com.google.crypto.tink.subtle

Class Kwp

java.lang.Object

com.google.crypto.tink.subtle.Kwp

All Implemented Interfaces:

KeyWrap

public class Kwp
extends Object
implements KeyWrap

Implements the key wrapping primitive KWP defined in NIST SP 800 38f. The same encryption mode is also defined in RFC 5649. The NIST document is used here as a primary reference, since it contains a security analysis and further recommendations. In particular, Section 8 of NIST SP 800 38f suggests that the allowed key sizes may be restricted. The implementation in this class requires that the key sizes are in the range MIN_WRAP_KEY_SIZE and MAX_WRAP_KEY_SIZE.

The minimum of 16 bytes has been chosen, because 128 bit keys are the smallest key sizes used in tink. Additionally, wrapping short keys with KWP does not use the function W and hence prevents using security arguments based on the assumption that W is strong pseudorandom. (I.e. one consequence of using a strong pseudorandom permutation as an underlying function is that leaking partial information about decrypted bytes is not useful for an attack.)

The upper bound for the key size is somewhat arbitrary. Setting an upper bound is motivated by the analysis in section A.4 of NIST SP 800 38f: forgeries of long messages is simpler than forgeries of short message.

Since:

1.?.?

Constructor Summary

Constructors

Constructor and Description
Kwp(byte[] key) Construct a new Instance for KWP.

Method Summary

Modifier and Type	Method and Description
byte[]	unwrap(byte[] data) Unwraps a wrapped key.
byte[]	wrap(byte[] data) Wraps some key material data.

Methods inherited from class java.lang.Object

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

Constructor Detail

Kwp

public Kwp(byte[] key)
    throws GeneralSecurityException

Construct a new Instance for KWP.

Parameters:

key - the wrapping key. This is an AES key. Supported key sizes are 128 and 256 bits.

Throws:

GeneralSecurityException

Method Detail

wrap

public byte[] wrap(byte[] data)
            throws GeneralSecurityException

Wraps some key material data.

Specified by:

wrap in interface KeyWrap

Parameters:

data - the key to wrap.

Returns:

the wrapped key

Throws:

GeneralSecurityException

unwrap

public byte[] unwrap(byte[] data)
              throws GeneralSecurityException

Unwraps a wrapped key.

Specified by:

unwrap in interface KeyWrap

Throws:

GeneralSecurityException - if data fails the integrity check.