ch.epfl.dedis.calypso

Class Document

java.lang.Object

ch.epfl.dedis.calypso.Document

public class Document
extends Object

A document is an example how to use Calypso to store a document securely on Byzcoin. The document class always holds the data unencrypted, but encrypts - the data using the keyMaterial - the keyMaterial using the public key of the Long Term Secrets

It can return the document if it is given a ReadInstance and the private key to decrypt the keyMaterial.

Constructor Summary

Constructors

Constructor and Description
Document(byte[] data, byte[] keyMaterial, byte[] extraData, DarcId publisherId) Initialises a document.
Document(byte[] data, int keylen, byte[] extraData, DarcId publisherId) Creates a new document from data, creates a new Darc, a symmetric symmetricKey and encrypts the data using CBC-RSA.

Method Summary

Modifier and Type	Method and Description
boolean	equals(Object other) Compares this document with another document.
static Document	fromCalypso(CalypsoRPC calypso, InstanceId riId, Scalar reader) Fetches a document from calypso, once the read instance has been created.
static Document	fromWriteInstance(WriteInstance wi, byte[] keyMaterial) Recreate the document once all the material already is fetched from ByzCoin.
byte[]	getData()
byte[]	getExtraData()
byte[]	getKeyMaterial()
DarcId	getPublisherId()
WriteData	getWriteData(LTS lts) Creates a WriteData object with the fields of the document.
WriteInstance	spawnWrite(CalypsoRPC calypso, DarcId publisherDarcId, Signer publisherSigner) Creates a new WriteInstance with the document stored in it.
String	toString()

Methods inherited from class java.lang.Object

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

Constructor Detail

Document

public Document(byte[] data,
                byte[] keyMaterial,
                byte[] extraData,
                DarcId publisherId)
         throws CothorityCryptoException

Initialises a document. The data already has to be encrypted.

Parameters:

data - the data that will be encrypted using the keyMaterial

keyMaterial - key-material necessary for the unencryption of the document. This will be encrypted before the transmission to the skipchain.

extraData - any public data that will be stored unencrypted on the skipchain.

publisherId - the publisher darc with the rules to create a WriteInstance and a ReadInstance.

Throws:

CothorityCryptoException - in the case the encryption doesn't work

Document

public Document(byte[] data,
                int keylen,
                byte[] extraData,
                DarcId publisherId)
         throws CothorityCryptoException

Creates a new document from data, creates a new Darc, a symmetric symmetricKey and encrypts the data using CBC-RSA.

Parameters:

data - any data that will be stored encrypted on the skipchain. There is a 10MB-limit on how much data can be stored. If you need more, this must be a pointer to an off-chain storage.

keylen - how long the symmetric symmetricKey should be, in bytes. 16 bytes should be a safe guess for the moment.

extraData - any public data that will not be encrypted

publisherId - the publisher darc with the rules to create a WriteInstance and a ReadInstance.

Throws:

CothorityCryptoException - in the case the encryption doesn't work

Method Detail

getWriteData

public WriteData getWriteData(LTS lts)
                       throws CothorityException

Creates a WriteData object with the fields of the document.

Parameters:

lts - the Long Term Secret to use.

Returns:

a WriteData with the encrypted data

Throws:

CothorityException

spawnWrite

public WriteInstance spawnWrite(CalypsoRPC calypso,
                                DarcId publisherDarcId,
                                Signer publisherSigner)
                         throws CothorityException

Creates a new WriteInstance with the document stored in it.

Parameters:

calypso - an instance of the calypsoRPC

publisherDarcId - a darc with a 'spawn:calypsoWrite' rule

publisherSigner - a signer having the right to trigger the 'spawn:calypsoWrite' rule.

Returns:

a WriteInstance

Throws:

CothorityException

equals

public boolean equals(Object other)

Compares this document with another document. If this document has a writeRequestId, it will be compared against the other document's writeRequestId, else it will be ignored.

Overrides:

equals in class Object

Parameters:

other - another Document

Returns:

true if both are equal

getKeyMaterial

public byte[] getKeyMaterial()

Returns:

the key material used to encrypt the data

getExtraData

public byte[] getExtraData()

Returns:

the public data that is stored in cleartext on ByzCoin

getPublisherId

public DarcId getPublisherId()

Returns:

the darcId protecting access to this document.

getData

public byte[] getData()
               throws CothorityCryptoException

Returns:

the decrypted data stored in this document.

Throws:

CothorityCryptoException

toString

public String toString()

Overrides:

toString in class Object

Returns:

a nicely formatted string representing the document.

fromCalypso

public static Document fromCalypso(CalypsoRPC calypso,
                                   InstanceId riId,
                                   Scalar reader)
                            throws CothorityException

Fetches a document from calypso, once the read instance has been created. It fetches the ReadInstance, WriteInstance, and the reader darc from ByzCoin, and then re-creates a document with the decrypted keyMaterial and decrypted data.

Parameters:

calypso - an existing calypso

riId - the instance Id of the read instance

reader - the private key of the reader (or ephemeral key)

Returns:

the document with the decrypted keyMaterial and decrypted data

Throws:

CothorityException

com.google.protobuf.InvalidProtocolBufferException

fromWriteInstance

public static Document fromWriteInstance(WriteInstance wi,
                                         byte[] keyMaterial)
                                  throws CothorityNotFoundException,
                                         CothorityCryptoException

Recreate the document once all the material already is fetched from ByzCoin.

Parameters:

wi - WriteInstance for this document

keyMaterial - the decrypted key material

Returns:

a new Document with the decrypted data

Throws:

CothorityNotFoundException

CothorityCryptoException