CODEWITHSUNDEEP
objective-cimageencryptioncryptography
chikuba
chikuba

Reputation: 4357

Encrypt / Decrypt uidata with "homemade" algorithm

Just working on a algorithm and so far i can encrypt and decrypt a number, which works fine. My question now is how do i go abouts encrypting an image? How does the UIdata look and shold i convert the image to that before I start? Never done anything on this level in terms of encryption and any input would be great! Thanks!

Upvotes: 0

Views: 263

Answers (2)

Paŭlo Ebermann
Paŭlo Ebermann

Reputation: 74810

I don't know the signature of your algorithm (i.e. what types of input it takes and what types output it gives), but the most common ciphers are block ciphers, i.e. algorithms which have a input of some block size (nowadays 128 bits = 16 bytes is a common size), and a same-sized output, additionally to a key input (which should also have at least 128 bits).

To encrypt longer pieces of data (and actually, also for short pieces if you send multiple such pieces with the same key), you use a mode of operation (and probably additionally a padding scheme). This gives you an algorithm (or a pair of such) with an arbitrary length plaintext input, and slightly bigger ciphertext output (which the decryption algorithm undoes then).

Some hints:

  • Don't use ECB mode (i.e. simply encrypting each block independently of the others).
  • Probably you also should apply a MAC, to protect your data against malicious modifications (and also breaking of the encryption scheme by choosen-ciphertext attacks). Some modes of operation already include a MAC.

Upvotes: 1

Kevin
Kevin

Reputation: 56129

You'll probably want to encrypt in small chunks - perhaps a byte or word/int (4 bytes), maybe even a long (8 bytes) at a time depending on how your algorithm is implemented.

Upvotes: 1

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