1 files changed, 64 insertions, 0 deletions

diff --git a/packet-detector/src/validator.rs b/packet-detector/src/validator.rs
new file mode 100644
index 0000000..92e64d7
--- /dev/null
+++ b/packet-detector/src/validator.rs
@@ -0,0 +1,64 @@
+//! Certificate chain validation - signature only
+
+use anyhow::{anyhow, Result};
+use rustls::pki_types::CertificateDer;
+use x509_parser::prelude::*;
+
+pub struct ValidationResult {
+    pub valid: bool,
+    pub subject: String,
+    pub issuer: String,
+    pub error: Option<String>,
+}
+
+impl ValidationResult {
+    fn fail(subject: String, issuer: String, err: impl ToString) -> Self {
+        Self { valid: false, subject, issuer, error: Some(err.to_string()) }
+    }
+}
+
+pub struct CertValidator {
+    ca_der: Vec<u8>,
+}
+
+impl CertValidator {
+    pub fn with_ca_file(path: &str) -> Result<Self> {
+        let pem = std::fs::read_to_string(path)?;
+        let der = rustls_pemfile::certs(&mut pem.as_bytes())
+            .next()
+            .ok_or_else(|| anyhow!("No cert in PEM"))??;
+        Ok(Self { ca_der: der.to_vec() })
+    }
+
+    pub fn validate(&self, chain: &[Vec<u8>]) -> ValidationResult {
+        let Some(ee_der) = chain.first() else {
+            return ValidationResult::fail(String::new(), String::new(), "Empty chain");
+        };
+
+        let (subject, issuer) = match X509Certificate::from_der(ee_der) {
+            Ok((_, c)) => (c.subject().to_string(), c.issuer().to_string()),
+            Err(e) => return ValidationResult::fail(String::new(), String::new(), format!("{e:?}")),
+        };
+
+        let ca = CertificateDer::from(self.ca_der.clone());
+        let anchor = match webpki::anchor_from_trusted_cert(&ca) {
+            Ok(a) => a,
+            Err(e) => return ValidationResult::fail(subject, issuer, format!("CA: {e:?}")),
+        };
+
+        let cert = CertificateDer::from(ee_der.clone());
+        let ee = match webpki::EndEntityCert::try_from(&cert) {
+            Ok(c) => c,
+            Err(e) => return ValidationResult::fail(subject, issuer, format!("{e:?}")),
+        };
+
+        let intermediates: Vec<_> = chain[1..].iter().map(|c| CertificateDer::from(c.clone())).collect();
+        let algos = webpki::ALL_VERIFICATION_ALGS;
+        let time = webpki::types::UnixTime::since_unix_epoch(std::time::Duration::from_secs(4102444800)); // 2100
+
+        match ee.verify_for_usage(algos, &[anchor], &intermediates, time, webpki::KeyUsage::client_auth(), None, None) {
+            Ok(_) => ValidationResult { valid: true, subject, issuer, error: None },
+            Err(e) => ValidationResult::fail(subject, issuer, format!("{e:?}")),
+        }
+    }
+}