crypto/rsa: allow hash.Hash for OAEP and MGF1 to be specified independently for encryption

// This program demonstrates the current limitation of rsa.EncryptOAEP in Go 1.27.1:
// it requires the same hash function for both OAEP and MGF1. The new
// EncryptOAEPWithOptions function, which would allow independent hash
// selection, is not yet available. The code below uses the standard
// EncryptOAEP with a single hash function (sha256) for both roles.

package main

import (
	"crypto/rand"
	"crypto/rsa"
	"crypto/sha256"
	"fmt"
)

func main() {
	// Generate a temporary RSA key pair for demonstration.
	priv, err := rsa.GenerateKey(rand.Reader, 2048)
	if err != nil {
		panic(err)
	}

	// The message to encrypt (e.g., a 256‑bit AES key).
	msg := []byte("example 256‑bit AES key for demonstration")

	// Encrypt using RSA-OAEP with SHA‑256 for both OAEP and MGF1.
	ciphertext, err := rsa.EncryptOAEP(sha256.New(), rand.Reader, &priv.PublicKey, msg, nil)
	if err != nil {
		panic(err)
	}

	// Decrypt to verify correctness.
	plain, err := rsa.DecryptOAEP(sha256.New(), rand.Reader, priv, ciphertext, nil)
	if err != nil {
		panic(err)
	}

	fmt.Printf("original: %s\n", msg)
	fmt.Printf("decrypted: %s\n", plain)
}