diff --git a/libs/bssl/error/src/lib.rs b/libs/bssl/error/src/lib.rs
index 0bdb821..822e02d 100644
--- a/libs/bssl/error/src/lib.rs
+++ b/libs/bssl/error/src/lib.rs
@@ -88,6 +88,7 @@
     EC_KEY_new_by_curve_name,
     EC_KEY_set_public_key_affine_coordinates,
     EC_POINT_get_affine_coordinates,
+    ECDSA_SIG_from_bytes,
     ECDSA_SIG_new,
     ECDSA_SIG_set0,
     ECDSA_sign,
diff --git a/libs/bssl/src/ec_key.rs b/libs/bssl/src/ec_key.rs
index 9eb5e5c..3e2e382 100644
--- a/libs/bssl/src/ec_key.rs
+++ b/libs/bssl/src/ec_key.rs
@@ -23,9 +23,10 @@
 use bssl_avf_error::{ApiName, Error, Result};
 use bssl_sys::{
     i2d_ECDSA_SIG, BN_bin2bn, BN_bn2bin_padded, BN_clear_free, BN_new, CBB_flush, CBB_len,
-    ECDSA_SIG_free, ECDSA_SIG_new, ECDSA_SIG_set0, ECDSA_sign, ECDSA_size, ECDSA_verify,
-    EC_GROUP_get_curve_name, EC_GROUP_new_by_curve_name, EC_KEY_check_key, EC_KEY_free,
-    EC_KEY_generate_key, EC_KEY_get0_group, EC_KEY_get0_public_key, EC_KEY_marshal_private_key,
+    ECDSA_SIG_free, ECDSA_SIG_from_bytes, ECDSA_SIG_get0_r, ECDSA_SIG_get0_s, ECDSA_SIG_new,
+    ECDSA_SIG_set0, ECDSA_sign, ECDSA_size, ECDSA_verify, EC_GROUP_get_curve_name,
+    EC_GROUP_new_by_curve_name, EC_KEY_check_key, EC_KEY_free, EC_KEY_generate_key,
+    EC_KEY_get0_group, EC_KEY_get0_public_key, EC_KEY_marshal_private_key,
     EC_KEY_new_by_curve_name, EC_KEY_parse_private_key, EC_KEY_set_public_key_affine_coordinates,
     EC_POINT_get_affine_coordinates, NID_X9_62_prime256v1, NID_secp384r1, BIGNUM, ECDSA_SIG,
     EC_GROUP, EC_KEY, EC_POINT,
@@ -165,11 +166,11 @@
         check_int_result(ret, ApiName::ECDSA_verify)
     }
 
-    /// Verifies the NIST-encoded (R | S) ECDSA `signature` of the `digest` with the current
-    /// `EcKey`.
+    /// Verifies the COSE-encoded (R | S, see RFC8152) ECDSA `signature` of the `digest` with the
+    /// current `EcKey`.
     ///
     /// Returns Ok(()) if the verification succeeds, otherwise an error will be returned.
-    pub fn ecdsa_verify_nist(&self, signature: &[u8], digest: &[u8]) -> Result<()> {
+    pub fn ecdsa_verify_cose(&self, signature: &[u8], digest: &[u8]) -> Result<()> {
         let signature = ec_cose_signature_to_der(signature)?;
         self.ecdsa_verify_der(&signature, digest)
     }
@@ -177,7 +178,7 @@
     /// Signs the `digest` with the current `EcKey` using ECDSA.
     ///
     /// Returns the DER-encoded ECDSA signature.
-    pub fn ecdsa_sign(&self, digest: &[u8]) -> Result<Vec<u8>> {
+    pub fn ecdsa_sign_der(&self, digest: &[u8]) -> Result<Vec<u8>> {
         // The `type` argument should be 0 as required in the BoringSSL spec.
         const TYPE: i32 = 0;
 
