Agent Skills: Azure.Security.KeyVault.Keys (.NET)

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

| Type | Purpose | |------|---------| | KeyClient | Key management operations | | CryptographyClient | Cryptographic operations | | KeyResolver | Resolve key ID to CryptographyClient | | KeyVaultKey | Key with cryptographic material | | KeyProperties | Key metadata (no crypto material) | | CreateRsaKeyOptions | RSA key creation options | | CreateEcKeyOptions | EC key creation options | | CreateOctKeyOptions | Symmetric key options | | EncryptResult | Encryption result | | DecryptResult | Decryption result | | SignResult | Signing result | | VerifyResult | Verification result | | WrapResult | Key wrap result | | UnwrapResult | Key unwrap result |

Algorithms Reference

Encryption Algorithms

| Algorithm | Key Type | Description | |-----------|----------|-------------| | RsaOaep | RSA | RSA-OAEP | | RsaOaep256 | RSA | RSA-OAEP-256 | | Rsa15 | RSA | RSA 1.5 (legacy) | | A128Gcm | Oct | AES-128-GCM | | A256Gcm | Oct | AES-256-GCM |

Signature Algorithms

| Algorithm | Key Type | Description | |-----------|----------|-------------| | RS256 | RSA | RSASSA-PKCS1-v1_5 SHA-256 | | RS384 | RSA | RSASSA-PKCS1-v1_5 SHA-384 | | RS512 | RSA | RSASSA-PKCS1-v1_5 SHA-512 | | PS256 | RSA | RSASSA-PSS SHA-256 | | ES256 | EC | ECDSA P-256 SHA-256 | | ES384 | EC | ECDSA P-384 SHA-384 | | ES512 | EC | ECDSA P-521 SHA-512 |

Key Wrap Algorithms

| Algorithm | Key Type | Description | |-----------|----------|-------------| | RsaOaep | RSA | RSA-OAEP | | RsaOaep256 | RSA | RSA-OAEP-256 | | A128KW | Oct | AES-128 Key Wrap | | A256KW | Oct | AES-256 Key Wrap |

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

| Role | Permissions | |------|-------------| | Key Vault Crypto Officer | Full key management | | Key Vault Crypto User | Use keys for crypto operations | | Key Vault Reader | Read key metadata |

Related SDKs

| SDK | Purpose | Install | |-----|---------|---------| | Azure.Security.KeyVault.Keys | Keys (this SDK) | dotnet add package Azure.Security.KeyVault.Keys | | Azure.Security.KeyVault.Secrets | Secrets | dotnet add package Azure.Security.KeyVault.Secrets | | Azure.Security.KeyVault.Certificates | Certificates | dotnet add package Azure.Security.KeyVault.Certificates | | Azure.Identity | Authentication | dotnet add package Azure.Identity |

Reference Links

| Resource | URL | |----------|-----| | NuGet Package | https://www.nuget.org/packages/Azure.Security.KeyVault.Keys | | API Reference | https://learn.microsoft.com/dotnet/api/azure.security.keyvault.keys | | Quickstart | https://learn.microsoft.com/azure/key-vault/keys/quick-create-net | | GitHub Source | https://github.com/Azure/azure-sdk-for-net/tree/main/sdk/keyvault/Azure.Security.KeyVault.Keys |