mldsa65: UnmarshalBinary does not validate, library panic on op

[karalabe]

TL;DR: https://go.dev/play/p/Pvzisd1kmT_I

When constructing a secret key from binary, any blob is accepted blindly. Later that will result in a panic on any crypto op.

[armfazh]

From the snippet you shared, the Sign function requires to pass a non-nil opts parameter. In #582 , we catch this case.
Besides calling incorrectly this function, are there any issue with key validation?

package main

import (
	"fmt"

	"github.com/cloudflare/circl/sign/mldsa/mldsa65"
)

func main() {
	// Invalid key bytes (from the fuzz crash)
	var b [mldsa65.PrivateKeySize]byte
	b[0] = 0xb0
	b[1] = 0xea
	// ... rest are zeros which is also invalid

	sk := new(mldsa65.PrivateKey)
	if err := sk.UnmarshalBinary(b[:]); err != nil {
		fmt.Println("UnmarshalBinary failed:", err)
		return
	}
	fmt.Println("UnmarshalBinary succeeded")

	// Try to get public key
	pk := sk.Public()
	fmt.Printf("Public key: %T\n", pk)

	// Try to sign
-	sig, err := sk.Sign(nil, []byte("test"), nil)
+	sig, err := sk.Sign(nil, []byte("test"), crypto.Hash(0))
	if err != nil {
		fmt.Println("Sign failed:", err)
		return
	}
	fmt.Printf("Signature length: %d\n", len(sig))
}