diff --git a/native/rust/cose_openssl/Cargo.toml b/native/rust/cose_openssl/Cargo.toml
index 6486a635..7ab661ea 100644
--- a/native/rust/cose_openssl/Cargo.toml
+++ b/native/rust/cose_openssl/Cargo.toml
@@ -14,5 +14,5 @@ warnings = "deny"
 
 [dependencies]
 openssl-sys = "0.9"
-cborrs = { git = "https://github.com/project-everest/everparse.git", tag = "v2026.02.25" }
-cborrs-nondet = { git = "https://github.com/project-everest/everparse.git", tag = "v2026.02.25" }
+cborrs = { git = "https://github.com/project-everest/everparse.git", rev = "f4cd5ffa183edd5cc824d66588012bcf8d0bdccd" } # v2026.02.25
+cborrs-nondet = { git = "https://github.com/project-everest/everparse.git", rev = "f4cd5ffa183edd5cc824d66588012bcf8d0bdccd" } # v2026.02.25
diff --git a/native/rust/cose_openssl/src/cbor.rs b/native/rust/cose_openssl/src/cbor.rs
index 9cc70922..ba6c3850 100644
--- a/native/rust/cose_openssl/src/cbor.rs
+++ b/native/rust/cose_openssl/src/cbor.rs
@@ -287,6 +287,28 @@ fn serialize_det(item: CborDet) -> Result<Vec<u8>, String> {
     Ok(buf)
 }
 
+/// A CBOR item that borrows its data, for zero-copy serialization.
+pub enum CborSlice<'a> {
+    TextStr(&'a str),
+    ByteStr(&'a [u8]),
+}
+
+/// Serialize a CBOR array of borrowed items without intermediate copies.
+pub fn serialize_array(items: &[CborSlice<'_>]) -> Result<Vec<u8>, String> {
+    let mut raw: Vec<CborDet<'_>> = items
+        .iter()
+        .map(|item| match item {
+            CborSlice::TextStr(s) => cbor_det_mk_text_string(s)
+                .ok_or("Failed to make CBOR text string".to_string()),
+            CborSlice::ByteStr(b) => cbor_det_mk_byte_string(b)
+                .ok_or("Failed to make CBOR byte string".to_string()),
+        })
+        .collect::<Result<_, _>>()?;
+    let array = cbor_det_mk_array(&mut raw)
+        .ok_or("Failed to build CBOR array".to_string())?;
+    serialize_det(array)
+}
+
 impl std::fmt::Debug for CborValue {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         match self {
diff --git a/native/rust/cose_openssl/src/cose.rs b/native/rust/cose_openssl/src/cose.rs
index 57417511..5ea1ce31 100644
--- a/native/rust/cose_openssl/src/cose.rs
+++ b/native/rust/cose_openssl/src/cose.rs
@@ -1,4 +1,4 @@
-use crate::cbor::CborValue;
+use crate::cbor::{CborSlice, CborValue, serialize_array};
 use crate::ossl_wrappers::{
     EvpKey, KeyType, WhichEC, WhichRSA, ecdsa_der_to_fixed, ecdsa_fixed_to_der,
     rsa_pss_md_for_cose_alg,
@@ -56,14 +56,18 @@ fn insert_alg_value(
 
 /// To-be-signed (TBS).
 /// https://www.rfc-editor.org/rfc/rfc9052.html#section-4.4.
+///
+/// Uses `serialize_array` with borrowed slices to avoid copying
+/// `phdr` and `payload` into intermediate `Vec<u8>`s. These can
+/// be large (payload especially), so we serialize directly from
+/// the caller's buffers.
 fn sig_structure(phdr: &[u8], payload: &[u8]) -> Result<Vec<u8>, String> {
-    CborValue::Array(vec![
-        CborValue::TextString(SIG_STRUCTURE1_CONTEXT.to_string()),
-        CborValue::ByteString(phdr.to_vec()),
-        CborValue::ByteString(vec![]),
-        CborValue::ByteString(payload.to_vec()),
+    serialize_array(&[
+        CborSlice::TextStr(SIG_STRUCTURE1_CONTEXT),
+        CborSlice::ByteStr(phdr),
+        CborSlice::ByteStr(&[]),
+        CborSlice::ByteStr(payload),
     ])
-    .to_bytes()
 }
 
 /// Produce a COSE_Sign1 envelope.
diff --git a/native/rust/cose_openssl/src/sign.rs b/native/rust/cose_openssl/src/sign.rs
index 69b7ce9f..32020189 100644
--- a/native/rust/cose_openssl/src/sign.rs
+++ b/native/rust/cose_openssl/src/sign.rs
@@ -33,7 +33,7 @@ fn sign_with_ctx(
             msg.len(),
         );
         if res != 1 {
-            return Err(format!("Failed to signature size, err: {}", res));
+            return Err(format!("Failed to get signature size, err: {}", res));
         }
 
         let mut sig = vec![0u8; sig_size];