crypto/rsa: deprecate PKCS #1 v1.5 encryption

// This program demonstrates the deprecation warning for RSA PKCS#1 v1.5 encryption.
// It uses the standard library only and runs in Go 1.27.1.
// The EncryptPKCS1v15 function still exists but is marked Deprecated.
// The compiler will emit a warning when this function is called.

package main

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

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

	// Message to encrypt; must be shorter than the modulus minus 11 bytes.
	msg := []byte("Hello, RSA PKCS#1 v1.5")

	// Call the deprecated EncryptPKCS1v15 function.
	ciphertext, err := rsa.EncryptPKCS1v15(rand.Reader, &priv.PublicKey, msg)
	if err != nil {
		panic(err)
	}

	// Decrypt the ciphertext using the deprecated DecryptPKCS1v15 function.
	plain, err := rsa.DecryptPKCS1v15(rand.Reader, priv, ciphertext)
	if err != nil {
		panic(err)
	}

	fmt.Printf("Original: %s\nDecrypted: %s\n", msg, plain)
}