public class UMac32 extends BaseMac
The implementation of the UMAC (Universal Message Authentication Code).
The UMAC algorithms described are parameterized. This means that various low-level choices, like the endian convention and the underlying cryptographic primitive, have not been fixed. One must choose values for these parameters before the authentication tag generated by UMAC (for a given message, key, and nonce) becomes fully-defined. In this document we provide two collections of parameter settings, and have named the sets UMAC16 and UMAC32. The parameter sets have been chosen based on experimentation and provide good performance on a wide variety of processors. UMAC16 is designed to excel on processors which provide small-scale SIMD parallelism of the type found in Intel's MMX and Motorola's AltiVec instruction sets, while UMAC32 is designed to do well on processors with good 32- and 64- bit support. UMAC32 may take advantage of SIMD parallelism in future processors.
UMAC has been designed to allow implementations which accommodate on-line authentication. This means that pieces of the message may be presented to UMAC at different times (but in correct order) and an on-line implementation will be able to process the message correctly without the need to buffer more than a few dozen bytes of the message. For simplicity, the algorithms in this specification are presented as if the entire message being authenticated were available at once.
To authenticate a message, Msg, one first applies the
universal hash function, resulting in a string which is typically much
shorter than the original message. The pseudorandom function is applied to a
nonce, and the result is used in the manner of a Vernam cipher: the
authentication tag is the xor of the output from the hash function and the
output from the pseudorandom function. Thus, an authentication tag is
generated as
AuthTag = f(Nonce) xor h(Msg)
Here f is the pseudorandom function shared between the sender
and the receiver, and h is a universal hash function shared by the sender and
the receiver. In UMAC, a shared key is used to key the pseudorandom
function f, and then f is used for both tag
generation and internally to generate all of the bits needed by the universal
hash function.
The universal hash function that we use is called UHASH. It
combines several software-optimized algorithms into a multi-layered
structure. The algorithm is moderately complex. Some of this complexity comes
from extensive speed optimizations.
For the pseudorandom function we use the block cipher of the Advanced Encryption Standard (AES).
The UMAC32 parameters, considered in this implementation are:
UMAC32
------
WORD-LEN 4
UMAC-OUTPUT-LEN 8
L1-KEY-LEN 1024
UMAC-KEY-LEN 16
ENDIAN-FAVORITE BIG *
L1-OPERATIONS-SIGN UNSIGNED
Please note that this UMAC32 differs from the one described in the paper by the ENDIAN-FAVORITE value.
References:
| Modifier and Type | Field and Description |
|---|---|
static java.lang.String |
NONCE_MATERIAL
Property name of the user-supplied Nonce.
|
name, truncatedSize, underlyingHashMAC_KEY_MATERIAL, TRUNCATED_SIZE| Constructor and Description |
|---|
UMac32()
Trivial 0-arguments constructor.
|
| Modifier and Type | Method and Description |
|---|---|
java.lang.Object |
clone()
Returns a clone copy of this instance.
|
byte[] |
digest()
Completes the MAC by performing final operations such as
padding and resetting the instance.
|
void |
init(java.util.Map attributes)
Initialising a UMAC instance consists of defining values for
the following parameters:
|
int |
macSize()
Returns the output length in bytes of this MAC algorithm.
|
void |
reset()
Resets the algorithm instance for re-initialisation and use with other
characteristics.
|
boolean |
selfTest()
A basic test.
|
void |
update(byte b)
Continues a MAC operation using the input byte.
|
void |
update(byte[] b,
int offset,
int len)
Continues a MAC operation, by filling the buffer, processing
data in the algorithm's MAC_SIZE-bit block(s), updating the context and
count, and buffering the remaining bytes in buffer for the next
operation.
|
public static final java.lang.String NONCE_MATERIAL
public java.lang.Object clone()
IMacReturns a clone copy of this instance.
public int macSize()
IMacReturns the output length in bytes of this MAC algorithm.
public void init(java.util.Map attributes)
throws java.security.InvalidKeyException,
java.lang.IllegalStateException
Initialising a UMAC instance consists of defining values for the following parameters:
IMac.MAC_KEY_MATERIAL. The value is taken to be a byte array
containing the user-specified key material. The length of this array,
if/when defined SHOULD be exactly equal to KEY_LEN.NONCE_MATERIAL. The value is taken to be a byte array
containing the user-specified nonce material. The length of this array,
if/when defined SHOULD be (a) greater than zero, and (b) less or equal
to 16 (the size of the AES block).For convenience, this implementation accepts that not both parameters be always specified.
This method throws an exception if no Key Material is specified in the input map, and there is no previously set/defined Key Material (from an earlier invocation of this method). If a Key Material can be used, but no Nonce Material is defined or previously set/defined, then a default value of all-zeroes shall be used.
init in interface IMacinit in class BaseMacattributes - one or both of required parameters.java.security.InvalidKeyException - the key material specified is not of the
correct length.java.lang.IllegalStateException - if the instance is already initialised.IMac.MAC_KEY_MATERIALpublic void update(byte b)
IMacContinues a MAC operation using the input byte.
public void update(byte[] b,
int offset,
int len)
IMacContinues a MAC operation, by filling the buffer, processing data in the algorithm's MAC_SIZE-bit block(s), updating the context and count, and buffering the remaining bytes in buffer for the next operation.
public byte[] digest()
IMacCompletes the MAC by performing final operations such as padding and resetting the instance.
public void reset()
IMacResets the algorithm instance for re-initialisation and use with other characteristics. This method always succeeds.
public boolean selfTest()
IMacA basic test. Ensures that the MAC of a pre-determined message is equal to a known pre-computed value.
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