@@ -204,6 +205,15 @@
         }
     }
 
+    /// Signs the `digest` with the current `EcKey` using ECDSA.
+    ///
+    /// Returns the COSE-encoded (R | S, see RFC8152) ECDSA signature.
+    pub fn ecdsa_sign_cose(&self, digest: &[u8]) -> Result<Vec<u8>> {
+        let signature = self.ecdsa_sign_der(digest)?;
+        let coord_bytes = self.ec_group()?.affine_coordinate_size()?;
+        ec_der_signature_to_cose(&signature, coord_bytes)
+    }
+
     /// Returns the maximum size of an ECDSA signature using the current `EcKey`.
     fn ecdsa_size(&self) -> Result<usize> {
         // SAFETY: This function only reads the `EC_KEY` that has been initialized
@@ -335,13 +345,19 @@
     }
 }
 
-/// Convert a R | S format NIST signature to a DER-encoded form.
+/// Convert a COSE format (R | S) ECDSA signature to a DER-encoded form.
 fn ec_cose_signature_to_der(signature: &[u8]) -> Result<Vec<u8>> {
     let mut ec_sig = EcSignature::new()?;
-    ec_sig.load_from_nist(signature)?;
+    ec_sig.load_from_cose(signature)?;
     ec_sig.to_der()
 }
 
+/// Convert a DER-encoded signature to COSE format (R | S).
+fn ec_der_signature_to_cose(signature: &[u8], coord_bytes: usize) -> Result<Vec<u8>> {
+    let ec_sig = EcSignature::new_from_der(signature)?;
+    ec_sig.to_cose(coord_bytes)
+}
+
 /// Wrapper for an `ECDSA_SIG` object representing an EC signature.
 struct EcSignature(NonNull<ECDSA_SIG>);
 
@@ -356,8 +372,8 @@
         Ok(Self(signature))
     }
 
-    /// Populate the signature parameters from a NIST encoding (R | S).
-    fn load_from_nist(&mut self, signature: &[u8]) -> Result<()> {
+    /// Populate the signature parameters from a COSE encoding (R | S).
+    fn load_from_cose(&mut self, signature: &[u8]) -> Result<()> {
         let coord_bytes = signature.len() / 2;
         if signature.len() != 2 * coord_bytes {
             return Err(Error::InternalError);
@@ -379,6 +395,44 @@
         Ok(())
     }
 
+    fn to_cose(&self, coord_bytes: usize) -> Result<Vec<u8>> {
+        let mut result = vec![0u8; coord_bytes.checked_mul(2).unwrap()];
+        let (r_bytes, s_bytes) = result.split_at_mut(coord_bytes);
+
+        // SAFETY: The ECDSA_SIG was properly allocated and not yet freed. Always returns a valid
+        // non-null, non-owning pointer.
+        let r = unsafe { ECDSA_SIG_get0_r(self.0.as_ptr()) };
+        check_int_result(
+            // SAFETY: The r pointer is known to be valid. Only writes within the destination
+            // slice.
+            unsafe { BN_bn2bin_padded(r_bytes.as_mut_ptr(), r_bytes.len(), r) },
+            ApiName::BN_bn2bin_padded,
+        )?;
+
+        // SAFETY: The ECDSA_SIG was properly allocated and not yet freed. Always returns a valid
+        // non-null, non-owning pointer.
+        let s = unsafe { ECDSA_SIG_get0_s(self.0.as_ptr()) };
+        check_int_result(
+            // SAFETY: The r pointer is known to be valid. Only writes within the destination
+            // slice.
+            unsafe { BN_bn2bin_padded(s_bytes.as_mut_ptr(), s_bytes.len(), s) },
+            ApiName::BN_bn2bin_padded,
+        )?;
+
+        Ok(result)
+    }
+
+    /// Populate the signature parameters from a DER encoding
+    fn new_from_der(signature: &[u8]) -> Result<Self> {
+        // SAFETY: Only reads within the bounds of the slice. Returns a pointer to a new ECDSA_SIG
+        // which we take ownership of, or null on error which we check.
+        let signature = unsafe { ECDSA_SIG_from_bytes(signature.as_ptr(), signature.len()) };
+
+        let signature = NonNull::new(signature)
+            .ok_or_else(|| to_call_failed_error(ApiName::ECDSA_SIG_from_bytes))?;
+        Ok(Self(signature))
+    }
+
     /// Return the signature encoded as DER.
     fn to_der(&self) -> Result<Vec<u8>> {
         // SAFETY: The ECDSA_SIG was properly allocated and not yet freed. Null is a valid
diff --git a/libs/bssl/tests/eckey_test.rs b/libs/bssl/tests/eckey_test.rs
index 00ed6c5..0fc78a1 100644
--- a/libs/bssl/tests/eckey_test.rs
+++ b/libs/bssl/tests/eckey_test.rs
@@ -87,7 +87,7 @@
     let digest = digester.digest(MESSAGE1)?;
     assert_eq!(digest, sha256(MESSAGE1)?);
 
