~~NOTOC~~
====== Scenario 11.4: Backup chiavi ======

<WRAP round info>
**Categoria:** [[.:start|Gestione chiavi]] \\
**Complessità:** Alta \\
**Prerequisiti:** Chiavi generate, infrastruttura di backup \\
**Tempo stimato:** 25-35 minuti
</WRAP>

----

===== Descrizione =====

Questo scenario descrive il **backup sicuro delle chiavi crittografiche**. Un concetto di backup ben pianificato è fondamentale per la Business Continuity e il Disaster Recovery.

**Strategie di backup:**
  * **Backup crittografato** - AES-256 o PQ-ibrido
  * **Key Splitting** - Shamir's Secret Sharing
  * **Distribuzione geografica** - Più sedi
  * **Backup offline** - Sistemi air-gapped
  * **Backup HSM** - Basato su hardware

----

===== Workflow =====

<mermaid>
flowchart TD
    KEY[Chiave privata] --> ENCRYPT[Crittografare]
    ENCRYPT --> SPLIT{Splitting?}
    SPLIT -->|Sì| SHAMIR[Shamir Split n-of-m]
    SPLIT -->|No| SINGLE[Backup singolo]
    SHAMIR --> DIST[Distribuire]
    SINGLE --> STORE[Salvare]
    DIST --> LOC1[Sede 1]
    DIST --> LOC2[Sede 2]
    DIST --> LOC3[Sede 3]
    STORE --> OFFSITE[Offsite Storage]
    LOC1 --> VERIFY[Test Restore]
    LOC2 --> VERIFY
    LOC3 --> VERIFY
    OFFSITE --> VERIFY

    style ENCRYPT fill:#fff3e0
    style VERIFY fill:#e8f5e9
</mermaid>

----

===== Esempio codice: Backup crittografato =====

<code csharp>
using WvdS.Security.Cryptography.X509Certificates.Extensions.PQ;
using System.Security.Cryptography;

public class KeyBackupService
{
    public void CreateEncryptedBackup(
        AsymmetricAlgorithm privateKey,
        string backupPath,
        string backupPassword,
        BackupOptions options = null)
    {
        options ??= BackupOptions.Default;
        using var ctx = PqCryptoContext.Initialize();

        // 1. Esportare chiave privata come PKCS#8
        byte[] pkcs8 = privateKey switch
        {
            RSA rsa => rsa.ExportPkcs8PrivateKey(),
            ECDsa ecdsa => ecdsa.ExportPkcs8PrivateKey(),
            _ => ctx.ExportPrivateKey(privateKey)
        };

        // 2. Derivare Key Encryption Key (KEK)
        var salt = RandomNumberGenerator.GetBytes(32);
        var kek = ctx.DeriveKey(
            backupPassword,
            salt,
            outputLength: 32,
            algorithm: KeyDerivationAlgorithm.Argon2id,
            iterations: 4,
            memoryKiB: 65536,
            parallelism: 4
        );

        // 3. Crittografare con AES-256-GCM
        var nonce = RandomNumberGenerator.GetBytes(12);
        var ciphertext = new byte[pkcs8.Length];
        var tag = new byte[16];

        using var aes = new OpenSslAesGcm(kek);
        aes.Encrypt(nonce, pkcs8, ciphertext, tag);

        // 4. Creare file backup
        var backup = new KeyBackup
        {
            Version = 1,
            Algorithm = "ML-DSA-65",
            CreatedAt = DateTime.UtcNow,
            KdfAlgorithm = "Argon2id",
            KdfSalt = Convert.ToBase64String(salt),
            KdfIterations = 4,
            KdfMemoryKiB = 65536,
            EncryptionAlgorithm = "AES-256-GCM",
            Nonce = Convert.ToBase64String(nonce),
            Tag = Convert.ToBase64String(tag),
            EncryptedKey = Convert.ToBase64String(ciphertext),
            Checksum = ComputeChecksum(pkcs8)
        };

