Decode information from European covid19 travel certificates

eu-covid-certificate-qr-decoder.py

#######
# 
# REQUIRES: pip install cose  #!!!!
#
# HOW TO USE:
# 1. Use your favourite QR scanner to scan the code from a certificate, 
#    you'll get a string that starts with "HC1:"
# 2. Run the script: python3 covid-qr-certificate-decoder.py
# 3. Paste the string when prompted
#
#
# READING (how to interpret the output and test data):
# api spec: https://github.com/eu-digital-green-certificates/dgca-issuance-web/blob/main/src/generated-files/dgc-combined-schema.d.ts
# https://github.com/eu-digital-green-certificates/dgca-issuance-web/blob/main/src/misc/edgcProcessor.tsx
# https://github.com/admin-ch/CovidCertificate-Examples
# https://github.com/eu-digital-green-certificates/dgc-testdata/tree/main/PL
#
#######


from typing import Union
import zlib
from cose.messages import CoseMessage
import cbor2
import pprint
import json

# example code for testing
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

# credits: https://github.com/kirei/python-base45/blob/main/base45/__init__.py
def b45decode(s: Union[bytes, str]) -> bytes:
    """Decode base45-encoded string to bytes"""
    BASE45_CHARSET = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ $%*+-./:"
    res = []
    try:
        if isinstance(s, str):
            buf = [BASE45_CHARSET.index(c) for c in s]
        else:
            buf = [BASE45_CHARSET.index(c) for c in s.decode()]
        buflen = len(buf)
        for i in range(0, buflen, 3):
            x = buf[i] + buf[i + 1] * 45
            if buflen - i >= 3:
                x = buf[i] + buf[i + 1] * 45 + buf[i + 2] * 45 * 45
                res.extend(list(divmod(x, 256)))
            else:
                res.append(x)
        return bytes(res)
    except (ValueError, IndexError, AttributeError):
        raise ValueError("Invalid base45 string")


def main() -> None:
    data = input("Paste the decoded QR code string and press Enter:\n")
    if data.startswith('HC1:'): data = data[4:]
    decoded = b45decode(data)
    decompressed = zlib.decompress(decoded);
    msg = CoseMessage.decode(decompressed);
    phdr, uhdr = msg._hdr_repr()
    payload = cbor2.loads(msg.payload)

    #payload is the most interesting part, the others are rather boring
    print("\n")
    print("==PHDR==\n")
    pprint.pprint(phdr)
    print("==UHDR==\n")
    pprint.pprint(uhdr)
    #print("==SIGNATURE==\n",msg.signature,"\n")
    print("==PAYLOAD==")
    print(json.dumps(payload, ensure_ascii=False, indent=4))
    print("\n")

if __name__ == "__main__":
    main()

Hey thank you for this snippet! Do you know where and how I could verify the signature?

@matze-anyline Check out the official, example implementations of mobile apps:

• https://github.com/eu-digital-green-certificates/dgca-verifier-app-ios
• https://github.com/eu-digital-green-certificates/dgca-verifier-app-android
• https://github.com/eu-digital-green-certificates/dgca-verifier-service (backend for the apps)

Can't tell if they are working (I had troubles with running them) but reading the code can give you an idea how to implement a verification procedure.

Possible to reverse the process and create new QR code based on new informations ?

Possible to reverse the process and create new QR code based on new informations ?

Have you found a method?

Possible to reverse the process and create new QR code based on new informations ?

Any findings so far?

Problem is that the information is hashed and signed via a private key, wich only certain authorities have access to.
The check apps then check this signing via a public key.
So yes it's relatively easy to create a new QR code based on new information, but you won't get a valid vaccination status in any check app.

Strange, the script works if I run it in the same file, but if I pass the data as string from another script it throws an error:

pi@raspberrypi:~/app $ python3 123.py
Traceback (most recent call last):
File "/home/pi/app/decoder.py", line 38, in b45decode
buf = [BASE45_CHARSET.index(c) for c in s]
File "/home/pi/app/decoder.py", line 38, in
buf = [BASE45_CHARSET.index(c) for c in s]
ValueError: substring not found

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "123.py", line 27, in
decoder.main(data)
File "/home/pi/app/decoder.py", line 57, in main
decoded = b45decode(data)
File "/home/pi/app/decoder.py", line 51, in b45decode
raise ValueError("Invalid base45 string")
ValueError: Invalid base45 string

Any idea about how to find and break this private key in order to have a valid signature?

Any idea about how to find and break this private key in order to have a valid signature?

Nothing found yet

Found this : https://www.zofrex.com/blog/2020/10/20/alg-none-jwt-nhs-contact-tracing-app/
Unfortunately it seems this is already settled.

Found this : https://www.zofrex.com/blog/2020/10/20/alg-none-jwt-nhs-contact-tracing-app/ Unfortunately it seems this is already settled.

Good finding

greetings gentlemen. I confirm, that the reverse process of creating a new qr code (based on the new input information) does work nicely, however the issue with the verification makes the qr code invalid in the app. I hope a clever solution will come up.

That's pretty normal because all the datas are hashed with a primary key that we have no idea about...
Every primary key is unique and directly registered to the national database. So instead of directly hacking this database, I'm not sure that there is so many other solutions... We can consider that this system is inviolable.

@fjusufi-ubt it happened to you, so it might help you: When I copied the qrcode, it had two "HC1:", so if you divide it into two different qrcodes may work for you, it did in my case. I hope it helps

@DavidBor17 could you help me to make a valid GP?

@krajcit Hey sir, can you provide me your source code allowing to put new input information in the qr code pls ?
I'm trying to create one since 2 days but without sucess...

@krajcit Hello! Please send me your source code to qreate QR with new input information? It's very important for me and it's for me only)))