fix: reject invalid RSA exponents before calling OpenSSL

RSA.xs

@@ -582,6 +582,8 @@ generate_key(proto, bitsSV, exponent = 65537)
     int error = 0;
 #endif
   CODE:
+    if (exponent < 3 || (exponent % 2) == 0)
+        croak("RSA exponent must be odd and >= 3 (got %lu)", exponent);
     e = BN_new();
     BN_set_word(e, exponent);
 #if OPENSSL_VERSION_NUMBER < 0x00908000L

t/key_lifecycle.t

@@ -11,7 +11,7 @@ my $HAS_BIGNUM = eval { require Crypt::OpenSSL::Bignum; 1 } ? 1 : 0;
 
 # skip() reports skipped tests which count toward total, so plan must
 # always include them regardless of whether Bignum is available.
-plan tests => 9 + 14 + 20 + 2;
+plan tests => 9 + 14 + 20 + 2 + 4;
 
 # --- Cross-key operations ---
 # Sign with key1, verify with key2 — should return false, not croak.
@@ -206,3 +206,21 @@ like( $@, qr/modulus and public key must be provided/,
 eval { Crypt::OpenSSL::RSA->_new_key_from_parameters(0, 0, 0, 0, 0) };
 like( $@, qr/modulus and public key must be provided/,
     "croak when n=0 and e=0 (missing required params)" );
+
+# --- Invalid exponent rejection (prevents RSA_generate_key_ex hang on OpenSSL 1.1.x) ---
+
+eval { Crypt::OpenSSL::RSA->generate_key(2048, 2) };
+like( $@, qr/RSA exponent must be odd and >= 3/,
+    "generate_key croaks on even exponent (2)" );
+
+eval { Crypt::OpenSSL::RSA->generate_key(2048, 1) };
+like( $@, qr/RSA exponent must be odd and >= 3/,
+    "generate_key croaks on exponent 1" );
+
+eval { Crypt::OpenSSL::RSA->generate_key(2048, 0) };
+like( $@, qr/RSA exponent must be odd and >= 3/,
+    "generate_key croaks on exponent 0" );
+
+eval { Crypt::OpenSSL::RSA->generate_key(2048, 100) };
+like( $@, qr/RSA exponent must be odd and >= 3/,
+    "generate_key croaks on even exponent (100)" );