diff --git a/securesystemslib/signer/_key.py b/securesystemslib/signer/_key.py
index acbf646b..bd631925 100644
--- a/securesystemslib/signer/_key.py
+++ b/securesystemslib/signer/_key.py
@@ -21,6 +21,8 @@
     from cryptography.exceptions import InvalidSignature
     from cryptography.hazmat.primitives.asymmetric.ec import (
         ECDSA,
+        SECP256R1,
+        SECP384R1,
         EllipticCurvePublicKey,
     )
     from cryptography.hazmat.primitives.asymmetric.ed25519 import (
@@ -245,32 +247,39 @@ def _crypto_key(self) -> "PublicKeyTypes":
         return load_pem_public_key(public_bytes)
 
     @staticmethod
-    def _get_keytype_for_crypto_key(public_key: "PublicKeyTypes") -> str:
-        """Helper to return keytype for pyca/cryptography public key."""
-        if isinstance(public_key, RSAPublicKey):
-            return "rsa"
+    def _from_crypto(public_key: "PublicKeyTypes") -> Tuple[str, str, str]:
+        """Return tuple of keytype, default scheme and serialized public key
+        value for the passed public key.
 
-        if isinstance(public_key, EllipticCurvePublicKey):
-            return "ecdsa"
+        Raise ValueError if public key is not supported.
+        """
 
-        if isinstance(public_key, Ed25519PublicKey):
-            return "ed25519"
+        def _raw() -> str:
+            return public_key.public_bytes(
+                encoding=Encoding.Raw, format=PublicFormat.Raw
+            ).hex()
 
-        raise ValueError(f"unsupported 'public_key' type {type(public_key)}")
+        def _pem() -> str:
+            return public_key.public_bytes(
+                encoding=Encoding.PEM, format=PublicFormat.SubjectPublicKeyInfo
+            ).decode()
 
-    @staticmethod
-    def _get_default_scheme(keytype: str) -> str:
-        """Helper to return default scheme for keytype."""
-        if keytype == "rsa":
-            return "rsassa-pss-sha256"
+        if isinstance(public_key, RSAPublicKey):
+            return "rsa", "rsassa-pss-sha256", _pem()
 
-        if keytype == "ecdsa":
-            return "ecdsa-sha2-nistp256"
+        if isinstance(public_key, EllipticCurvePublicKey):
+            if isinstance(public_key.curve, SECP256R1):
+                return "ecdsa", "ecdsa-sha2-nistp256", _pem()
 
-        if keytype == "ed25519":
-            return "ed25519"
+            if isinstance(public_key.curve, SECP384R1):
+                return "ecdsa", "ecdsa-sha2-nistp384", _pem()
 
-        raise ValueError(f"unsupported 'keytype' {keytype}")
+            raise ValueError(f"unsupported curve '{public_key.curve.name}'")
+
+        if isinstance(public_key, Ed25519PublicKey):
+            return "ed25519", "ed25519", _raw()
+
+        raise ValueError(f"unsupported key '{type(public_key)}'")
 
     @classmethod
     def from_crypto(
@@ -285,7 +294,8 @@ def from_crypto(
             public_key: pyca/cryptography public key object.
             keyid: Key identifier. If not passed, a default keyid is computed.
             scheme: SSlibKey signing scheme. Defaults are "rsassa-pss-sha256",
-                "ecdsa-sha2-nistp256", and "ed25519" according to the keytype
+                "ecdsa-sha2-nistp256", "ecdsa-sha2-nistp384" and "ed25519"
+                according to the keytype.
 
