nnazo / csi3344-steganography Goto Github PK

• Add a seekNextIdat() function which calls find(DATA), then backs up by 8 bytes to read in idatPos (if this results in a value greater than TIPPING_POINT, call flip(idatPos)), then fast-forward 4 more bytes to put into the correct position.
• Update get() and put() to decrement idatPos for each byte read
• Update get() and put() to, before each read, check if idatPos is zero or less; if so, then call seekNextIdat() before getting/putting
• Add this same logic of tracking idatPos to flushAndClose()

Write one byte's worth of data into the RGB low-order bits. May want some helper functions. Be careful not to overflow image dimensions.

General strategy:

for each bit 'b' in the character:
    let c2 = peeked next character
    Embed  b in c2
    put c2 into stream (will overwrite original)

Returns the next hidden character. Must ensure it doesn't overshoot the end of the message.

Check to see if the number of bits in the provided message can be written into the provided file.

https://en.wikipedia.org/wiki/Cyclic_redundancy_check

Function CRC32
   Input:
      data:  Bytes     //Array of bytes
   Output:
      crc32: UInt32    //32-bit unsigned crc-32 value

//Initialize crc-32 to starting value
crc32 ← 0xFFFFFFFF

for each byte in data do
   nLookupIndex ← (crc32 xor byte) and 0xFF;
   crc32 ← (crc32 shr 8) xor CRCTable[nLookupIndex] //CRCTable is an array of 256 32-bit constants

//Finalize the CRC-32 value by inverting all the bits
crc32 ← crc32 xor 0xFFFFFFFF
return crc32

Embed a 4-byte length of the message a byte at a time using the put method before writing the actual message.

• getInput()

• Validate input mode, get the image file name, and either the message to embed or the destination of the message to extract.

• readMessage(const StegImage& imageToReadFrom, const string& filename)

• Read a message embedded in the StegImage. Will use StegImage::get

• writeMessage(const StegImage& imageToWriteTo, const string& messageToWrite)

• Put the message one character at a time

It's not 'Perex' it's 'Perez.' Way to go, me.

• Validate input after constructing StegImage

Add an errorMessage field to StegImage which is set by the constructor; this is populated by the constructor to match the cause which tripped the inError flag.

Takes a filename. Opens and must:

• Validate that it received a PNG
• Get the dimensions of the file. If they are unreasonable, correct from little endian
• Move the read/write heads to the pixel section
• ID bit depth