pk: Remove obsoleted functions

`Cipher.to_PEM()` and `Cipher.to_DER()` have been marked obsolete
for some time now.  Use the `export*` methods instead.

ChangeLog

@@ -1,3 +1,7 @@
+[next]
+
+* pk: Remove obsoleted to_PEM and to_DER functions.
+
 [2.9.2] - 2024-02-18
 
 * ci: Update wheels to mbedtls 2.28.7

src/mbedtls/pk.pyi

@@ -76,6 +76,9 @@ class CipherBase:
     ) -> None: ...
     def __hash__(self) -> int: ...
     def __eq__(self, other: object) -> bool: ...
+    def __str__(self) -> _PEM: ...
+    def __bytes__(self) -> _DER: ...
+    def to_bytes(self) -> _DER: ...
     @classmethod
     def from_buffer(
         cls: Type[_TCipherBase],
@@ -110,11 +113,6 @@ class CipherBase:
     ) -> bool: ...
     def encrypt(self, message: bytes) -> bytes: ...
     def decrypt(self, message: bytes) -> bytes: ...
-    def to_PEM(self) -> KeyPair: ...
-    def __str__(self) -> _PEM: ...
-    def to_DER(self) -> KeyPair: ...
-    def to_bytes(self) -> _DER: ...
-    def __bytes__(self) -> _DER: ...
 
 class RSA(CipherBase):
     def __init__(

src/mbedtls/pk.pyx

@@ -225,6 +225,16 @@ cdef class CipherBase:
         elif not (self._has_private() and other._has_private()):
             return other.export_public_key() == self.export_public_key()
 
+    def __str__(self):
+        return self.export_key(format="PEM")
+
+    def __bytes__(self):
+        return self.to_bytes()
+
+    def to_bytes(self):
+        """Return the private key in DER format."""
+        return self.export_key(format="DER")
+
     @classmethod
     def from_buffer(
         cls,
@@ -501,46 +511,6 @@ cdef class CipherBase:
             return self._public_to_PEM()
         raise ValueError(format)
 
-    def to_PEM(self):
-        """Return the RSA in PEM format.
-
-        Warning:
-            This function is obsolete.
-
-        Return:
-            tuple(str, str): The private key and the public key.
-
-        See Also:
-            export_key(), export_public_key()
-
-        """
-        return KeyPair(self.export_key("PEM"), self.export_public_key("PEM"))
-
-    def __str__(self):
-        return self.export_key(format="PEM")
-
-    def to_DER(self):
-        """Return the RSA in DER format.
-
-        Warning:
-            This function is obsolete.
-
-        Return:
-            tuple(bytes, bytes): The private key and the public key.
-
-        See Also:
-            export_key(), export_public_key()
-
-        """
-        return KeyPair(self.export_key("DER"), self.export_public_key("DER"))
-
-    def to_bytes(self):
-        """Return the private key in DER format."""
-        return self.export_key(format="DER")
-
-    def __bytes__(self):
-        return self.to_bytes()
-
 
 cdef class RSA(CipherBase):
 

tests/test_pk.py

@@ -173,7 +173,6 @@ def test_export_private_key(
         assert pem.startswith(f"-----BEGIN {cipher_tag} PRIVATE KEY-----\n")
         assert pem.endswith(f"-----END {cipher_tag} PRIVATE KEY-----\n")
         assert pem == str(cipher)
-        assert pem == cipher.to_PEM().private
         assert cipher == type(cipher).from_PEM(pem)
 
     @pytest.mark.parametrize(