You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
42 lines
1.5 KiB
Markdown
42 lines
1.5 KiB
Markdown
# Cryptpng
|
|
|
|
A proof of concept implementation of storing encrypted data inside of png metadata chunks.
|
|
|
|
## Usage
|
|
|
|
```shell script
|
|
# encrypt
|
|
cryptpng --image <name of the image> --in <input file> --out <output file>
|
|
|
|
# decrypt
|
|
cryptpng --decrypt --image <crypt image> --out <decrypted output file>
|
|
```
|
|
|
|
## Technical Information
|
|
|
|
It should be possible to store data with a size up to ~ 4GB, but in reality most image viewers have
|
|
problems with chunks that are bigger than several Megabytes.
|
|
The data itself is stored in a [png chunk](http://www.libpng.org/pub/png/spec/1.2/PNG-Structure.html)
|
|
and encrypted via aes. The encryption chunk is stored right before the `IDAT` chunk that contains the
|
|
image data. The steps for encrypting are:
|
|
|
|
### Encrypt
|
|
|
|
1. Parse the png file and split it into chunks.
|
|
2. Prompt for a password and use the sha512 32byte value with a generated salt.
|
|
3. Store the salt in the `saLt` chunk.
|
|
4. Create a base64 string out of the data.
|
|
5. Encrypt the base64 string using aes and the provided hashed key.
|
|
6. Split the data into parts of 1 MiB of size.
|
|
7. Store every data part into a separate `crPt` chunk.
|
|
8. Write the png header and chunks to the output file.
|
|
|
|
### Decrypt
|
|
|
|
1. Parse the png file and split it into chunks.
|
|
2. Get the `saLt` chunk.
|
|
3. Get the `crPt` chunks and and concat the data.
|
|
4. Prompt for the password and create the sha512 32byte hash with the salt.
|
|
5. Decrypt the data using aes and the provided hash key.
|
|
6. Decode the base64 data.
|
|
7. Write the data to the specified output file. |