-    let signature = ec_key.ecdsa_sign(&digest)?;
+    let signature = ec_key.ecdsa_sign_der(&digest)?;
     ec_key.ecdsa_verify_der(&signature, &digest)?;
     // Building a `PKey` from a temporary `CoseKey` should work as the lifetime
     // of the `PKey` is not tied to the lifetime of the `CoseKey`.
@@ -102,7 +102,7 @@
     let digester = Digester::sha384();
     let digest = digester.digest(MESSAGE1)?;
 
-    let signature = ec_key.ecdsa_sign(&digest)?;
+    let signature = ec_key.ecdsa_sign_der(&digest)?;
     ec_key.ecdsa_verify_der(&signature, &digest)?;
     let pkey = PKey::from_cose_public_key(&ec_key.cose_public_key()?)?;
     pkey.verify(&signature, MESSAGE1, Some(digester))
@@ -113,7 +113,7 @@
     let mut ec_key1 = EcKey::new_p256()?;
     ec_key1.generate_key()?;
     let digest = sha256(MESSAGE1)?;
-    let signature = ec_key1.ecdsa_sign(&digest)?;
+    let signature = ec_key1.ecdsa_sign_der(&digest)?;
 
     let mut ec_key2 = EcKey::new_p256()?;
     ec_key2.generate_key()?;
@@ -134,7 +134,7 @@
     let mut ec_key = EcKey::new_p256()?;
     ec_key.generate_key()?;
     let digest1 = sha256(MESSAGE1)?;
-    let signature = ec_key.ecdsa_sign(&digest1)?;
+    let signature = ec_key.ecdsa_sign_der(&digest1)?;
     let digest2 = sha256(MESSAGE2)?;
 
     let err = ec_key.ecdsa_verify_der(&signature, &digest2).unwrap_err();
@@ -142,3 +142,42 @@
     assert_eq!(expected_err, err);
     Ok(())
 }
+
+#[test]
+fn ecdsa_cose_signing_and_verification_succeed() -> Result<()> {
+    let digest = sha256(MESSAGE1)?;
+    let mut ec_key = EcKey::new_p256()?;
+    ec_key.generate_key()?;
+
+    let signature = ec_key.ecdsa_sign_cose(&digest)?;
+    ec_key.ecdsa_verify_cose(&signature, &digest)?;
+    assert_eq!(signature.len(), 64);
+    Ok(())
+}
+
+#[test]
+fn verifying_ecdsa_cose_signed_with_a_different_message_fails() -> Result<()> {
+    let digest = sha256(MESSAGE1)?;
+    let mut ec_key = EcKey::new_p256()?;
+    ec_key.generate_key()?;
+
+    let signature = ec_key.ecdsa_sign_cose(&digest)?;
+
+    let err = ec_key.ecdsa_verify_cose(&signature, &sha256(MESSAGE2)?).unwrap_err();
+    let expected_err = Error::CallFailed(ApiName::ECDSA_verify, EcdsaError::BadSignature.into());
+    assert_eq!(expected_err, err);
+    Ok(())
+}
+
+#[test]
+fn verifying_ecdsa_cose_signed_as_der_fails() -> Result<()> {
+    let digest = sha256(MESSAGE1)?;
+    let mut ec_key = EcKey::new_p256()?;
+    ec_key.generate_key()?;
+
+    let signature = ec_key.ecdsa_sign_cose(&digest)?;
+    let err = ec_key.ecdsa_verify_der(&signature, &digest).unwrap_err();
+    let expected_err = Error::CallFailed(ApiName::ECDSA_verify, EcdsaError::BadSignature.into());
+    assert_eq!(expected_err, err);
+    Ok(())
+}
diff --git a/service_vm/client_vm_csr/src/lib.rs b/service_vm/client_vm_csr/src/lib.rs
index 512ecaf..0babfff 100644
--- a/service_vm/client_vm_csr/src/lib.rs
+++ b/service_vm/client_vm_csr/src/lib.rs
@@ -100,7 +100,7 @@
             sign(message, cdi_leaf_priv.as_array()).map(|v| v.to_vec())
         })?
         .try_add_created_signature(attestation_key_sig_headers, aad, |message| {
-            ecdsa_sign(message, attestation_key)
+            ecdsa_sign_cose(message, attestation_key)
         })?
         .build();
     Ok(signed_data)
@@ -113,12 +113,18 @@
     CoseSignatureBuilder::new().protected(protected).build()
 }
 
