Top Description Fields Constructors Methods
org.bouncycastle.crypto.generators

public Class Poly1305KeyGenerator

extends CipherKeyGenerator
Class Inheritance
Imports
org.bouncycastle.crypto.CipherKeyGenerator, .KeyGenerationParameters, org.bouncycastle.crypto.macs.Poly1305
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

Modifier and TypeField and Description
private static final byte
R_MASK_HIGH_4

private static final byte
R_MASK_LOW_2

Inherited from org.bouncycastle.crypto.CipherKeyGenerator:
randomstrength

Constructor Summary

AccessConstructor and Description
public
Poly1305KeyGenerator()

Method Summary

Modifier and TypeMethod and Description
public static void
checkKey(byte[] key)

Checks a 32 byte key for compliance with the Poly1305 key requirements, e.g. k[0] ...

private static void
checkMask(byte b, byte mask)

public static void
clamp(byte[]
a 32 byte key value k[0] ... k[15], r[0] ... r[15]
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.

public byte[]
generateKey()

Overrides org.bouncycastle.crypto.CipherKeyGenerator.generateKey.

Generates a 256 bit key in the format required for Poly1305 - e.g. k[0] ...

public void
init(KeyGenerationParameters
the parameters to be used for key generation
param)

Overrides org.bouncycastle.crypto.CipherKeyGenerator.init.

Initialises the key generator.

Field Detail

R_MASK_HIGH_4back to summary
private static final byte R_MASK_HIGH_4
R_MASK_LOW_2back to summary
private static final byte R_MASK_LOW_2

Constructor Detail

Poly1305KeyGeneratorback to summary
public Poly1305KeyGenerator()

Method Detail

checkKeyback to summary
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[]).

Exceptions
IllegalArgumentException:
if the key is of the wrong length, or has invalid bits set in the r portion of the key.
checkMaskback to summary
private static void checkMask(byte b, byte mask)
clampback to summary
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:byte[]

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

generateKeyback to summary
public byte[] generateKey()

Overrides org.bouncycastle.crypto.CipherKeyGenerator.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[]).

Returns:byte[]

Doc from org.bouncycastle.crypto.CipherKeyGenerator.generateKey.

a byte array containing the key value.

initback to summary
public void init(KeyGenerationParameters param)

Overrides org.bouncycastle.crypto.CipherKeyGenerator.init.

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

Parameters
param:KeyGenerationParameters

Doc from org.bouncycastle.crypto.CipherKeyGenerator.init.

the parameters to be used for key generation