Microsoft Azure Security Keyvault Keys Dotnet

Azure.Security.KeyVault.Keys (.NET)

Client library for managing cryptographic keys in Azure Key Vault and Managed HSM.

Installation

dotnet add package Azure.Security.KeyVault.Keys
dotnet add package Azure.Identity

Current Version: 4.7.0 (stable)

Environment Variables

KEY_VAULT_NAME=<your-key-vault-name>  # Required: Key Vault name
AZURE_KEYVAULT_URL=https://<vault-name>.vault.azure.net  # Optional: full Key Vault URL
AZURE_TOKEN_CREDENTIALS=prod  # Required only if DefaultAzureCredential is used in production

Client Hierarchy

KeyClient (key management)
├── CreateKey / CreateRsaKey / CreateEcKey
├── GetKey / GetKeys
├── UpdateKeyProperties
├── DeleteKey / PurgeDeletedKey
├── BackupKey / RestoreKey
└── GetCryptographyClient() → CryptographyClient

CryptographyClient (cryptographic operations)
├── Encrypt / Decrypt
├── WrapKey / UnwrapKey
├── Sign / Verify
└── SignData / VerifyData

KeyResolver (key resolution)
└── Resolve(keyId) → CryptographyClient

Authentication

Microsoft Entra Token Credential

using Azure.Identity;
using Azure.Security.KeyVault.Keys;

var keyVaultName = Environment.GetEnvironmentVariable("KEY_VAULT_NAME");
var kvUri = $"https://{keyVaultName}.vault.azure.net";

// Local dev: DefaultAzureCredential. Production: set AZURE_TOKEN_CREDENTIALS=prod or AZURE_TOKEN_CREDENTIALS=<specific_credential>
var credential = new DefaultAzureCredential(
    DefaultAzureCredential.DefaultEnvironmentVariableName
);
// Or use a specific credential directly in production:
// See https://learn.microsoft.com/dotnet/api/overview/azure/identity-readme?view=azure-dotnet#credential-classes
// var credential = new ManagedIdentityCredential();
var client = new KeyClient(new Uri(kvUri), credential);

Service Principal

var credential = new ClientSecretCredential(
    tenantId: "<tenant-id>",
    clientId: "<client-id>",
    clientSecret: "<client-secret>");

var client = new KeyClient(new Uri(kvUri), credential);

Key Management

Create Keys

// Create RSA key
KeyVaultKey rsaKey = await client.CreateKeyAsync("my-rsa-key", KeyType.Rsa);
Console.WriteLine($"Created key: {rsaKey.Name}, Type: {rsaKey.KeyType}");

// Create RSA key with options
var rsaOptions = new CreateRsaKeyOptions("my-rsa-key-2048")
{
    KeySize = 2048,
    HardwareProtected = false, // true for HSM-backed
    ExpiresOn = DateTimeOffset.UtcNow.AddYears(1),
    NotBefore = DateTimeOffset.UtcNow,
    Enabled = true
};
rsaOptions.KeyOperations.Add(KeyOperation.Encrypt);
rsaOptions.KeyOperations.Add(KeyOperation.Decrypt);

KeyVaultKey rsaKey2 = await client.CreateRsaKeyAsync(rsaOptions);

// Create EC key
var ecOptions = new CreateEcKeyOptions("my-ec-key")
{
    CurveName = KeyCurveName.P256,
    HardwareProtected = true // HSM-backed
};
KeyVaultKey ecKey = await client.CreateEcKeyAsync(ecOptions);

// Create Oct (symmetric) key for wrap/unwrap
var octOptions = new CreateOctKeyOptions("my-oct-key")
{
    KeySize = 256,
    HardwareProtected = true
};
KeyVaultKey octKey = await client.CreateOctKeyAsync(octOptions);

Retrieve Keys

// Get specific key (latest version)
KeyVaultKey key = await client.GetKeyAsync("my-rsa-key");
Console.WriteLine($"Key ID: {key.Id}");
Console.WriteLine($"Key Type: {key.KeyType}");
Console.WriteLine($"Version: {key.Properties.Version}");

// Get specific version
KeyVaultKey keyVersion = await client.GetKeyAsync("my-rsa-key", "version-id");

// List all keys
await foreach (KeyProperties keyProps in client.GetPropertiesOfKeysAsync())
{
    Console.WriteLine($"Key: {keyProps.Name}, Enabled: {keyProps.Enabled}");
}

// List key versions
await foreach (KeyProperties version in client.GetPropertiesOfKeyVersionsAsync("my-rsa-key"))
{
    Console.WriteLine($"Version: {version.Version}, Created: {version.CreatedOn}");
}

Update Key Properties

KeyVaultKey key = await client.GetKeyAsync("my-rsa-key");

key.Properties.ExpiresOn = DateTimeOffset.UtcNow.AddYears(2);
key.Properties.Tags["environment"] = "production";

KeyVaultKey updatedKey = await client.UpdateKeyPropertiesAsync(key.Properties);

Delete and Purge Keys

// Start delete operation
DeleteKeyOperation operation = await client.StartDeleteKeyAsync("my-rsa-key");

// Wait for deletion to complete (required before purge)
await operation.WaitForCompletionAsync();
Console.WriteLine($"Deleted key scheduled purge date: {operation.Value.ScheduledPurgeDate}");

// Purge immediately (if soft-delete is enabled)
await client.PurgeDeletedKeyAsync("my-rsa-key");