        // 5. Salvare come JSON
        var json = JsonSerializer.Serialize(backup, new JsonSerializerOptions
        {
            WriteIndented = true
        });
        File.WriteAllText(backupPath, json);

        // 6. Pulire memoria
        CryptographicOperations.ZeroMemory(pkcs8);
        CryptographicOperations.ZeroMemory(kek);

        Console.WriteLine($"Backup creato: {backupPath}");
        Console.WriteLine($"  Checksum: {backup.Checksum}");
    }

    public AsymmetricAlgorithm RestoreFromBackup(
        string backupPath,
        string backupPassword)
    {
        using var ctx = PqCryptoContext.Initialize();

        // 1. Caricare backup
        var json = File.ReadAllText(backupPath);
        var backup = JsonSerializer.Deserialize<KeyBackup>(json);

        // 2. Derivare KEK (stessi parametri del backup)
        var salt = Convert.FromBase64String(backup.KdfSalt);
        var kek = ctx.DeriveKey(
            backupPassword,
            salt,
            outputLength: 32,
            algorithm: KeyDerivationAlgorithm.Argon2id,
            iterations: backup.KdfIterations,
            memoryKiB: backup.KdfMemoryKiB,
            parallelism: 4
        );

        // 3. Decrittografare
        var nonce = Convert.FromBase64String(backup.Nonce);
        var tag = Convert.FromBase64String(backup.Tag);
        var ciphertext = Convert.FromBase64String(backup.EncryptedKey);
        var pkcs8 = new byte[ciphertext.Length];

        using var aes = new OpenSslAesGcm(kek);
        aes.Decrypt(nonce, ciphertext, tag, pkcs8);

        // 4. Verificare checksum
        var checksum = ComputeChecksum(pkcs8);
        if (checksum != backup.Checksum)
        {
            throw new CryptographicException("Checksum backup non valido");
        }

        // 5. Importare chiave
        var key = ctx.ImportPrivateKey(pkcs8, backup.Algorithm);

        CryptographicOperations.ZeroMemory(pkcs8);
        CryptographicOperations.ZeroMemory(kek);

        Console.WriteLine($"Backup ripristinato: {backup.Algorithm}");
        return key;
    }

    private string ComputeChecksum(byte[] data)
    {
        var hash = SHA256.HashData(data);
        return Convert.ToHexString(hash).Substring(0, 16);
    }
}

public class KeyBackup
{
    public int Version { get; set; }
    public string Algorithm { get; set; }
    public DateTime CreatedAt { get; set; }
    public string KdfAlgorithm { get; set; }
    public string KdfSalt { get; set; }
    public int KdfIterations { get; set; }
    public int KdfMemoryKiB { get; set; }
    public string EncryptionAlgorithm { get; set; }
    public string Nonce { get; set; }
    public string Tag { get; set; }
    public string EncryptedKey { get; set; }
    public string Checksum { get; set; }
}
</code>

----

===== Esempio codice: Shamir Secret Sharing =====

<code csharp>
using SecretSharingDotNet.Cryptography;

public class ShamirKeyBackup
{
    public ShamirShares SplitKey(
        byte[] privateKey,
        int totalShares,
        int threshold)
    {
        // Shamir's Secret Sharing: schema n-of-m
        // es. 3-of-5: necessari almeno 3 di 5 share

        var gf = new ExtendedEuclideanAlgorithm<BigInteger>();
        var shamir = new ShamirsSecretSharing<BigInteger>(gf);

        // Chiave come BigInteger
        var secret = new BigInteger(privateKey, isUnsigned: true);

        // Dividere in share
        var shares = shamir.MakeShares(
            (uint)threshold,
            (uint)totalShares,
            secret
        );

        var result = new ShamirShares
        {
            Threshold = threshold,
            TotalShares = totalShares,
            Shares = shares.Select((s, i) => new Share
            {
                Index = i + 1,
                Value = Convert.ToBase64String(s.Y.ToByteArray())
            }).ToList()
        };