-fn ecdsa_sign(message: &[u8], key: &EcKeyRef<Private>) -> Result<Vec<u8>> {
+fn ecdsa_sign_cose(message: &[u8], key: &EcKeyRef<Private>) -> Result<Vec<u8>> {
     let digest = sha256(message);
     // Passes the digest to `ECDSA_do_sign` as recommended in the spec:
     // https://commondatastorage.googleapis.com/chromium-boringssl-docs/ecdsa.h.html#ECDSA_do_sign
     let sig = EcdsaSig::sign::<Private>(&digest, key)?;
-    Ok(sig.to_der()?)
+    ecdsa_sig_to_cose(&sig)
+}
+
+fn ecdsa_sig_to_cose(signature: &EcdsaSig) -> Result<Vec<u8>> {
+    let mut result = signature.r().to_vec_padded(ATTESTATION_KEY_AFFINE_COORDINATE_SIZE)?;
+    result.extend_from_slice(&signature.s().to_vec_padded(ATTESTATION_KEY_AFFINE_COORDINATE_SIZE)?);
+    Ok(result)
 }
 
 fn get_affine_coordinates(key: &EcKeyRef<Private>) -> Result<(Vec<u8>, Vec<u8>)> {
@@ -175,29 +181,38 @@
         let chain = dice::Chain::from_cbor(&session, &csr.dice_cert_chain)?;
         let public_key = chain.leaf().subject_public_key();
         cose_sign
-            .verify_signature(0, aad, |signature, message| public_key.verify(signature, message))?;
+            .verify_signature(0, aad, |signature, message| public_key.verify(signature, message))
+            .context("Verifying CDI_Leaf_Priv signature")?;
 
         // Checks the second signature is signed with attestation key.
         let attestation_public_key = CoseKey::from_slice(&csr_payload.public_key).unwrap();
         let ec_public_key = to_ec_public_key(&attestation_public_key)?;
-        cose_sign.verify_signature(1, aad, |signature, message| {
-            ecdsa_verify(signature, message, &ec_public_key)
-        })?;
+        cose_sign
+            .verify_signature(1, aad, |signature, message| {
+                ecdsa_verify_cose(signature, message, &ec_public_key)
+            })
+            .context("Verifying attestation key signature")?;
 
         // Verifies that private key and the public key form a valid key pair.
         let message = b"test message";
-        let signature = ecdsa_sign(message, &ec_private_key)?;
-        ecdsa_verify(&signature, message, &ec_public_key)?;
+        let signature = ecdsa_sign_cose(message, &ec_private_key)?;
+        ecdsa_verify_cose(&signature, message, &ec_public_key)
+            .context("Verifying signature with attested key")?;
 
