Package steganography.image

Class ImageSteg

java.lang.Object

steganography.image.ImageSteg

All Implemented Interfaces:

Steganography

public class ImageSteg
extends java.lang.Object
implements Steganography

Field Summary

Fields

Modifier and Type	Field	Description
static long	DEFAULT_SEED

Constructor Summary

Constructors

Constructor	Description
ImageSteg()	Creates a new ImageSteg with settings:
ImageSteg(boolean useDefaultHeader, boolean useTransparent)	Creates a new ImageSteg with the given settings.

Method Summary

Modifier and Type	Method	Description
byte[]	decode(byte[] steganographicData)	Decodes a hidden message in the given steganographicData (an image) and returns it as a byte array.
byte[]	decode(byte[] steganographicData, long seed)	Decodes a hidden message in the given steganographicData (an image) and returns it as a byte array.
byte[]	decodeRaw(int length, byte[] steganographicData)	Interprets an amount of (length * 8) pixels as a hidden message and returns it as a byte array.
byte[]	decodeRaw(int length, byte[] steganographicData, long seed)	Interprets an amount of (length * 8) pixels as a hidden message and returns it as a byte array.
byte[]	encode(byte[] carrier, byte[] payload)	Encodes the given payload in the given carrier (image, mp3, ...) and returns the result.
byte[]	encode(byte[] carrier, byte[] payload, long seed)	Encodes the given payload in the given carrier (image, mp3, ...) and returns the result.
int	getImageCapacity(byte[] image)	Returns the maximum number of bytes that can be encoded (as payload) in the given image.
boolean	isSteganographicData(byte[] data)	Tests whether the given data has a hidden message encoded in it.
boolean	isSteganographicData(byte[] data, long seed)	Tests whether the given data has a hidden message encoded in it.

Methods inherited from class java.lang.Object

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

Field Detail

DEFAULT_SEED

public static final long DEFAULT_SEED

See Also:

Constant Field Values

Constructor Detail

ImageSteg

public ImageSteg()

Creates a new ImageSteg with settings:

• useDefaultHeader = true
• useTransparent = false

This means, a default header will be encoded in the image to simplify decoding and fully transparent pixels will not be used for encoding or decoding.

This is equivalent to ImageSteg(true, false).

See Also:

ImageSteg(boolean, boolean)

ImageSteg

public ImageSteg(boolean useDefaultHeader,
                 boolean useTransparent)

Creates a new ImageSteg with the given settings.

useDefaultHeader

• if true, the default header will be encoded in the image. The hidden message can then be decoded using ImageSteg.decode(...).
• if false, no header will be encoded in the image. The hidden message can only be decoded using ImageSteg.decodeRaw(length, ...)

useTransparent

• if true, fully transparent pixels will be used for encoding and decoding
• if false, fully transparent pixels will not be used for encoding and decoding
• This value must be equal while encoding and decoding to successfully decode the hidden message.
• This value can only affect PNGs that contain fully transparent pixels.
• If an image has no fully transparent pixels, this value will be ignored.
• If the image is a GIF, this value will be ignored.
• BMPs with transparent pixels are not supported by this class.

Parameters:

useDefaultHeader - should the default header be used for encoding?

useTransparent - should fully transparent pixels be used for encoding and decoding?

See Also:

decode(byte[]), decode(byte[], long), decodeRaw(int, byte[]), decodeRaw(int, byte[], long)

Method Detail

encode

public byte[] encode(byte[] carrier,
                     byte[] payload)
              throws java.io.IOException,
                     UnsupportedImageTypeException,
                     NoImageException,
                     ImageWritingException,
                     ImageCapacityException

Description copied from interface: Steganography

Encodes the given payload in the given carrier (image, mp3, ...) and returns the result. The format of the returned media will be the same as carrier. Carrier needs to be an exact media representation as it would be read from a file by an InputStream.

