diff options
Diffstat (limited to 'src/access')
| -rw-r--r-- | src/access/challenge.rs | 205 | ||||
| -rw-r--r-- | src/access/mod.rs | 1 |
2 files changed, 206 insertions, 0 deletions
diff --git a/src/access/challenge.rs b/src/access/challenge.rs new file mode 100644 index 0000000..64cafac --- /dev/null +++ b/src/access/challenge.rs @@ -0,0 +1,205 @@ +//! Logging in by key (`POST /auth/challenge`, `POST /auth/login/key`): a node hands out +//! a challenge, signed by it, naming it, valid for a while (`issue`); the user signs it +//! with one of its keys, as `ssh-keygen -Y sign -n continuum-login` does +//! (`access::sshsig`), and the node takes the signature once, from the user that key is +//! of in the registry (`registry::User::keys`; `take`). A challenge is checked by its +//! signature, so a node keeps none it handed out, only those used, until they expire +//! (`Used`). +//! +//! A challenge is `cc1.<payload>.<signature>` (each base64url, unpadded): the payload is +//! JSON naming the node, a random nonce and when it expires (Unix ms); the signature is +//! the node's, over `continuum/challenge/1\0` and the payload. + +use std::collections::HashMap; + +use base64::{Engine, engine::general_purpose::URL_SAFE_NO_PAD as B64URL}; +use serde::{Deserialize, Serialize}; + +use super::{registry, sshsig}; +use crate::document::ReadDoc; +use crate::identity::NodeKey; + +/// What a user's signature over a challenge is for (`sshsig`). +pub(crate) const NAMESPACE: &str = "continuum-login"; +/// What every challenge starts with. +const PREFIX: &str = "cc1"; +/// How long a challenge is valid (ms). +pub(crate) const LIFETIME_MS: u64 = 5 * 60 * 1000; +/// Used challenges kept at most: past it, logins by key wait for some to expire. +const MAX_USED: usize = 10_000; + +#[derive(Debug, Serialize, Deserialize)] +struct Payload { + node: String, + nonce: String, + exp: u64, +} + +fn message(payload: &[u8]) -> Vec<u8> { + let mut message = b"continuum/challenge/1\0".to_vec(); + message.extend_from_slice(payload); + message +} + +/// A new challenge by `key`'s node, valid from `now` for `LIFETIME_MS`; with when it +/// expires. +pub(crate) fn issue(key: &NodeKey, now: u64) -> (String, u64) { + let payload = Payload { + node: key.id(), + nonce: registry::new_id(), + exp: now.saturating_add(LIFETIME_MS), + }; + let bytes = serde_json::to_vec(&payload).expect("a challenge serializes"); + let signature = key.sign(&message(&bytes)); + ( + format!( + "{PREFIX}.{}.{}", + B64URL.encode(&bytes), + B64URL.encode(signature) + ), + payload.exp, + ) +} + +/// The challenges used, by nonce, with when each expires. +#[derive(Debug, Default)] +pub(crate) struct Used(HashMap<String, u64>); + +/// Takes `signature` (armored) over `challenge` as a login of `user`, whose registry +/// `doc` holds: a challenge of `key`'s node, unexpired at `now`, not used before (then +/// used, in `used`), signed by one of `user`'s keys, `user` enabled. Why not, if not. +pub(crate) fn take( + doc: &impl ReadDoc, + key: &NodeKey, + challenge: &str, + signature: &str, + user: &str, + now: u64, + used: &mut Used, +) -> Result<(), String> { + let mut parts = challenge.split('.'); + let (Some(PREFIX), Some(payload), Some(signed), None) = + (parts.next(), parts.next(), parts.next(), parts.next()) + else { + return Err("not a challenge (cc1.<payload>.<signature>)".to_owned()); + }; + let bytes = B64URL + .decode(payload) + .map_err(|_| "not a challenge: its payload doesn't decode".to_owned())?; + let by_node: [u8; 64] = B64URL + .decode(signed) + .ok() + .and_then(|signed| signed.try_into().ok()) + .ok_or("not a challenge: its signature doesn't decode")?; + if !crate::identity::verify(&key.public(), &message(&bytes), &by_node) { + return Err("not a challenge this node handed out".to_owned()); + } + let payload: Payload = serde_json::from_slice(&bytes) + .map_err(|_| "not a challenge: its payload isn't one".to_owned())?; + if payload.node != key.id() { + return Err("a challenge of another node".to_owned()); + } + if payload.exp <= now { + return Err("the challenge expired: ask for another".to_owned()); + } + used.0.retain(|_, exp| *exp > now); + if used.0.contains_key(&payload.nonce) { + return Err("the challenge was used: ask for another".to_owned()); + } + if used.0.len() >= MAX_USED { + return Err("too many logins by key at once: try again in a while".to_owned()); + } + let signer = sshsig::verify(signature, NAMESPACE, challenge.as_bytes())?; + let entry = registry::user(doc, user).ok_or_else(|| format!