         Ok(())
     }
 
-    fn ecdsa_verify(
+    fn ecdsa_verify_cose(
         signature: &[u8],
         message: &[u8],
         ec_public_key: &EcKeyRef<Public>,
     ) -> Result<()> {
-        let sig = EcdsaSig::from_der(signature)?;
+        let coord_bytes = signature.len() / 2;
+        assert_eq!(signature.len(), coord_bytes * 2);
+
+        let r = BigNum::from_slice(&signature[..coord_bytes])?;
+        let s = BigNum::from_slice(&signature[coord_bytes..])?;
+        let sig = EcdsaSig::from_private_components(r, s)?;
         let digest = sha256(message);
         if sig.verify(&digest, ec_public_key)? {
             Ok(())
diff --git a/service_vm/requests/src/client_vm.rs b/service_vm/requests/src/client_vm.rs
index 00effd7..2aa7113 100644
--- a/service_vm/requests/src/client_vm.rs
+++ b/service_vm/requests/src/client_vm.rs
@@ -66,7 +66,7 @@
     // Verifies the second signature with the public key in the CSR payload.
     let ec_public_key = EcKey::from_cose_public_key_slice(&csr_payload.public_key)?;
     cose_sign.verify_signature(ATTESTATION_KEY_SIGNATURE_INDEX, aad, |signature, message| {
-        ecdsa_verify(&ec_public_key, signature, message)
+        ecdsa_verify_cose(&ec_public_key, signature, message)
     })?;
 
     let subject_public_key_info = PKey::try_from(ec_public_key)?.subject_public_key_info()?;
@@ -110,20 +110,20 @@
                 RequestProcessingError::FailedToDecryptKeyBlob
             })?;
     let ec_private_key = EcKey::from_ec_private_key(private_key.as_slice())?;
-    let signature = ecdsa_sign(&ec_private_key, &tbs_cert.to_der()?)?;
+    let signature = ecdsa_sign_der(&ec_private_key, &tbs_cert.to_der()?)?;
     let certificate = cert::build_certificate(tbs_cert, &signature)?;
     Ok(certificate.to_der()?)
 }
 
-fn ecdsa_verify(key: &EcKey, signature: &[u8], message: &[u8]) -> bssl_avf::Result<()> {
+fn ecdsa_verify_cose(key: &EcKey, signature: &[u8], message: &[u8]) -> bssl_avf::Result<()> {
     // The message was signed with ECDSA with curve P-256 and SHA-256 at the signature generation.
     let digest = sha256(message)?;
-    key.ecdsa_verify_der(signature, &digest)
+    key.ecdsa_verify_cose(signature, &digest)
 }
 
-fn ecdsa_sign(key: &EcKey, message: &[u8]) -> bssl_avf::Result<Vec<u8>> {
+fn ecdsa_sign_der(key: &EcKey, message: &[u8]) -> bssl_avf::Result<Vec<u8>> {
     let digest = sha256(message)?;
-    key.ecdsa_sign(&digest)
+    key.ecdsa_sign_der(&digest)
 }
 
 fn validate_service_vm_dice_chain_length(service_vm_dice_chain: &[Value]) -> Result<()> {
diff --git a/service_vm/requests/src/dice.rs b/service_vm/requests/src/dice.rs
index f4da7ef..247c34e 100644
--- a/service_vm/requests/src/dice.rs
+++ b/service_vm/requests/src/dice.rs
@@ -214,7 +214,7 @@
         if !key_ops.is_empty()
             && !key_ops.contains(&KeyOperation::Assigned(iana::KeyOperation::Verify))
         {
-            error!("Public key does not support verification");
+            error!("Public key does not support verification - key_ops: {key_ops:?}");
             return Err(RequestProcessingError::InvalidDiceChain);
         }
         Ok(Self(key))
@@ -231,7 +231,7 @@
     /// PubKeyEd25519 / PubKeyECDSA256 / PubKeyECDSA384
     ///
     /// The signature should be in the format defined by COSE in RFC 9053 section 2 for the
-    /// specifric algorithm.
+    /// specific algorithm.
     pub(crate) fn verify(&self, signature: &[u8], message: &[u8]) -> Result<()> {
         match &self.0.kty {
             KeyType::Assigned(iana::KeyType::EC2) => {
@@ -249,7 +249,7 @@
                     }
                 };
                 let digest = digester.digest(message)?;
-                Ok(public_key.ecdsa_verify_nist(signature, &digest)?)
+                Ok(public_key.ecdsa_verify_cose(signature, &digest)?)
             }
             KeyType::Assigned(iana::KeyType::OKP) => {
                 let curve_type =