Specified by:

encode in interface Steganography

Parameters:

carrier - media used to hide the payload

payload - data to hide

Returns:

steganographic data - exact media representation. Can be stored as it is to a file to open externally

Throws:

java.io.IOException - if a problem occurs during reading of carrier or payload

UnsupportedImageTypeException

NoImageException

ImageWritingException

ImageCapacityException

encode

public byte[] encode(byte[] carrier,
                     byte[] payload,
                     long seed)
              throws java.io.IOException,
                     NoImageException,
                     UnsupportedImageTypeException,
                     ImageWritingException,
                     ImageCapacityException

Description copied from interface: Steganography

Encodes the given payload in the given carrier (image, mp3, ...) and returns the result. The format of the returned media will be the same as carrier. Carrier needs to be an exact media representation as it would be read from a file by an InputStream.

The Seed changes the way the payload is encoded. When decoding the result, the exact same Seed needs to be given to decode()

Specified by:

encode in interface Steganography

Parameters:

carrier - media used to hide the payload

payload - data to hide

seed - affects the resulting steganographic data (similar to a password)

Returns:

steganographic data - exact media representation. Can be stored as it is to a file to open externally

Throws:

java.io.IOException - if a problem occurs during reading of carrier or payload

NoImageException

UnsupportedImageTypeException

ImageWritingException

ImageCapacityException

decode

public byte[] decode(byte[] steganographicData)
              throws java.io.IOException,
                     UnsupportedImageTypeException,
                     NoImageException,
                     UnknownStegFormatException

Decodes a hidden message in the given steganographicData (an image) and returns it as a byte array.

This method will fail, if the message was hidden without using the default header. Use ImageSteg.decodeRaw() for this purpose.

Reasons for failing with an UnknownStegFormatExceptions are:

• there is no hidden message
• the message was hidden with 'useDefaultHeader = false'
• the value for 'useTransparent' was different when hiding the message
• the message was hidden using an unknown algorithm

Specified by:

decode in interface Steganography

Parameters:

steganographicData - Image containing the hidden message to decode

Returns:

the hidden message as a byte array

Throws:

java.io.IOException - if an error occurs during reading 'steganographicData'

NoImageException - if no image could be read from 'steganographicData'

UnsupportedImageTypeException - if the type of the given image is not supported

UnknownStegFormatException - if the default header could not be found

See Also:

decodeRaw(int, byte[])

decode

public byte[] decode(byte[] steganographicData,
                     long seed)
              throws java.io.IOException,
                     NoImageException,
                     UnsupportedImageTypeException,
                     UnknownStegFormatException

Decodes a hidden message in the given steganographicData (an image) and returns it as a byte array.

This method will fail, if the message was hidden without using the default header. Use ImageSteg.decodeRaw() for this purpose.

Reasons for failing with an UnknownStegFormatExceptions are:

• there is no hidden message
• the message was hidden with 'useDefaultHeader = false'
• the value for 'useTransparent' was different when hiding the message
• the message was hidden using an unknown algorithm

Specified by:

decode in interface Steganography

Parameters:

steganographicData - Image containing the hidden message to decode

seed - seed that was used to encode the given stenographicData

Returns:

the hidden message as a byte array

Throws:

java.io.IOException - if an error occurs during reading 'steganographicData'

NoImageException - if no image could be read from 'steganographicData'

UnsupportedImageTypeException - if the type of the given image is not supported

UnknownStegFormatException - if the default header could not be found

See Also:

decodeRaw(int, byte[], long)

decodeRaw

public byte[] decodeRaw(int length,
                        byte[] steganographicData)
                 throws java.io.IOException,
                        NoImageException,
                        UnsupportedImageTypeException

Interprets an amount of (length * 8) pixels as a hidden message and returns it as a byte array.

