**javacard.security** 
 ====Interface HMACKey  ====

**All Superinterfaces:** [[javacard:java-card-api:Key|Key]] , [[javacard:java-card-api:SecretKey|SecretKey]]  
 



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  *[[javacard:java-card-api:secretkey|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 bits for SHA-1)
 When the key data is set, the key is initialized and ready for use.





**Since:**
  2.2.2 
 

**See Also:**[[javacard:java-card-api:KeyBuilder|KeyBuilder]] , 
[[javacard:java-card-api:Signature|Signature]] , 
[[javacard:java-card-api:Cipher|javacardx.crypto.Cipher]] , 
[[javacard:java-card-api:KeyEncryption|javacardx.crypto.KeyEncryption]]  
 


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^ Method Summary ^^ 
| ** byte** | **[[javacard:java-card-api:HMACKey#getKey(byte[], short)|getKey]] **(byte[] keyData,short kOff)          Returns the Key data in plain text. |
| ** void** | **[[javacard:java-card-api:HMACKey#setKey(byte[], short, short)|setKey]] **(byte[] keyData,short kOff,short kLen)          Sets the Key data. |

 

^ Methods inherited from interface javacard.security.Key ^ 
| [[javacard:java-card-api:Key#clearKey()|clearKey]] , [[javacard:java-card-api:Key#getSize()|getSize]] , [[javacard:java-card-api:Key#getType()|getType]] , [[javacard:java-card-api:Key#isInitialized()|isInitialized]]  |

 






^ Method Detail ^ 



 === setKey === 
void **setKey**(byte[] keyData,
short kOff,
short kLen)
throws [[javacard:java-card-api:CryptoException|CryptoException]] ,
[[javacard:java-card-api:NullPointerException|NullPointerException]] ,
[[javacard:java-card-api:ArrayIndexOutOfBoundsException|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:**
[[javacard:java-card-api:CryptoException|CryptoException]]  - with the following reason code:
 \\ 
 
  *CryptoException.ILLEGAL_VALUE if input data decryption is required and fails.
 \\  
 
 
[[javacard:java-card-api:ArrayIndexOutOfBoundsException|ArrayIndexOutOfBoundsException]]  - if kOff is negative
 or the keyData array is too short
 
 
[[javacard:java-card-api:NullPointerException|NullPointerException]]  - if the keyData parameter is null 
 

 
 



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 === 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).

 
 


 
 


**Parameters:**keyData - byte array to return key data 
 
kOff - offset within keyData to start
 
 
**Returns:**the byte length of the key data returned
 
 
**Throws:**
[[javacard:java-card-api:CryptoException|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:**[[javacard:java-card-api:Key|Key]]