Verify the quote certificate chain

untrusted/quote_verify/Cargo.toml

@@ -8,4 +8,7 @@ sha2 = "0.10.2"
 hex = "0.4.3"
 displaydoc = "0.2.3"
 p256 = { version = "0.11.1", features = [ "ecdsa", "pem" ] }
-x509-parser = "0.14.0"
+x509-parser = { version = "0.14.0", features = [ "verify" ] }
+
+[dev-dependencies]
+base64 = "0.13.0"

untrusted/quote_verify/data/DCAPCACert.pem

@@ -0,0 +1,16 @@
+-----BEGIN CERTIFICATE-----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+-----END CERTIFICATE-----

untrusted/quote_verify/src/lib.rs

@@ -13,6 +13,9 @@ use x509_parser::{
  pem::{self, Pem},
 };
 
+/// The root signing CA
+const ROOT_CERT_PEM: &[u8] = include_bytes!("../data/DCAPCACert.pem");
+
 // The size of a quote header. Table 3 of
 // https://download.01.org/intel-sgx/latest/dcap-latest/linux/docs/Intel_SGX_ECDSA_QuoteLibReference_DCAP_API.pdf
 const QUOTE_HEADER_SIZE: usize = 48;
@@ -85,6 +88,15 @@ const QUOTING_ENCLAVE_AUTHENTICATION_DATA_SIZE_START: usize =
 const QUOTING_ENCLAVE_AUTHENTICATION_DATA_START: usize =
  QUOTING_ENCLAVE_AUTHENTICATION_DATA_SIZE_START + 2;
 
+// TODO Should be looking up the certification data instead of hardcoding
+// offset, To be fixed with #25
+// The starting byte of the certification data for the quote.
+// *Certification Data* from Table 9 of
+// https://download.01.org/intel-sgx/latest/dcap-latest/linux/docs/Intel_SGX_ECDSA_QuoteLibReference_DCAP_API.pdf
+// which comes from the *QE Certification Data* of the Quote Signature Data
+// Structure in Table 4.
+const QUOTING_ENCLAVE_CERTIFICATION_DATA_START: usize = 0x41C;
+
 /// A quote for DCAP attestation
 pub struct Quote {
  bytes: Vec<u8>,
@@ -102,6 +114,32 @@ impl Quote {
  }
  }
 
+ pub fn verify_certificate_chain(&self) -> Result<(), Error> {
+ let (_, pem) = pem::parse_x509_pem(ROOT_CERT_PEM)?;
+ let root_cert = pem.parse_x509()?;
+
+ let pems =
+ Pem::iter_from_buffer(&self.bytes[QUOTING_ENCLAVE_CERTIFICATION_DATA_START..])
+ .collect::<Result<Vec<_>, _>>()?;
+
+ // Certs have a lifetime dependent on `pems` so must create them once
+ // the pems are held in place.
+ let mut certs = pems.iter().map(|p|{
+ p.parse_x509()
+ }).collect::<Result<Vec<_>, _>>()?;
+
+ // Certs are in order from leaf -> .. -> root. We need to start
+ // verifying from the root.
+ certs.reverse();
+
+ let mut key = root_cert.public_key();
+ for cert in certs.iter() {
+ cert.verify_signature(Some(&key))?;
+ key = cert.public_key();
+ }
+ Ok(())
+ }
+
  /// Verify the enclave report body within the quote.
  pub fn verify_enclave_report_body(&self) -> Result<(), Error> {
  let bytes = self.get_header_and_enclave_report_body();
@@ -175,9 +213,8 @@ impl Quote {
  /// the quoting enclave report.
  /// Note: The certificate is assumed to be valid.
  fn get_pck_pem(&self) -> Result<Pem, Error> {
- //TODO Should be looking up the certification data instead of hardcoding
- // offset, To be fixed with #25
- let (_, pem) = pem::parse_x509_pem(&self.bytes[0x41C..])?;
+ let (_, pem) =
+ pem::parse_x509_pem(&self.bytes[QUOTING_ENCLAVE_CERTIFICATION_DATA_START..])?;
  Ok(pem)
  }
 
@@ -210,8 +247,8 @@ impl Quote {
 #[derive(Display, Debug, PartialEq, Eq)]
 /// Error from verifying a Quote
 pub enum Error {
- /// Unable to load the signing Certificate
- Certificate,
+ /// Unable to validate certificate used in signing
+ Certificate(String),
 
  /// Failure to parse the Pem files from the quote data
  PemParsing(String),
@@ -238,6 +275,12 @@ impl From<spkiError> for Error {
  }
 }
 
+impl From<X509Error> for Error {
+ fn from(src: X509Error) -> Self {
+ Self::Certificate(src.to_string())
+ }
+}
+
 impl From<x509_parser::nom::Err<X509Error>> for Error {
  fn from(src: x509_parser::nom::Err<X509Error>) -> Self {
  Self::PemParsing(src.to_string())
@@ -250,11 +293,45 @@ impl From<x509_parser::nom::Err<PEMError>> for Error {
  }
 }
 
