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## javacard.security
Interface HMACKey

All Superinterfaces:
  Key, SecretKey

    @TransactionType(value=SUPPORTS)
    public interface HMACKey

extends SecretKey

`HMACKey` contains a key for HMAC operations. This key can be of any length, but it is strongly recommended that the key is not shorter than the byte length of the hash output used in the HMAC implementation. Keys with length greater than the hash block length are first hashed with the hash algorithm used for the HMAC implementation.

Implementations must support an HMAC key length equal to the length of the supported hash algorithm block size (e.g 64 bytes for SHA-1)

When the key data is set, the key is initialized and ready for use.

Since:
  2.2.2
See Also:
  `KeyBuilder`, `Signature`, `javacardx.crypto.Cipher`, `javacardx.crypto.KeyEncryption`

Method Summary
`byte` | `getKey(byte[] keyData, short kOff)` Returns the `Key` data in plain text.
`void` | `setKey(byte[] keyData, short kOff, short kLen)` Sets the `Key` data.

Methods inherited from interface javacard.security.Key
`clearKey, getSize, getType, getTypeName, isInitialized`

Method Detail

### setKey

    void setKey(byte[] keyData,
                short kOff,
                short kLen)
                throws CryptoException,
                       NullPointerException,
                       ArrayIndexOutOfBoundsException

  Sets the `Key` data. The data format is big-endian and right-aligned (the least significant bit is the least significant bit of last byte). Input key data is copied into the internal representation.

  Note:

  - If the key object implements the `javacardx.crypto.KeyEncryption` interface and the `Cipher` object specified via `setKeyCipher()` is not `null`, `keyData` is decrypted using the `Cipher` object.

  Parameters:
    `keyData` - byte array containing key initialization data
    `kOff` - offset within keyData to start
    `kLen` - the byte length of the key initialization data
  Throws:
    `CryptoException` - with the following reason code:
    - `CryptoException.ILLEGAL_VALUE` if the `kLen` parameter is 0 or invalid or if the `keyData` parameter is inconsistent with the key length or if input data decryption is required and fails.
    `ArrayIndexOutOfBoundsException` - if `kOff` is negative or the `keyData` array is too short
    `NullPointerException` - if the `keyData` parameter is `null`

### getKey

    byte getKey(byte[] keyData,
                short kOff)

  Returns the `Key` data in plain text. The key can be any length, but should be longer than the byte length of the hash algorithm output used. The data format is big-endian and right-aligned (the least significant bit is the least significant bit of last byte).

  Note:

  - If the byte length of the key data exceeds 127, this method returns -1. The data is nevertheless placed in the `keyData` buffer if it fits. Please use the `getSize()` method to obtain the actual key length in bits.

  Parameters:
    `keyData` - byte array to return key data
    `kOff` - offset within `keyData` to start
  Returns:
    the byte length of the key data returned
  Throws:
    `CryptoException` - with the following reason code:
    - `CryptoException.UNINITIALIZED_KEY` if the key data has not been successfully initialized since the time the initialized state of the key was set to false.
  See Also:
    `Key`

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