org.bouncycastle.crypto.generators

Class Poly1305KeyGenerator

java.lang.Object

org.bouncycastle.crypto.CipherKeyGenerator

org.bouncycastle.crypto.generators.Poly1305KeyGenerator

public class Poly1305KeyGenerator
extends CipherKeyGenerator

Generates keys for the Poly1305 MAC.

Poly1305 keys are 256 bit keys consisting of a 128 bit secret key used for the underlying block cipher followed by a 128 bit r value used for the polynomial portion of the Mac.
The r value has a specific format with some bits required to be cleared, resulting in an effective 106 bit key.
A separately generated 256 bit key can be modified to fit the Poly1305 key format by using the clamp(byte[]) method to clear the required bits.

See Also:

Poly1305

Field Summary

Fields inherited from class org.bouncycastle.crypto.CipherKeyGenerator

random, strength

Constructor Summary

Constructors

Constructor and Description
Poly1305KeyGenerator()

Method Summary

Methods

Modifier and Type	Method and Description
static void	checkKey(byte[] key) Checks a 32 byte key for compliance with the Poly1305 key requirements, e.g.
static void	clamp(byte[] key) Modifies an existing 32 byte key value to comply with the requirements of the Poly1305 key by clearing required bits in the r (second 16 bytes) portion of the key. Specifically: r[3], r[7], r[11], r[15] have top four bits clear (i.e., are {0, 1, .
byte[]	generateKey() Generates a 256 bit key in the format required for Poly1305 - e.g.
void	init(KeyGenerationParameters param) Initialises the key generator. Poly1305 keys are always 256 bits, so the key length in the provided parameters is ignored.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Poly1305KeyGenerator

public Poly1305KeyGenerator()

Method Detail

init

public void init(KeyGenerationParameters param)

Initialises the key generator.
Poly1305 keys are always 256 bits, so the key length in the provided parameters is ignored.

Overrides:

init in class CipherKeyGenerator

Parameters:

param - the parameters to be used for key generation

generateKey

public byte[] generateKey()

Generates a 256 bit key in the format required for Poly1305 - e.g. k[0] ... k[15], r[0] ... r[15] with the required bits in r cleared as per clamp(byte[]).

Overrides:

generateKey in class CipherKeyGenerator

Returns:

a byte array containing the key value.

clamp

public static void clamp(byte[] key)

Modifies an existing 32 byte key value to comply with the requirements of the Poly1305 key by clearing required bits in the r (second 16 bytes) portion of the key.
Specifically:

• r[3], r[7], r[11], r[15] have top four bits clear (i.e., are {0, 1, . . . , 15})
• r[4], r[8], r[12] have bottom two bits clear (i.e., are in {0, 4, 8, . . . , 252})

Parameters:

key - a 32 byte key value k[0] ... k[15], r[0] ... r[15]

checkKey

public static void checkKey(byte[] key)

Checks a 32 byte key for compliance with the Poly1305 key requirements, e.g. k[0] ... k[15], r[0] ... r[15] with the required bits in r cleared as per clamp(byte[]).

Throws:

IllegalArgumentException - if the key is of the wrong length, or has invalid bits set in the r portion of the key.