}"),
                 }
             }
-            ShardSubcommands::Combine {
-                key_discovery,
-            } => match &shard.format {
+            ShardSubcommands::Transport { key_discovery } => match format {
+                Some(Format::OpenPGP(o)) => o.decrypt(key_discovery.as_ref(), input.as_bytes()),
+                Some(Format::P256(_p)) => todo!(),
+                None => panic!("{COULD_NOT_DETERMINE_FORMAT}"),
+            },
+            ShardSubcommands::Combine { key_discovery } => match format {
                 Some(Format::OpenPGP(o)) => {
-                    o.combine(key_discovery.as_ref(), stdin, &mut stdout)
+                    o.combine(key_discovery.as_ref(), input.as_bytes(), &mut stdout)
                 }
                 Some(Format::P256(_p)) => {
                     todo!()
                 }
-                None => panic!("--format was not given"),
+                None => panic!("{COULD_NOT_DETERMINE_FORMAT}"),
             },
         }
     }