Shell script to play with ECB encryption.

ecbdemo.sh

#!/bin/sh

# Shell script to play with ECB encryption.
# Requires ImageMagick and OpenSSL commandline tools.
# See https://twitter.com/curtmackevo/status/1354471167793520641

while getopts f:o: c
do
    case $c
    in
        (f) IMAGE="$OPTARG";;
        (o) OUTPUT="$OPTARG";;
        (*) echo Unrecognized option $c; exit 1;;
    esac
done

if [ -z "$IMAGE" -o -z "$OUTPUT" ]
then
    echo "usage: $0 -f <image> -o <output>"
    exit 1
fi

# Get image properties
if identify "$IMAGE" > /dev/null 2>&1
then
    SIZE=`identify -format '%G' "$IMAGE"`
    DEPTH=`identify -format '%z' "$IMAGE"`
else
    echo "Not an image: $IMAGE"
    exit 1
fi

# We need two temporary files for conversions; we can swap back and
# forth between them
TMP1=`tempfile`
TMP2=`tempfile`

# Create random key
KEY=`openssl rand -hex 32`

# Convert the image to RGB
convert "$IMAGE" "rgb:$TMP1"

# Encrypt the image
openssl aes-256-ecb -e -K "$KEY" -in "$TMP1" -out "$TMP2"

# Convert back into a PNG at the output location
convert -size "$SIZE" -depth "$DEPTH" "rgb:$TMP2" "$OUTPUT"

# Delete temp files
rm "$TMP1" "$TMP2"