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Merge pull request #326 from trail-of-forks/ap/wip-sct
Signed Certificate Timestamp verification
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,165 @@ | ||
| // Copyright 2023 The Sigstore Authors. | ||
| // | ||
| // Licensed under the Apache License, Version 2.0 (the "License"); | ||
| // you may not use this file except in compliance with the License. | ||
| // You may obtain a copy of the License at | ||
| // | ||
| // http://www.apache.org/licenses/LICENSE-2.0 | ||
| // | ||
| // Unless required by applicable law or agreed to in writing, software | ||
| // distributed under the License is distributed on an "AS IS" BASIS, | ||
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
| // See the License for the specific language governing permissions and | ||
| // limitations under the License. | ||
|
|
||
| use std::collections::HashMap; | ||
|
|
||
| use const_oid::db::rfc5912::{ID_EC_PUBLIC_KEY, RSA_ENCRYPTION, SECP_256_R_1}; | ||
| use digest::Digest; | ||
| use ring::{signature as ring_signature, signature::UnparsedPublicKey}; | ||
| use thiserror::Error; | ||
| use x509_cert::{ | ||
| der, | ||
| der::{Decode, Encode}, | ||
| spki::SubjectPublicKeyInfoOwned, | ||
| }; | ||
|
|
||
| #[derive(Error, Debug)] | ||
| pub enum KeyringError { | ||
| #[error("malformed key")] | ||
| KeyMalformed(#[from] x509_cert::der::Error), | ||
| #[error("unsupported algorithm")] | ||
| AlgoUnsupported, | ||
|
|
||
| #[error("requested key not in keyring")] | ||
| KeyNotFound, | ||
| #[error("verification failed")] | ||
| VerificationFailed, | ||
| } | ||
| type Result<T> = std::result::Result<T, KeyringError>; | ||
|
|
||
| /// A CT signing key. | ||
| struct Key { | ||
| inner: UnparsedPublicKey<Vec<u8>>, | ||
| /// The key's RFC 6962-style "key ID". | ||
| /// <https://datatracker.ietf.org/doc/html/rfc6962#section-3.2> | ||
| fingerprint: [u8; 32], | ||
| } | ||
|
|
||
| impl Key { | ||
| /// Creates a `Key` from a DER blob containing a SubjectPublicKeyInfo object. | ||
| pub fn new(spki_bytes: &[u8]) -> Result<Self> { | ||
| let spki = SubjectPublicKeyInfoOwned::from_der(spki_bytes)?; | ||
| let (algo, params) = if let Some(params) = &spki.algorithm.parameters { | ||
| // Special-case RSA keys, which don't have SPKI parameters. | ||
| if spki.algorithm.oid == RSA_ENCRYPTION && params == &der::Any::null() { | ||
| // TODO(tnytown): Do we need to support RSA keys? | ||
| return Err(KeyringError::AlgoUnsupported); | ||
| }; | ||
|
|
||
| (spki.algorithm.oid, params.decode_as()?) | ||
| } else { | ||
| return Err(KeyringError::AlgoUnsupported); | ||
| }; | ||
|
|
||
| match (algo, params) { | ||
| // TODO(tnytown): should we also accept ed25519, p384, ... ? | ||
| (ID_EC_PUBLIC_KEY, SECP_256_R_1) => Ok(Key { | ||
| inner: UnparsedPublicKey::new( | ||
| &ring_signature::ECDSA_P256_SHA256_ASN1, | ||
| spki.subject_public_key.raw_bytes().to_owned(), | ||
| ), | ||
| fingerprint: { | ||
| let mut hasher = sha2::Sha256::new(); | ||
| spki.encode(&mut hasher).expect("failed to hash key!"); | ||
| hasher.finalize().into() | ||
| }, | ||
| }), | ||
| _ => Err(KeyringError::AlgoUnsupported), | ||
| } | ||
| } | ||
| } | ||
|
|
||
| /// Represents a set of CT signing keys, each of which is potentially a valid signer for | ||
| /// Signed Certificate Timestamps (SCTs) or Signed Tree Heads (STHs). | ||
| pub struct Keyring(HashMap<[u8; 32], Key>); | ||
|
|
||
| impl Keyring { | ||
| /// Creates a `Keyring` from DER encoded SPKI-format public keys. | ||
| pub fn new<'a>(keys: impl IntoIterator<Item = &'a [u8]>) -> Result<Self> { | ||
| Ok(Self( | ||
| keys.into_iter() | ||
| .flat_map(Key::new) | ||
| .map(|k| Ok((k.fingerprint, k))) | ||
| .collect::<Result<_>>()?, | ||
| )) | ||
| } | ||
|
|
||
| /// Verifies `data` against a `signature` with a public key identified by `key_id`. | ||
| pub fn verify(&self, key_id: &[u8; 32], signature: &[u8], data: &[u8]) -> Result<()> { | ||
| let key = self.0.get(key_id).ok_or(KeyringError::KeyNotFound)?; | ||
|
|
||
| key.inner | ||
| .verify(data, signature) | ||
| .or(Err(KeyringError::VerificationFailed))?; | ||
|
|
||
| Ok(()) | ||
| } | ||
| } | ||
|
|
||
| #[cfg(test)] | ||
| mod tests { | ||
| use super::Keyring; | ||
| use crate::crypto::signing_key::ecdsa::{ECDSAKeys, EllipticCurve}; | ||
| use digest::Digest; | ||
| use std::io::Write; | ||
|
|
||
| #[test] | ||
| fn verify_keyring() { | ||
| let message = b"some message"; | ||
|
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||
| // Create a key pair and a keyring containing the public key. | ||
| let key_pair = ECDSAKeys::new(EllipticCurve::P256).unwrap(); | ||
| let signer = key_pair.to_sigstore_signer().unwrap(); | ||
| let pub_key = key_pair.as_inner().public_key_to_der().unwrap(); | ||
| let keyring = Keyring::new([pub_key.as_slice()]).unwrap(); | ||
|
|
||
| // Generate the signature. | ||
| let signature = signer.sign(message).unwrap(); | ||
|
|
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| // Generate the key id. | ||
| let mut hasher = sha2::Sha256::new(); | ||
| hasher.write(pub_key.as_slice()).unwrap(); | ||
| let key_id: [u8; 32] = hasher.finalize().into(); | ||
|
|
||
| // Check for success. | ||
| assert!(keyring | ||
| .verify(&key_id, signature.as_slice(), message) | ||
| .is_ok()); | ||
|
|
||
| // Check for failure with incorrect key id. | ||
| assert!(keyring | ||
| .verify(&[0; 32], signature.as_slice(), message) | ||
| .is_err()); | ||
|
|
||
| // Check for failure with incorrect payload. | ||
| let incorrect_message = b"another message"; | ||
|
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| assert!(keyring | ||
| .verify(&key_id, signature.as_slice(), incorrect_message) | ||
| .is_err()); | ||
|
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| // Check for failure with incorrect keyring. | ||
| let incorrect_key_pair = ECDSAKeys::new(EllipticCurve::P256).unwrap(); | ||
| let incorrect_keyring = Keyring::new([incorrect_key_pair | ||
| .as_inner() | ||
| .public_key_to_der() | ||
| .unwrap() | ||
| .as_slice()]) | ||
| .unwrap(); | ||
|
|
||
| assert!(incorrect_keyring | ||
| .verify(&key_id, signature.as_slice(), message) | ||
| .is_err()); | ||
| } | ||
| } |
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