         Raises:
             UnsupportedLibraryError: pyca/cryptography not installed
@@ -298,21 +308,10 @@ def from_crypto(
         if CRYPTO_IMPORT_ERROR:
             raise UnsupportedLibraryError(CRYPTO_IMPORT_ERROR)
 
-        keytype = cls._get_keytype_for_crypto_key(public_key)
-        if not scheme:
-            scheme = cls._get_default_scheme(keytype)
-
-        if keytype in ["rsa", "ecdsa"]:
-            pem: bytes = public_key.public_bytes(
-                encoding=Encoding.PEM, format=PublicFormat.SubjectPublicKeyInfo
-            )
-            public_key_value = pem.decode()
+        keytype, default_scheme, public_key_value = cls._from_crypto(public_key)
 
-        else:  # ed25519
-            raw: bytes = public_key.public_bytes(
-                encoding=Encoding.Raw, format=PublicFormat.Raw
-            )
-            public_key_value = raw.hex()
+        if not scheme:
+            scheme = default_scheme
 
         keyval = {"public": public_key_value}
 
diff --git a/tests/data/pems/ecdsa_secp384r1_private.pem b/tests/data/pems/ecdsa_secp384r1_private.pem
new file mode 100644
index 00000000..9f5cdf6a
--- /dev/null
+++ b/tests/data/pems/ecdsa_secp384r1_private.pem
@@ -0,0 +1,6 @@
+-----BEGIN PRIVATE KEY-----
+MIG2AgEAMBAGByqGSM49AgEGBSuBBAAiBIGeMIGbAgEBBDCcHGK5kIyeNu1WvNqh
+02kwOdu5BFuYptulHFJRWiaIXrC9nwgtWDjNco8BTIKYdTmhZANiAASSwAbzSctS
+Sw4NMRQFM8kk9g3Rt/GGSuvaGXKiR9EbiQNixFE3zq9bDENNbuqFY1k8WEkwnEea
+8ewJsvP8gXuF2jxe/+9E7gxUdvCrR+JbOdS+RmjAcLl8fYQS80XVHm0=
+-----END PRIVATE KEY-----
diff --git a/tests/data/pems/ecdsa_secp384r1_public.pem b/tests/data/pems/ecdsa_secp384r1_public.pem
new file mode 100644
index 00000000..24c1ab74
--- /dev/null
+++ b/tests/data/pems/ecdsa_secp384r1_public.pem
@@ -0,0 +1,5 @@
+-----BEGIN PUBLIC KEY-----
+MHYwEAYHKoZIzj0CAQYFK4EEACIDYgAEksAG80nLUksODTEUBTPJJPYN0bfxhkrr
+2hlyokfRG4kDYsRRN86vWwxDTW7qhWNZPFhJMJxHmvHsCbLz/IF7hdo8Xv/vRO4M
+VHbwq0fiWznUvkZowHC5fH2EEvNF1R5t
+-----END PUBLIC KEY-----
diff --git a/tests/test_signer.py b/tests/test_signer.py
index 84fa2958..73cdb99e 100644
--- a/tests/test_signer.py
+++ b/tests/test_signer.py
@@ -299,16 +299,25 @@ def test_from_crypto(self):
                 "rsa",
                 "rsassa-pss-sha256",
                 "2f685fa7546f1856b123223ab086b3def14c89d24eef18f49c32508c2f60e241",
+                "rsa_public.pem",
             ),
             (
                 "ecdsa",
                 "ecdsa-sha2-nistp256",
                 "50d7e110ad65f3b2dba5c3cfc8c5ca259be9774cc26be3410044ffd4be3aa5f3",
+                "ecdsa_public.pem",
+            ),
+            (
+                "ecdsa",
+                "ecdsa-sha2-nistp384",
+                "0155661bdf705f621a74f55eef36c9ae041e456141eced7a45d4a1f75ded9ac0",
+                "ecdsa_secp384r1_public.pem",
             ),
             (
                 "ed25519",
                 "ed25519",
                 "c6d8bf2e4f48b41ac2ce8eca21415ca8ef68c133b47fc33df03d4070a7e1e9cc",
+                "ed25519_public.pem",
             ),
         ]
 
@@ -319,8 +328,8 @@ def _from_file(path):
             crypto_key = load_pem_public_key(pem)
             return crypto_key
 
-        for keytype, default_scheme, default_keyid in test_data:
-            crypto_key = _from_file(PEMS_DIR / f"{keytype}_public.pem")
+        for keytype, default_scheme, default_keyid, fname in test_data:
+            crypto_key = _from_file(PEMS_DIR / fname)
             key = SSlibKey.from_crypto(crypto_key)
             self.assertEqual(key.keytype, keytype)
             self.assertEqual(key.scheme, default_scheme)