display an image encrypted with ECB

Question

On wikipedia there is an example of a picture encrypted with ECB:

http://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#Electronic_codebook_.28ECB.29

I just wanted to know how an encrypted file could be displayed as a picture ?

This question is really about how to read arbitrary data as an image and should be perhaps on StackOverflow or some other site. — fkraiem, Jan 23 '15 at 05:15
See this blog post for a detailed account of how to generate ECB penguins — Mikero, Jan 23 '15 at 05:42
great link @Mikero, if I understand correctly it doesn't work with jpg or png and if you don't know the size of the picture? — David 天宇 Wong, Jan 23 '15 at 05:52
It doesn't work with compressed files for obvious reasons: the encrypted data may very well not be valid compressed data (which can be decompressed). And you need to know at least one of the width or height of the picture in order to be able to tell where each row of the picture ends and the next begins. — fkraiem, Jan 23 '15 at 06:13

score 2 · Answer 1 · answered Jan 23 '15 at 05:14

This is off-topic, but arbitrary binary data can be read as image data using for example the Netpbm family of file formats. For example, here's how to read 10000 bytes of random data as a 100x100 grayscale image:

$ cat > image.pgm
    P2
    100 100 255
    ^C                             
    $ dd if=/dev/urandom of=image.raw bs=10000 count=1
1+0 records in
1+0 records out
10000 bytes transferred in 0.001229 secs (8136380 bytes/sec)
$ od -A n -t u1 image.raw >> image.pgm

You can then open image.pgm for example in Gimp.

display an image encrypted with ECB

1 Answers1