// Or recover deleted key
KeyVaultKey recoveredKey = await client.StartRecoverDeletedKeyAsync("my-rsa-key");

Backup and Restore

// Backup key
byte[] backup = await client.BackupKeyAsync("my-rsa-key");
await File.WriteAllBytesAsync("key-backup.bin", backup);

// Restore key
byte[] backupData = await File.ReadAllBytesAsync("key-backup.bin");
KeyVaultKey restoredKey = await client.RestoreKeyBackupAsync(backupData);

Cryptographic Operations

Get CryptographyClient

// From KeyClient
KeyVaultKey key = await client.GetKeyAsync("my-rsa-key");
CryptographyClient cryptoClient = client.GetCryptographyClient(
    key.Name, 
    key.Properties.Version);

// Or create directly with key ID
CryptographyClient cryptoClient = new CryptographyClient(
    new Uri("https://myvault.vault.azure.net/keys/my-rsa-key/version"),
    new DefaultAzureCredential());

Encrypt and Decrypt

byte[] plaintext = Encoding.UTF8.GetBytes("Secret message to encrypt");

// Encrypt
EncryptResult encryptResult = await cryptoClient.EncryptAsync(
    EncryptionAlgorithm.RsaOaep256, 
    plaintext);
Console.WriteLine($"Encrypted: {Convert.ToBase64String(encryptResult.Ciphertext)}");

// Decrypt
DecryptResult decryptResult = await cryptoClient.DecryptAsync(
    EncryptionAlgorithm.RsaOaep256, 
    encryptResult.Ciphertext);
string decrypted = Encoding.UTF8.GetString(decryptResult.Plaintext);
Console.WriteLine($"Decrypted: {decrypted}");

Wrap and Unwrap Keys

// Key to wrap (e.g., AES key)
byte[] keyToWrap = new byte[32]; // 256-bit key
RandomNumberGenerator.Fill(keyToWrap);

// Wrap key
WrapResult wrapResult = await cryptoClient.WrapKeyAsync(
    KeyWrapAlgorithm.RsaOaep256, 
    keyToWrap);

// Unwrap key
UnwrapResult unwrapResult = await cryptoClient.UnwrapKeyAsync(
    KeyWrapAlgorithm.RsaOaep256, 
    wrapResult.EncryptedKey);

Sign and Verify

// Data to sign
byte[] data = Encoding.UTF8.GetBytes("Data to sign");

// Sign data (computes hash internally)
SignResult signResult = await cryptoClient.SignDataAsync(
    SignatureAlgorithm.RS256, 
    data);

// Verify signature
VerifyResult verifyResult = await cryptoClient.VerifyDataAsync(
    SignatureAlgorithm.RS256, 
    data, 
    signResult.Signature);
Console.WriteLine($"Signature valid: {verifyResult.IsValid}");

// Or sign pre-computed hash
using var sha256 = SHA256.Create();
byte[] hash = sha256.ComputeHash(data);

SignResult signHashResult = await cryptoClient.SignAsync(
    SignatureAlgorithm.RS256, 
    hash);

Key Resolver

using Azure.Security.KeyVault.Keys.Cryptography;

var resolver = new KeyResolver(new DefaultAzureCredential());

// Resolve key by ID to get CryptographyClient
CryptographyClient cryptoClient = await resolver.ResolveAsync(
    new Uri("https://myvault.vault.azure.net/keys/my-key/version"));

// Use for encryption
EncryptResult result = await cryptoClient.EncryptAsync(
    EncryptionAlgorithm.RsaOaep256, 
    plaintext);

Key Rotation

// Rotate key (creates new version)
KeyVaultKey rotatedKey = await client.RotateKeyAsync("my-rsa-key");
Console.WriteLine($"New version: {rotatedKey.Properties.Version}");

// Get rotation policy
KeyRotationPolicy policy = await client.GetKeyRotationPolicyAsync("my-rsa-key");

// Update rotation policy
policy.ExpiresIn = "P90D"; // 90 days
policy.LifetimeActions.Add(new KeyRotationLifetimeAction
{
    Action = KeyRotationPolicyAction.Rotate,
    TimeBeforeExpiry = "P30D" // Rotate 30 days before expiry
});

await client.UpdateKeyRotationPolicyAsync("my-rsa-key", policy);

Key Types Reference

Algorithms Reference

Encryption Algorithms

Signature Algorithms

Key Wrap Algorithms

Best Practices

1. Use Managed Identity — Prefer DefaultAzureCredential over secrets
2. Enable soft-delete — Protect against accidental deletion
3. Use HSM-backed keys — Set HardwareProtected = true for sensitive keys
4. Implement key rotation — Use automatic rotation policies
5. Limit key operations — Only enable required KeyOperations
6. Set expiration dates — Always set ExpiresOn for keys
7. Use specific versions — Pin to versions in production
8. Cache CryptographyClient — Reuse for multiple operations

Error Handling

using Azure;

try
{
    KeyVaultKey key = await client.GetKeyAsync("my-key");
}
catch (RequestFailedException ex) when (ex.Status == 404)
{
    Console.WriteLine("Key not found");
}
catch (RequestFailedException ex) when (ex.Status == 403)
{
    Console.WriteLine("Access denied - check RBAC permissions");
}
catch (RequestFailedException ex)
{
    Console.WriteLine($"Key Vault error: {ex.Status} - {ex.Message}");
}

Required RBAC Roles

Related SDKs

Reference Links