("no user {user}"))?; + if entry.disabled { + return Err(format!("{user} is disabled")); + } + if !entry.keys.values().any(|known| *known == signer) { + return Err(format!("{user} has no key {}", signer.fingerprint())); + } + used.0.insert(payload.nonce, payload.exp); + Ok(()) +} + +#[cfg(test)] +mod tests { + use super::*; + use crate::document::Document; + use crate::document::store; + use crate::document::testing::change; + use ed25519_dalek::SigningKey; + use serde_json::json; + + /// A registry with alice, holding `key`'s public key, and carol, disabled, holding + /// it too. + fn registry_with(key: &SigningKey) -> Document { + let line = sshsig::PublicKey(key.verifying_key().to_bytes()).line(); + let mut doc = Document::new(); + change(&mut doc, |doc| { + let mut alice = registry::entry("root", 1, &[]); + alice["keys"] = json!({ "laptop": line }); + store::write_path(doc, ®istry::user_path("alice"), &alice).unwrap(); + let mut carol = registry::entry("root", 1, &[]); + carol["keys"] = json!({ "laptop": line }); + carol["disabled"] = json!(true); + store::write_path(doc, ®istry::user_path("carol"), &carol).unwrap(); + store::write_path( + doc, + ®istry::user_path("bob"), + ®istry::entry("root", 1, &[]), + ) + .unwrap(); + }); + doc + } + + /// Signed by one of the user's keys, of this node, unexpired, once: taken; anything + /// else refused. + #[test] + fn what_a_login_by_key_takes() { + let node = NodeKey::from_seed([1; 32]); + let other_node = NodeKey::from_seed([2; 32]); + let key = SigningKey::from_bytes(&[5; 32]); + let stranger = SigningKey::from_bytes(&[6; 32]); + let doc = registry_with(&key); + let mut used = Used::default(); + let (challenge, exp) = issue(&node, 1000); + assert_eq!(exp, 1000 + LIFETIME_MS); + let signed = sshsig::sign(&key, NAMESPACE, challenge.as_bytes()); + // Another user, a disabled one, an unknown one, another key: refused. + assert!(take(&doc, &node, &challenge, &signed, "bob", 1001, &mut used).is_err()); + assert!(take(&doc, &node, &challenge, &signed, "carol", 1001, &mut used).is_err()); + assert!(take(&doc, &node, &challenge, &signed, "dave", 1001, &mut used).is_err()); + let foreign = sshsig::sign(&stranger, NAMESPACE, challenge.as_bytes()); + assert!(take(&doc, &node, &challenge, &foreign, "alice", 1001, &mut used).is_err()); + // For another purpose: refused. + let elsewhere = sshsig::sign(&key, "continuum-value", challenge.as_bytes()); + assert!( + take( + &doc, &node, &challenge, &elsewhere, "alice", 1001, &mut used + ) + .is_err() + ); + // Another node's, expired: refused. + assert!( + take( + &doc, + &other_node, + &challenge, + &signed, + "alice", + 1001, + &mut used + ) + .is_err() + ); + assert!(take(&doc, &node, &challenge, &signed, "alice", exp, &mut used).is_err()); + // Taken, once. + assert!(take(&doc, &node, &challenge, &signed, "alice", 1001, &mut used).is_ok()); + assert!(take(&doc, &node, &challenge, &signed, "alice", 1002, &mut used).is_err()); + // Tampered with. + let tampered = challenge.replacen("cc1.", "cc1.e30", 1); + let resigned = sshsig::sign(&key, NAMESPACE, tampered.as_bytes()); + assert!(take(&doc, &node, &tampered, &resigned, "alice", 1001, &mut used).is_err()); + } +} diff --git a/src/access/mod.rs b/src/access/mod.rs index bdb5124..73ae7c9 100644 --- a/src/access/mod.rs +++ b/src/access/mod.rs @@ -14,6 +14,7 @@ use serde::{Deserialize, Serialize}; use crate::document::meta; pub(crate) mod bans; +pub(crate) mod challenge; pub(crate) mod envelope; pub(crate) mod policy; pub(crate) mod registry; |