        Console.WriteLine($"Chiave divisa in {totalShares} share (Threshold: {threshold})");
        return result;
    }

    public byte[] RecombineKey(ShamirShares shares, List<int> shareIndices)
    {
        if (shareIndices.Count < shares.Threshold)
        {
            throw new ArgumentException(
                $"Necessari almeno {shares.Threshold} share, ma presenti solo {shareIndices.Count}"
            );
        }

        var gf = new ExtendedEuclideanAlgorithm<BigInteger>();
        var shamir = new ShamirsSecretSharing<BigInteger>(gf);

        // Raccogliere share
        var selectedShares = shareIndices
            .Select(i => shares.Shares.First(s => s.Index == i))
            .Select(s => new FinitePoint<BigInteger>(
                s.Index,
                new BigInteger(Convert.FromBase64String(s.Value), isUnsigned: true)
            ))
            .ToArray();

        // Ricostruire segreto
        var secret = shamir.Reconstruction(selectedShares);

        return secret.ToByteArray();
    }

    public void DistributeShares(ShamirShares shares, string[] recipients)
    {
        // Distribuire share a diverse persone/sedi
        for (int i = 0; i < shares.Shares.Count && i < recipients.Length; i++)
        {
            var share = shares.Shares[i];
            var recipient = recipients[i];

            // In pratica: inviare crittografato al destinatario
            Console.WriteLine($"Share {share.Index} → {recipient}");

            // Esempio: come codice QR o chiavetta USB
            var shareFile = $"share-{share.Index}-{recipient.Replace(" ", "_")}.json";
            File.WriteAllText(shareFile, JsonSerializer.Serialize(share));
        }
    }
}

public class ShamirShares
{
    public int Threshold { get; set; }
    public int TotalShares { get; set; }
    public List<Share> Shares { get; set; }
}

public class Share
{
    public int Index { get; set; }
    public string Value { get; set; }
}
</code>

----

===== Strategia di backup per tipo di chiave =====

^  Tipo chiave  ^  Metodo backup  ^  Copie  ^  Sedi  ^  Conservazione  ^
| **Root-CA** | Shamir 3-of-5 + HSM | 5 | 3 geo-distribuite | Permanente |
| **Intermediate-CA** | Encrypted + HSM | 3 | 2 sedi | 10 anni |
| **TLS Server** | Encrypted | 2 | Datacenter + Offsite | 2 anni |
| **Code Signing** | Shamir 2-of-3 | 3 | 2 sedi | 5 anni |
| **User Keys** | Encrypted | 2 | Locale + Cloud | 1 anno |

----

===== Requisiti di backup specifici per settore =====

^  Settore  ^  Requisito  ^  Metodo  ^  Particolarità  ^
| **Finanza** | PCI-DSS | HSM + Dual Control | Obbligo Audit-Log |
| **Sanità** | HIPAA | Key Escrow | Accesso per emergenze |
| **Enti pubblici** | VS-NfD | Cassaforte + 2 persone | Responsabile protezione segreti |
| **Energia** | KRITIS | Backup offline | Sistema air-gapped |

----

===== Scenari correlati =====

^  Relazione  ^  Scenario  ^  Descrizione  ^
| **Prerequisito** | [[.:speicherung|11.2 Archiviazione chiavi]] | Conservare chiavi in sicurezza |
| **Correlato** | [[.:rotation|11.3 Rotazione chiavi]] | Backup prima della rotazione |
| **Passo successivo** | [[.:vernichtung|11.5 Distruzione chiavi]] | Eliminare backup vecchi |
| **Correlato** | [[it:int:pqcrypt:szenarien:verwaltung:backup|4.4 Backup certificati]] | Backup certificati |

----

<< [[.:rotation|11.3 Rotazione chiavi]] | [[.:start|Panoramica chiavi]] | [[.:vernichtung|11.5 Distruzione chiavi]] >>

{{tag>scenario chiave backup shamir disaster-recovery hsm}}

----
//Wolfgang van der Stille @ EMSR DATA d.o.o. - Post-Quantum Cryptography Professional//