diff --git a/securesystemslib/signer/_crypto_signer.py b/securesystemslib/signer/_crypto_signer.py
index 4ddef2b4..4bba130c 100644
--- a/securesystemslib/signer/_crypto_signer.py
+++ b/securesystemslib/signer/_crypto_signer.py
@@ -2,7 +2,7 @@
 
 import logging
 from dataclasses import astuple, dataclass
-from typing import Any, Dict, Optional, Union
+from typing import Optional, Union
 from urllib import parse
 
 from securesystemslib.exceptions import UnsupportedLibraryError
@@ -189,28 +189,6 @@ def __init__(
     def public_key(self) -> Key:
         return self._public_key
 
-    @classmethod
-    def from_securesystemslib_key(
-        cls, key_dict: Dict[str, Any]
-    ) -> "CryptoSigner":
-        """Factory to create CryptoSigner from securesystemslib private key dict."""
-        private = key_dict["keyval"]["private"]
-        public_key = SSlibKey.from_securesystemslib_key(key_dict)
-
-        private_key: PrivateKeyTypes
-        if public_key.keytype in ["rsa"] + _ECDSA_KEYTYPES:
-            private_key = load_pem_private_key(private.encode(), password=None)
-
-        elif public_key.keytype == "ed25519":
-            private_key = Ed25519PrivateKey.from_private_bytes(
-                bytes.fromhex(private)
-            )
-
-        else:
-            raise ValueError(f"unsupported keytype: {public_key.keytype}")
-
-        return CryptoSigner(private_key, public_key)
-
     @classmethod
     def from_priv_key_uri(
         cls,
diff --git a/securesystemslib/signer/_key.py b/securesystemslib/signer/_key.py
index acbf646b..11ceb3f0 100644
--- a/securesystemslib/signer/_key.py
+++ b/securesystemslib/signer/_key.py
@@ -198,34 +198,6 @@ def verify_signature(self, signature: Signature, data: bytes) -> None:
 class SSlibKey(Key):
     """Key implementation for RSA, Ed25519, ECDSA keys"""
 
-    def to_securesystemslib_key(self) -> Dict[str, Any]:
-        """Internal helper, returns a classic securesystemslib keydict.
-
-        .. deprecated:: 0.28.0
-            Please use ``CryptoSigner`` instead of securesystemslib keydicts.
-        """
-        return {
-            "keyid": self.keyid,
-            "keytype": self.keytype,
-            "scheme": self.scheme,
-            "keyval": self.keyval,
-        }
-
-    @classmethod
-    def from_securesystemslib_key(cls, key_dict: Dict[str, Any]) -> "SSlibKey":
-        """Constructor from classic securesystemslib keydict
-
-        .. deprecated:: 0.28.0
-            Please use ``CryptoSigner`` instead of securesystemslib keydicts.
-        """
-        # ensure possible private keys are not included in keyval
-        return SSlibKey(
-            key_dict["keyid"],
-            key_dict["keytype"],
-            key_dict["scheme"],
-            {"public": key_dict["keyval"]["public"]},
-        )
-
     @classmethod
     def from_dict(cls, keyid: str, key_dict: Dict[str, Any]) -> "SSlibKey":
         keytype, scheme, keyval = cls._from_dict(key_dict)