AESDECRYPT

AESDECRYPT

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Action

This statement of function uses the Xmega AES encryption engine to decrypt a block of data.

 

 

Syntax

AESDECRYPT  key, var , size

targ = AESDECRYPT ( key, var , size)

 

 

Remarks

key

The name of a label that contains 16 bytes of key data. Or an array holding 16 bytes of key data.

var

A variable or array containing the data to be encrypted. When you use the statement, this variable will contain the encrypted data after the conversion.

size

The number of bytes to encrypt. Encryption is done with blocks of 16 bytes. So the size should be a multiple of 16. If you supply only 14 bytes this is ok too, but the result will still be 16 bytes.

noticeIt is important that your array is big enough to hold the result.

Without the full 16 byte result, you can not decrypt the data.

targ

In case you use the function, this variable will hold the result.

 

This function only works for Xmega chips that have an AES encryption unit.

128 bit encryption is used.

 

You can either use a label with a fixed key, or use a variable.

You should use the same key data for encryption and decryption.

 

 

 

See also

AESENCRYPT , $AESKEY

 

 

Example

'----------------------------------------------------------------
'                  (c) 1995-2016 MCS
'                      xm128-AES.bas
'  This sample demonstrates the Xmega128A1 AES encryption/decryption
'-----------------------------------------------------------------
 
$regfile = "xm128a1def.dat"
$crystal = 32000000
$hwstack = 64
$swstack = 40
$framesize = 40
 
 
'first enable the osc of your choice
Config Osc = Enabled , 32mhzosc = Enabled
 
'configure the systemclock
Config Sysclock = 32mhz , Prescalea = 1 , Prescalebc = 1_1
 
Config Com1 = 38400 , Mode = Asynchroneous , Parity = None , Stopbits = 1 , Databits = 8
 
'$external _aes_enc
 
Dim Key(16) As Byte                                         ' room for key
Dim Ar(34) As Byte
Dim Arenc(34) As Byte
Dim J As Byte
Print "AES test"
 
Restore Keydata
For J = 1 To 16                                             ' load a key to memory
  Read Key(j)
Next
 
'load some data
For J = 1 To 32                                             ' fill some data to encrypt
 Ar(j) = J
Next
 
 
Aesencrypt Keydata , Ar(1) , 32
Print "Encrypted data"
For J = 1 To 32                                             ' fill some data to encrypt
Print Ar(j)
Next
 
 
Aesdecrypt Keydata , Ar(1) , 32
Print "Decrypted data"
For J = 1 To 32                                             ' fill some data to encrypt
Print Ar(j)
Next
 
Print "Encrypt function"
Arenc(1) = Aesencrypt(keydata , Ar(1) , 32)
For J = 1 To 32                                             ' fill some data to encrypt
Print Ar(j) ; "-" ; Arenc(j)
Next
 
Print "Decrypt function"
Ar(1) = Aesdecrypt(keydata , Arenc(1) , 32)
 
For J = 1 To 32
Print J ; ">" ; Ar(j) ; "-" ; Arenc(j)
Next
 
End
 
 
 
Keydata:
Data 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16