Decoding EU Digital COVID Certificate
Friday, August 6. 2021
If you live in EU, you most definitely have heard of COVID Passport.
Practically speaking, it is a PDF-file A4-sized when printed and can be folded into A6-pocket size. In Finland a sample would look like this:
What's eye-catching is the QR-code in the top right corner. As I'm into all kinds of nerdy stuff, I took a peek what's in it.
After reading some specs and brochures (like https://www.kanta.fi/en/covid-19-certificate) I started to tear this apart and deduced following:
- An A4 or the QR-code in it can be easily copied / duplicated
- Payload can be easily forged
- There is a claim: "The certificate has a code for verifying the authenticity"
My only question was: How is this sane! Why do they think this mechanism they designed makes sense?
QR-code
Data in QR-code is wrapped multiple times:
This CBOR Object Signing and Encryption (COSE) described in RFC 8152 was a new one for me.
Payload does contain very little of your personal information, but enough to be compared with your ID-card or passport. Also there is your vaccination, test and possible recovery from COVID statuses. Data structure can contain 1, 2 or 3 of those depending if you have been vaccinated or tested, or if you have recovered from the illness.
Python code
It's always about the details. So, I forked an existing git-repo and did some of my own tinkering. Results are at: https://github.com/HQJaTu/vacdec/tree/certificate-fetch
Original code by Mr. Hanno Böck could read QR-code and do some un-wrapping for it to reveal the payload. As I'm always interested in X.509, digital signatures and cryptography, I improved his code by incorporating the digital signature verification into it.
As CBOR/COSE was new for me, it took a while to get the thing working. In reality the most difficult part was to get my hands into the national public certificates to do some ECDSA signature verifying. It's really bizarre how that material is not made easily available.
Links:
- Swagger of DGC-gateway: https://eu-digital-green-certificates.github.io/dgc-gateway/
- This is just for display-purposes, this demo isn't connected to any of the national back-ends
- Sample data for testing verification: https://github.com/eu-digital-green-certificates/dgc-testdata
- All participating nations included
- QR-codes and raw-text ready-to-be-base45-decoded
- Payload JSON_schema: https://github.com/ehn-dcc-development/ehn-dcc-schema/
- Just to be clear, the payload is not JSON
- However, CBOR is effectively binary JSON
- List of all production signature certificates: https://dgcg.covidbevis.se/tp/
- Austrian back-end trust-list in JSON/CBOR: https://greencheck.gv.at/api/masterdata
- Swedish back-end trust-list in CBOR: https://dgcg.covidbevis.se/tp/trust-list
- The idea is for all national back-ends to contain everybody's signing certificate
Wallet
Mr. Philipp Trenz from Germany wrote a website to insert your QR-code into your Apple Wallet. Source is at https://github.com/philipptrenz/covidpass and the actual thing is at https://covidpass.eu/
Beautiful! Works perfectly.
Especially in Finland the government is having a vacation. After that they'll think about starting to make plans what to do next. Now thanks to Mr. Trenz every iOS user can have the COVID Certificate in their phones without government invovement.
Finally
Answers:
- Yes, duplication is possible, but not feasible in volume. You can get your hands into somebody else's certificate and can present a proof of vaccination, but verification will display the original name, not yours.
- Yes, there is even source code for creating the QR-code, so it's very easy to forge.
- Yes, the payload has a very strong elliptic curve signature in it. Any forged payloads won't verify.
Ultimately I was surprised how well designed the entire stack is. It's always nice to see my tax-money put into good use. I have nothing negative to say about the architecture or technologies used.
Bonus:
At very end of my project, I bumped into Mr. Mathias Panzenböck's code https://github.com/panzi/verify-ehc/. He has an excellent implementation of signature handling, much better than mine. Go check that out too.
If you live in EU, you most definitely have heard of COVID Passport.
Practically speaking, it is a PDF-file A4-sized when printed and can be folded into A6-pocket size. In Finland a sample would look like this:
What's eye-catching is the QR-code in the top right corner. As I'm into all kinds of nerdy stuff, I took a peek what's in it.
After reading some specs and brochures (like https://www.kanta.fi/en/covid-19-certificate) I started to tear this apart and deduced following:
- An A4 or the QR-code in it can be easily copied / duplicated
- Payload can be easily forged
- There is a claim: "The certificate has a code for verifying the authenticity"
My only question was: How is this sane! Why do they think this mechanism they designed makes sense?
QR-code
Data in QR-code is wrapped multiple times:
This CBOR Object Signing and Encryption (COSE) described in RFC 8152 was a new one for me.
Payload does contain very little of your personal information, but enough to be compared with your ID-card or passport. Also there is your vaccination, test and possible recovery from COVID statuses. Data structure can contain 1, 2 or 3 of those depending if you have been vaccinated or tested, or if you have recovered from the illness.
Python code
It's always about the details. So, I forked an existing git-repo and did some of my own tinkering. Results are at: https://github.com/HQJaTu/vacdec/tree/certificate-fetch
Original code by Mr. Hanno Böck could read QR-code and do some un-wrapping for it to reveal the payload. As I'm always interested in X.509, digital signatures and cryptography, I improved his code by incorporating the digital signature verification into it.
As CBOR/COSE was new for me, it took a while to get the thing working. In reality the most difficult part was to get my hands into the national public certificates to do some ECDSA signature verifying. It's really bizarre how that material is not made easily available.
Links:
- Swagger of DGC-gateway: https://eu-digital-green-certificates.github.io/dgc-gateway/
- This is just for display-purposes, this demo isn't connected to any of the national back-ends
- Sample data for testing verification: https://github.com/eu-digital-green-certificates/dgc-testdata
- All participating nations included
- QR-codes and raw-text ready-to-be-base45-decoded
- Payload JSON_schema: https://github.com/ehn-dcc-development/ehn-dcc-schema/
- Just to be clear, the payload is not JSON
- However, CBOR is effectively binary JSON
- List of all production signature certificates: https://dgcg.covidbevis.se/tp/
- Austrian back-end trust-list in JSON/CBOR: https://greencheck.gv.at/api/masterdata
- Swedish back-end trust-list in CBOR: https://dgcg.covidbevis.se/tp/trust-list
- The idea is for all national back-ends to contain everybody's signing certificate
Wallet
Mr. Philipp Trenz from Germany wrote a website to insert your QR-code into your Apple Wallet. Source is at https://github.com/philipptrenz/covidpass and the actual thing is at https://covidpass.eu/
Beautiful! Works perfectly.
Especially in Finland the government is having a vacation. After that they'll think about starting to make plans what to do next. Now thanks to Mr. Trenz every iOS user can have the COVID Certificate in their phones without government invovement.
Finally
Answers:
- Yes, duplication is possible, but not feasible in volume. You can get your hands into somebody else's certificate and can present a proof of vaccination, but verification will display the original name, not yours.
- Yes, there is even source code for creating the QR-code, so it's very easy to forge.
- Yes, the payload has a very strong elliptic curve signature in it. Any forged payloads won't verify.
Ultimately I was surprised how well designed the entire stack is. It's always nice to see my tax-money put into good use. I have nothing negative to say about the architecture or technologies used.
Bonus:
At very end of my project, I bumped into Mr. Mathias Panzenböck's code https://github.com/panzi/verify-ehc/. He has an excellent implementation of signature handling, much better than mine. Go check that out too.
