**javacard.security** 
 ====Interface RSAPrivateKey  ====

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



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  *[[javacard:java-card-api:privatekey|PrivateKey]] \\ 




The RSAPrivateKey class is used to sign data using the RSA algorithm
 in its modulus/exponent form. It may also be used by the javacardx.crypto.Cipher class
 to encrypt/decrypt messages.
 When both the modulus and exponent of the key are set, the key is
 initialized and ready for use.




**See Also:**[[javacard:java-card-api:RSAPublicKey|RSAPublicKey]] , 
[[javacard:java-card-api:RSAPrivateCrtKey|RSAPrivateCrtKey]] , 
[[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 ^^ 
| ** short** | **[[javacard:java-card-api:RSAPrivateKey#getExponent(byte[], short)|getExponent]] **(byte[] buffer,short offset)          Returns the private exponent value of the key in plain text. |
| ** short** | **[[javacard:java-card-api:RSAPrivateKey#getModulus(byte[], short)|getModulus]] **(byte[] buffer,short offset)          Returns the modulus value of the key in plain text. |
| ** void** | **[[javacard:java-card-api:RSAPrivateKey#setExponent(byte[], short, short)|setExponent]] **(byte[] buffer,short offset,short length)          Sets the private exponent value of the key. |
| ** void** | **[[javacard:java-card-api:RSAPrivateKey#setModulus(byte[], short, short)|setModulus]] **(byte[] buffer,short offset,short length)          Sets the modulus value of the key. |

 

^ 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 ^ 



 === setModulus === 
void **setModulus**(byte[] buffer,
short offset,
short length)
throws [[javacard:java-card-api:CryptoException|CryptoException]] 

Sets the modulus value of the key.
 The plain text data format is big-endian and right-aligned (the least significant bit is the least significant
 bit of last byte). Input modulus 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//, the modulus value is decrypted using the //Cipher// object.// 
 \\  

 
 


 
 


**Parameters:**buffer - the input buffer 
 
offset - the offset into the input buffer at which the modulus value begins 
 
length - the length of the modulus
 
 
**Throws:**
[[javacard:java-card-api:CryptoException|CryptoException]]  - with the following reason code:
 \\ 
 
  *CryptoException.ILLEGAL_VALUE if the input modulus data length is inconsistent with the implementation or if input data decryption is required and fails. 
 \\   
 

 
 



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 === setExponent === 
void **setExponent**(byte[] buffer,
short offset,
short length)
throws [[javacard:java-card-api:CryptoException|CryptoException]] 

Sets the private exponent value of the key.
 The plain text data format is big-endian and right-aligned (the least significant bit is the least significant
 bit of last byte). Input exponent 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//, the exponent value is decrypted using the //Cipher// object.// 
 \\  

 
 


 
 


**Parameters:**buffer - the input buffer 
 
offset - the offset into the input buffer at which the exponent value begins 
 
length - the length of the exponent
 
 
**Throws:**
[[javacard:java-card-api:CryptoException|CryptoException]]  - with the following reason code:
 \\ 
 
  *CryptoException.ILLEGAL_VALUE if the input exponent data length is inconsistent with the implementation or if input data decryption is required and fails. 
 \\   
 

 
 



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 === getModulus === 
short **getModulus**(byte[] buffer,
short offset)

Returns the modulus value of the key in plain text.
 The data format is big-endian and right-aligned (the least significant bit is the least significant
 bit of last byte).

 
 


 
 


**Parameters:**buffer - the output buffer 
 
offset - the offset into the output buffer at which the modulus value starts
 
 
**Returns:**the byte length of the modulus value returned
 
 
**Throws:**
[[javacard:java-card-api:CryptoException|CryptoException]]  - with the following reason code:
 \\ 
 
  *CryptoException.UNINITIALIZED_KEY if the modulus value of the key 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]]  
 

 
 



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 === getExponent === 
short **getExponent**(byte[] buffer,
short offset)

Returns the private exponent value of the key in plain text.
 The data format is big-endian and right-aligned (the least significant bit is the least significant
 bit of last byte).

 
 


 
 


**Parameters:**buffer - the output buffer 
 
offset - the offset into the output buffer at which the exponent value begins
 
 
**Returns:**the byte length of the private exponent value returned
 
 
**Throws:**
[[javacard:java-card-api:CryptoException|CryptoException]]  - with the following reason code:
 \\ 
 
  *CryptoException.UNINITIALIZED_KEY if the private exponent value of the key 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]]