This method will not search for a header or validate the retrieved data in any form. If 'steganographicData' contains a supported image, this method will always return a result. Whether this result is the hidden message, depends on the settings used:

• 'useTransparent' during encoding == 'useTransparent' during decoding
• 'payload.length' during encoding == 'length' during decoding
• No seed used during encoding (thereby using ImageSteg.DEFAULT_SEED)
• 'useDefaultHeader' == false during encoding

Parameters:

length - Length (in bytes) of the hidden message

steganographicData - Data containing data to extract

Returns:

a byte array of length == "length" as a result of decoding (length * 8) pixels

Throws:

java.io.IOException - if an error occurs during reading 'steganographicData'

NoImageException - if no image could be read from 'steganographicData'

UnsupportedImageTypeException - if the type of the given image is not supported

decodeRaw

public byte[] decodeRaw(int length,
                        byte[] steganographicData,
                        long seed)
                 throws java.io.IOException,
                        NoImageException,
                        UnsupportedImageTypeException

Interprets an amount of (length * 8) pixels as a hidden message and returns it as a byte array.

This method will not search for a header or validate the retrieved data in any form. If 'steganographicData' contains a supported image, this method will always return a result. Whether this result is the hidden message, depends on the settings used:

• 'useTransparent' during encoding == 'useTransparent' during decoding
• 'payload.length' during encoding == 'length' during decoding
• 'seed' during encoding == 'seed' during decoding
• 'useDefaultHeader' == false during encoding

Parameters:

length - Length (in bytes) of the hidden message

steganographicData - Data containing data to extract

seed - seed that was used to encode the given stenographicData

Returns:

a byte array of length == "length" as a result of decoding (length * 8) pixels

Throws:

java.io.IOException - if an error occurs during reading 'steganographicData'

NoImageException - if no image could be read from 'steganographicData'

UnsupportedImageTypeException - if the type of the given image is not supported

isSteganographicData

public boolean isSteganographicData(byte[] data)
                             throws java.io.IOException,
                                    NoImageException,
                                    UnsupportedImageTypeException

Description copied from interface: Steganography

Tests whether the given data has a hidden message encoded in it. This method only works if the message was encoded using the given Seed or the respective default Seed. Otherwise it will always return false.

The use of this method is discouraged. It saves very little resources compared to decode(...). So unless you need to test a lot of possible steganographicData, just use decode(...) and catch the UnknownStegFormatException

Specified by:

isSteganographicData in interface Steganography

Parameters:

data - data to test

Returns:

true if the given data has a hidden message encoded in it

Throws:

java.io.IOException - if a problem occurs during reading of data

NoImageException

UnsupportedImageTypeException

isSteganographicData

public boolean isSteganographicData(byte[] data,
                                    long seed)
                             throws java.io.IOException,
                                    NoImageException,
                                    UnsupportedImageTypeException

Description copied from interface: Steganography

Tests whether the given data has a hidden message encoded in it. This method only works if the message was encoded using the given Seed. Otherwise it will always return false.

The use of this method is discouraged. It saves very little resources compared to decode(...). So unless you need to test a lot of possible steganographicData, just use decode(...) and catch the UnknownStegFormatException

Specified by:

isSteganographicData in interface Steganography

Parameters:

data - data to test

seed - seed the hidden message was encoded with

Returns:

true if the given data has a hidden message encoded in it

Throws:

java.io.IOException - if a problem occurs during reading of data

NoImageException

UnsupportedImageTypeException

getImageCapacity

public int getImageCapacity(byte[] image)
                     throws java.io.IOException,
                            NoImageException,
                            UnsupportedImageTypeException

Returns the maximum number of bytes that can be encoded (as payload) in the given image. This method accounts for the use of transparent pixels and default header as given to the constructor.

Parameters:

image - image to potentially encode bytes in

Returns:

the payload-capacity of image

Throws:

java.io.IOException - if an error occurs during reading the image

NoImageException - if no image could be read from the image

UnsupportedImageTypeException - if the type of the given image is not supported

See Also:

ImageSteg(boolean, boolean)