Encrypt .ppm file with AES-ECB to show ECB will reveal patterns

encrypt_img_ecb.sh

#!/bin/sh

# This is part of my blog about AES: https://medium.com/p/7616beaaade9
# Inspired by https://blog.filippo.io/the-ecb-penguin/

# Convert your image to .ppm with Gimp or Photoshop
#
# Usage: ./ecb_img <image file as ppm> <password>

# extract header and body
head -n 4 $1 > $1.header.txt
tail -n +5 $1 > $1.body.bin

# encrypt with ecb and given password
openssl enc -aes-128-ecb -nosalt -pass pass:"$2" -in  $1.body.bin -out $1.body.ecb.bin

# reassemble image
cat $1.header.txt $1.body.ecb.bin > $1.ecb.ppm

# Clean up temp files
rm $1.header.txt
rm $1.body.bin
rm $1.body.ecb.bin

echo "encrypted image to $1.ecb.ppm"

The number of header lines depends on the whitespaces used: https://netpbm.sourceforge.net/doc/ppm.html

If spaces are used, then there is only one header line. If next line characters are used, then you would need four. Anything in between is fair game.

A more robust implementation would account for different whitespaces.