From e150d3153af30530ce61d751bc166e099f1ead7a Mon Sep 17 00:00:00 2001
From: Khwahish Patel <khwahish.p1@ahduni.edu.in>
Date: Wed, 5 Mar 2025 12:29:52 +0530
Subject: [PATCH] rufuse large RSA keys

---
 libp2p/crypto/rsa.py | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/libp2p/crypto/rsa.py b/libp2p/crypto/rsa.py
index 5f14ce95..6673919a 100644
--- a/libp2p/crypto/rsa.py
+++ b/libp2p/crypto/rsa.py
@@ -9,6 +9,9 @@ from Crypto.Signature import (
     pkcs1_15,
 )
 
+from libp2p.crypto.exceptions import (
+    CryptographyError,
+)
 from libp2p.crypto.keys import (
     KeyPair,
     KeyType,
@@ -16,9 +19,26 @@ from libp2p.crypto.keys import (
     PublicKey,
 )
 
+MAX_RSA_KEY_SIZE = 4096
+
+
+def validate_rsa_key_size(key: RsaKey) -> None:
+    """
+    Validate that an RSA key's size is within acceptable bounds.
+
+    :param key: The RSA key to validate
+    :raises CryptographyError: If the key size exceeds the maximum allowed size
+    """
+    key_size = key.size_in_bits()
+    if key_size > MAX_RSA_KEY_SIZE:
+        msg = f"RSA key size {key_size} "
+        msg += f"exceeds maximum allowed size {MAX_RSA_KEY_SIZE}"
+        raise CryptographyError(msg)
+
 
 class RSAPublicKey(PublicKey):
     def __init__(self, impl: RsaKey) -> None:
+        validate_rsa_key_size(impl)
         self.impl = impl
 
     def to_bytes(self) -> bytes:
@@ -27,6 +47,7 @@ class RSAPublicKey(PublicKey):
     @classmethod
     def from_bytes(cls, key_bytes: bytes) -> "RSAPublicKey":
         rsakey = RSA.import_key(key_bytes)
+        validate_rsa_key_size(rsakey)
         return cls(rsakey)
 
     def get_type(self) -> KeyType:
@@ -43,10 +64,15 @@ class RSAPublicKey(PublicKey):
 
 class RSAPrivateKey(PrivateKey):
     def __init__(self, impl: RsaKey) -> None:
+        validate_rsa_key_size(impl)
         self.impl = impl
 
     @classmethod
     def new(cls, bits: int = 2048, e: int = 65537) -> "RSAPrivateKey":
+        if bits > MAX_RSA_KEY_SIZE:
+            msg = f"Requested RSA key size {bits} "
+            msg += f"exceeds maximum allowed size {MAX_RSA_KEY_SIZE}"
+            raise CryptographyError(msg)
         private_key_impl = RSA.generate(bits, e=e)
         return cls(private_key_impl)