A Factory class that returns CALG (Confidentiality Algorithm) instances
that operate as described in the draft-burdis-cat-sasl-srp-08.
The designated CALG block cipher should be used in OFB (Output Feedback
Block) mode in the ISO variant, as described in
The Handbook of Applied
Cryptography, algorithm 7.20.
Let
k
be the block size of the chosen symmetric key block
cipher algorithm; e.g. for AES this is
128
bits or
16
octets. The OFB mode used shall be of length/size
k
.
It is recommended that block ciphers operating in OFB mode be used with an
Initial Vector (the mode's IV). In such a mode of operation - OFB with key
re-use - the IV need not be secret. For the mechanism in question the IVs
shall be a random octet sequence of
k
bytes.
The input data to the confidentiality protection algorithm shall be
a multiple of the symmetric cipher block size
k
. When the input
length is not a multiple of
k
octets, the data shall be padded
according to the following scheme:
Assuming the length of the input is
l
octets,
(k - (l mod k))
octets, all having the value
(k - (l mod k))
, shall be appended to the original data. In
other words, the input is padded at the trailing end with one of the
following sequences:
01 -- if l mod k = k-1
02 02 -- if l mod k = k-2
...
...
...
k k ... k k -- if l mod k = 0
The padding can be removed unambiguously since all input is padded and no
padding sequence is a suffix of another. This padding method is well-defined
if and only if
k < 256
octets, which is the case with
symmetric key block ciphers today, and in the forseeable future.
doFinal
public byte[] doFinal(byte[] data)
throws ConfidentialityException
Encrypts or decrypts, depending on the mode already set, a designated
array of bytes and returns the result.
data
- the data to encrypt/decrypt.
- the decrypted/encrypted result.
doFinal
public byte[] doFinal(byte[] data,
int offset,
int length)
throws ConfidentialityException
Encrypts or decrypts, depending on the mode already set, a designated
array of bytes and returns the result.
data
- the data to encrypt/decrypt.offset
- where to start in data
.length
- how many bytes to consider in data
.
- the decrypted/encrypted result.
getInstance
(package private) static CALG getInstance(String algorithm)
Returns an instance of a SASL-SRP CALG implementation.
algorithm
- the name of the symmetric cipher algorithm.
- an instance of this object.
init
public void init(KDF kdf,
byte[] iv,
Direction dir)
throws SaslException
Initialises a SASL-SRP CALG implementation.
kdf
- the key derivation function.iv
- the initial vector value to use.dir
- whether this CALG is used for encryption or decryption.