x448 and x25519 should enforce key lengths in backend (#4703)

* x448 and x25519 should enforce key lengths in from_private_bytes

they should also check if the algorithm is supported like the public
bytes class methods do

* oops

* move the checks

2 files changed, 12 insertions, 3 deletions

diff --git a/src/cryptography/hazmat/primitives/asymmetric/x25519.py b/src/cryptography/hazmat/primitives/asymmetric/x25519.py
index 94602261..4e8badf4 100644
--- a/src/cryptography/hazmat/primitives/asymmetric/x25519.py
+++ b/src/cryptography/hazmat/primitives/asymmetric/x25519.py
@@ -22,9 +22,6 @@ class X25519PublicKey(object):
                 _Reasons.UNSUPPORTED_EXCHANGE_ALGORITHM
             )
 
-        if len(data) != 32:
-            raise ValueError("An X25519 public key is 32 bytes long")
-
         return backend.x25519_load_public_bytes(data)
 
     @abc.abstractmethod
@@ -49,6 +46,12 @@ class X25519PrivateKey(object):
     @classmethod
     def from_private_bytes(cls, data):
         from cryptography.hazmat.backends.openssl.backend import backend
+        if not backend.x25519_supported():
+            raise UnsupportedAlgorithm(
+                "X25519 is not supported by this version of OpenSSL.",
+                _Reasons.UNSUPPORTED_EXCHANGE_ALGORITHM
+            )
+
         return backend.x25519_load_private_bytes(data)
 
     @abc.abstractmethod
diff --git a/src/cryptography/hazmat/primitives/asymmetric/x448.py b/src/cryptography/hazmat/primitives/asymmetric/x448.py
index 992ec0fd..475e678f 100644
--- a/src/cryptography/hazmat/primitives/asymmetric/x448.py
+++ b/src/cryptography/hazmat/primitives/asymmetric/x448.py
@@ -46,6 +46,12 @@ class X448PrivateKey(object):
     @classmethod
     def from_private_bytes(cls, data):
         from cryptography.hazmat.backends.openssl.backend import backend
+        if not backend.x448_supported():
+            raise UnsupportedAlgorithm(
+                "X448 is not supported by this version of OpenSSL.",
+                _Reasons.UNSUPPORTED_EXCHANGE_ALGORITHM
+            )
+
         return backend.x448_load_private_bytes(data)
 
     @abc.abstractmethod