persist: avoid passing secrets in as Vec<u8>

This avoids having them as 'loose' unzeroized type on the way to being moved
to their final home.

This is sufficient, because:

- tls12: the secret comes from
  `tls12::ConnectionSecrets::master_secret()` which borrows from its
  internal storage; `tls12::ConnectionSecrets::drop` zeroes this
  storage.
- tls13: the secret comes from
  `resumption_master_secret_and_derive_ticket_psk`, of type `hkdf::OkmBlock`,
  which we borrow from.  Only once the borrow finishes will that be
  zeroized.

rustls/src/client/handy.rs

@@ -245,7 +245,7 @@ mod tests {
                     tls12_suite,
                     SessionId::empty(),
                     Vec::new(),
-                    Vec::new(),
+                    &[],
                     Vec::new(),
                     now,
                     0,
@@ -264,16 +264,7 @@ mod tests {
         };
         c.insert_tls13_ticket(
             &name,
-            Tls13ClientSessionValue::new(
-                tls13_suite,
-                Vec::new(),
-                Vec::new(),
-                Vec::new(),
-                now,
-                0,
-                0,
-                0,
-            ),
+            Tls13ClientSessionValue::new(tls13_suite, Vec::new(), &[], Vec::new(), now, 0, 0, 0),
         );
         assert!(c.take_tls13_ticket(&name).is_none());
     }

rustls/src/client/tls12.rs

@@ -978,7 +978,7 @@ impl ExpectFinished {
             self.secrets.suite(),
             self.session_id,
             ticket,
-            self.secrets.get_master_secret(),
+            self.secrets.master_secret(),
             cx.common
                 .peer_certificates
                 .clone()

rustls/src/client/tls13.rs

@@ -958,7 +958,7 @@ impl ExpectTraffic {
         let mut value = persist::Tls13ClientSessionValue::new(
             self.suite,
             nst.ticket.0.clone(),
-            secret.as_ref().to_vec(),
+            secret.as_ref(),
             cx.common
                 .peer_certificates
                 .clone()

rustls/src/msgs/persist.rs

@@ -83,7 +83,7 @@ impl Tls13ClientSessionValue {
     pub(crate) fn new(
         suite: &'static Tls13CipherSuite,
         ticket: Vec<u8>,
-        secret: Vec<u8>,
+        secret: &[u8],
         server_cert_chain: Vec<CertificateDer<'static>>,
         time_now: UnixTime,
         lifetime_secs: u32,
@@ -158,7 +158,7 @@ impl Tls12ClientSessionValue {
         suite: &'static Tls12CipherSuite,
         session_id: SessionId,
         ticket: Vec<u8>,
-        master_secret: Vec<u8>,
+        master_secret: &[u8],
         server_cert_chain: Vec<CertificateDer<'static>>,
         time_now: UnixTime,
         lifetime_secs: u32,
@@ -218,14 +218,14 @@ pub struct ClientSessionCommon {
 impl ClientSessionCommon {
     fn new(
         ticket: Vec<u8>,
-        secret: Vec<u8>,
+        secret: &[u8],
         time_now: UnixTime,
         lifetime_secs: u32,
         server_cert_chain: Vec<CertificateDer<'static>>,
     ) -> Self {
         Self {
             ticket: PayloadU16(ticket),
-            secret: Zeroizing::new(PayloadU8(secret)),
+            secret: Zeroizing::new(PayloadU8(secret.to_vec())),
             epoch: time_now.as_secs(),
             lifetime_secs: cmp::min(lifetime_secs, MAX_TICKET_LIFETIME),
             server_cert_chain,
@@ -355,7 +355,7 @@ impl ServerSessionValue {
         sni: Option<&DnsName>,
         v: ProtocolVersion,
         cs: CipherSuite,
-        ms: Vec<u8>,
+        ms: &[u8],
         client_cert_chain: Option<CertificatePayload>,
         alpn: Option<Vec<u8>>,
         application_data: Vec<u8>,
@@ -366,7 +366,7 @@ impl ServerSessionValue {
             sni: sni.cloned(),
             version: v,
             cipher_suite: cs,
-            master_secret: Zeroizing::new(PayloadU8::new(ms)),
+            master_secret: Zeroizing::new(PayloadU8::new(ms.to_vec())),
             extended_ms: false,
             client_cert_chain,
             alpn: alpn.map(PayloadU8::new),
@@ -420,7 +420,7 @@ mod tests {
             None,
             ProtocolVersion::TLSv1_3,
             CipherSuite::TLS13_AES_128_GCM_SHA256,
-            vec![1, 2, 3],
+            &[1, 2, 3],
             None,
             None,
             vec![4, 5, 6],

rustls/src/server/tls12.rs

@@ -751,13 +751,12 @@ fn get_server_connection_value_tls12(
     time_now: UnixTime,
 ) -> persist::ServerSessionValue {
     let version = ProtocolVersion::TLSv1_2;
-    let secret = secrets.get_master_secret();
 
     let mut v = persist::ServerSessionValue::new(
         cx.data.sni.as_ref(),
         version,
         secrets.suite().common.suite,
-        secret,
+        secrets.master_secret(),
         cx.common.peer_certificates.clone(),
         cx.common.alpn_protocol.clone(),
         cx.data.resumption_data.clone(),

rustls/src/server/tls13.rs

@@ -1067,7 +1067,7 @@ fn get_server_session_value(
         cx.data.sni.as_ref(),
         version,
         suite.common.suite,
-        secret.as_ref().to_vec(),
+        secret.as_ref(),
         cx.common.peer_certificates.clone(),
         cx.common.alpn_protocol.clone(),
         cx.data.resumption_data.clone(),

rustls/src/tls12/mod.rs

@@ -193,10 +193,8 @@ impl ConnectionSecrets {
         self.suite
     }
 
-    pub(crate) fn get_master_secret(&self) -> Vec<u8> {
-        let mut ret = Vec::new();
-        ret.extend_from_slice(&self.master_secret);
-        ret
+    pub(crate) fn master_secret(&self) -> &[u8] {
+        &self.master_secret[..]
     }
 
     fn make_verify_data(&self, handshake_hash: &hash::Output, label: &[u8]) -> Vec<u8> {