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39 lines
1.3 KiB
Markdown
39 lines
1.3 KiB
Markdown
# Cryptpng
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A proof of concept implementation of storing encrypted data inside of png metadata chunks.
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## Usage
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```shell script
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# encrypt
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cryptpng --image <name of the image> --in <input file> --out <output file>
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# decrypt
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cryptpng --decrypt --image <crypt image> --out <decrypted output file>
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```
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## Technical Information
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It should be possible to store data with a size up to ~ 4GB, but in reality most image viewers have
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problems with chunks that are bigger than several Megabytes.
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The data itself is stored in a [png chunk](http://www.libpng.org/pub/png/spec/1.2/PNG-Structure.html)
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and encrypted via aes. The encryption chunk is stored right before the `IDAT` chunk that contains the
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image data. The steps for encrypting are:
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### Encrypt
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1. Parse the png file and split it into chunks.
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2. Prompt for a password and use the sha512 32byte value.
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3. Create a base64 string out of the data.
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4. Encrypt the base64 string using aes and the provided hashed key.
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5. Store the data into the `crPt` chunk.
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6. Write the png header and chunks to the output file.
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### Decrypt
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1. Parse the png file and split it into chunks.
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2. Get the `crPt` chunk.
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3. Prompt for the password and create the sha512 32byte hash.
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4. Decrypt the data using aes and the provided hash key.
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5. Decode the base64 data.
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6. Write the data to the specified output file. |