+impl From<PEMError> for Error {
+ fn from(src: PEMError) -> Self {
+ Self::PemParsing(src.to_string())
+ }
+}
+
 #[cfg(test)]
 mod tests {
  use super::*;
 
  const HW_QUOTE: &[u8] = include_bytes!("../tests/data/hw_quote.dat");
+
+ /// Returns the PEM Certificate of the `der` contents.
+ ///
+ /// #Arguments:
+ /// * `der` - The der version of a certificate to convert to PEM format
+ fn pem_certificate(der: &[u8]) -> String {
+ let encoded = base64::encode(der);
+ let pem_certificate = format!(
+ "-----BEGIN CERTIFICATE-----\n{}\n-----END CERTIFICATE-----\n",
+ encoded
+ );
+ pem_certificate
+ }
+
+ /// Returns the PEMs in `chain` as individual Strings per pem.
+ /// # Arguments:
+ /// * `chain` - Contiguous bytes representing a cert chain as PEMs.
+ fn extract_pems(chain: &[u8]) -> Vec<String> {
+ let pems = Pem::iter_from_buffer(chain)
+ .map(|p| {
+ let pem = p.unwrap();
+ pem_certificate(&pem.contents)
+ })
+ .collect::<Vec<_>>();
+
+ pems
+ }
+
  #[test]
  fn verify_valid_quote_report() {
  let quote = Quote::from_bytes(HW_QUOTE);
@@ -274,10 +351,7 @@ mod tests {
 
  #[test]
  fn failure_to_parse_pem_certificates() {
- // TODO Once more of the quote parsing logic comes in remove hard coded
- // value of 0x41c, based on current quote data file. To be fixed with
- // #25
- let quote = Quote::from_bytes(&HW_QUOTE[..0x41c]);
+ let quote = Quote::from_bytes(&HW_QUOTE[..QUOTING_ENCLAVE_CERTIFICATION_DATA_START]);
  assert!(matches!(
  quote.verify_quoting_enclave_report(),
  Err(Error::PemParsing(_))
@@ -356,4 +430,77 @@ mod tests {
  quote.bytes[QUOTING_ENCLAVE_REPORT_DATA_START + (ENCLAVE_REPORT_DATA_SIZE - 1)] = 1;
  assert_eq!(quote.verify_attestation_key(), Err(Error::AttestationKey));
  }
+
+ #[test]
+ fn verify_valid_certificate_chain() {
+ let quote = Quote::from_bytes(HW_QUOTE);
+ assert!(quote.verify_certificate_chain().is_ok());
+ }
+
+ #[test]
+ fn invalid_certificate_chain_fails() {
+ let mut hw_quote = HW_QUOTE.to_vec();
+ let pem_contents = hw_quote
+ .drain(QUOTING_ENCLAVE_CERTIFICATION_DATA_START..)
+ .collect::<Vec<_>>();
+ let pems = extract_pems(pem_contents.as_slice());
+
+ hw_quote.extend(pems[0].as_bytes());
+ // Skipping the intermediate cert to force a signing chain error
+ hw_quote.extend(pems[2].as_bytes());
+
+ let quote = Quote::from_bytes(hw_quote.as_slice());
+ assert!(matches!(
+ quote.verify_certificate_chain(),
+ Err(Error::Certificate(_))
+ ));
+ }
+
+ #[test]
+ fn bad_pem_file_in_cert_chain() {
+ let mut hw_quote = HW_QUOTE.to_vec();
+ let pem_contents = hw_quote
+ .drain(QUOTING_ENCLAVE_CERTIFICATION_DATA_START..)
+ .collect::<Vec<_>>();
+ let mut pems = extract_pems(pem_contents.as_slice());
+
+ // 'A' isn't significant, just a value inserted in the middle that
+ // should force an error state
+ let middle = pems[1].len() / 2;
+ pems[1].insert(middle, 'A');
+
+ hw_quote.extend(pems.join("").as_bytes());
+
+ let quote = Quote::from_bytes(hw_quote.as_slice());
+ assert!(matches!(
+ quote.verify_certificate_chain(),
+ Err(Error::PemParsing(_))
+ ));
+ }
+
+ #[test]
+ fn bad_der_representation_in_cert_chain() {
+ let mut hw_quote = HW_QUOTE.to_vec();
+
+ let pem_contents = hw_quote
+ .drain(QUOTING_ENCLAVE_CERTIFICATION_DATA_START..)
+ .collect::<Vec<_>>();
+ let mut pems = extract_pems(pem_contents.as_slice());
+
+ let (_, pem) = pem::parse_x509_pem(pems[2].as_bytes()).unwrap();
+ let mut der_contents = pem.contents.clone();
+
+ // '3' isn't significant, just a value inserted in the middle that
+ // should force an error state
+ der_contents.insert(der_contents.len() / 2, b'3');
+ pems[2] = pem_certificate(&der_contents);
+
+ hw_quote.extend(pems.join("").as_bytes());
+
+ let quote = Quote::from_bytes(hw_quote.as_slice());
+ assert!(matches!(
+ quote.verify_certificate_chain(),
+ Err(Error::PemParsing(_))
+ ));
+ }
 }