A look inside the European Covid Green Certificate - Rust Dublin

A look inside the
European Covid Green Certiﬁcate
Luciano Mammino ( )
@loige
loige.link/rust-green
22-02-2022 😱
1

Get these slides!
loige
2

👋I'm Luciano
Senior Architect @ fourTheorem (Dublin )
nodejsdp.link
📔Co-Author of Node.js Design Patterns 👉
Let's connect!
(blog)
(twitter)
(twitch)
(github)
loige.co
@loige
loige
lmammino
3

We are business focused
technologists that deliver.
| |
Accelerated Serverless AI as a Service Platform Modernisation
We are hiring: do you want to
?
work with
us
loige 4

loige
🦀I'm learning Rust as a hobby...
Live streaming my attempts to crack Advent of Code in Rust (with
and ): /
@gbinside @88_eugen Twitch YouTube
Wrote articles:
a few
How to to_string in Rust
Rust shenanigans: return type polymorphism
Where to go to learn Rust in 2021
Published (simple) crates: , , ,
a few jwtinfo allwords gmaps-static dgc
5

Disclaimers
loige
🤓I am not involved with the DGC working group

😢COVID has been tough on everyone,
we'll try to focus only on the tech here!
6

Agenda + Goals
loige
1. Needs and principles
2. 🗝Cryptographic model
3. 📦The data
4. 🧅Layers of encoding
5. 🛠Decoding in Rust
🤨Learn some cool technologies
🧐Learn a tiny bit of Rust
🤓Be nerdy and have fun!
7

The need for a digital
certiﬁcate in the COVID age
loige 8

The need for a digital
certiﬁcate in the COVID age
loige
😷We need a system to quickly provide a proof against COVID
(Vaccination, negative test, proof of recovery)
It needs to be personal, easy to carry around (digital),
easy to issue and to validate
🌎It needs to be secure against forgery and work across countries
9

The EU Covid Green Pass
a.k.a.
Electronic Health
Certiﬁcates (HCERT)

loige.link/hcert-spec
loige 10

Electronic Health Certiﬁcates (HCERT)
Requirements & Guiding Principles
loige
✍Signed data with machine readable
content
📃Use compact encoding
🤲Based on open standards
11

Asymmetric cryptographic signatures
loige
🤫 Private Key 📢 Public Key
🔗
101010101000101010010... 0101010101010101010101...
12

Asymmetric cryptographic signatures
loige
🤫 Private Key 📢 Public Key
101010101000101010010... 0101010101010101010101...
The owner of the
private key signs the
document
Anyone can validate the
signature using the
public key
13

What's inside a certiﬁcate?
loige
DGC container
Cryptographic header (Key Id,
Algorithm)
Cryptographic Signature
Header (Issuer, Issue date, expiry date)
14
Certiﬁcates list
vaccine, test, or recovery data
Personal data (name, surname, DoB)

An
example
loige loige.link/green-examples 15

{
"1": "DK",
"4": 1625054000,
"6": 1622462000,
"-260": {
"ver":"1.0.0",
"nam":{
"fn":"Klaus",
"fnt":"KLAUS",
"gn":"Jørgensen",
"gnt":"JOERGENSEN"
},
"dob":"1983-01-06",
"v":[
{
"tg":"840539006",
"vp":"1119349007",
"mp":"EU/1/20/1528",
"ma":"ORG-100030215",
"dn":2,
"sd":2,
"dt":"2021-05-03",
"co":"DK",
"is":"Danish Health Data Authority",
"ci":"URN:UVCI:01:DK:B986830007345F99AE898FB82C6C61F2#A"
}
]
}
}
An
example
loige loige.link/green-examples
Personal info
Vaccine info
DGC Header
16

Layered
encoding
loige
QRCODE ASCII mode
Preﬁx + Base45 encoding
Zlib compression
CWT signed data (COSE)
CBOR document
17
🧅

loige
HC1:NCFOXN%TSMAHN-H9QCGDSB5QPN9OO3:D4$X4-36
5KN-TMLV4.P7*ZOP-IMJTI94F/8X*G3M9JUPY0BZW4Z
*AK.GNNVR*G0C7PHBO335KN/NBEDBVBJ623323EAJ7U
J5PNDIB6PNS7B1DN%BBWC7WC7GB3683ML7SZ4ZI00T9
UKPSH9WC5PF6846A$Q 76QW6A/98T5WBI$E9$UPV3Q.
GUQ$9WC5R7ACB97C968ELZ5$DP6PP5IL*PP:+P*.1D9
R8Q02-DE%QHOJ+PB/VSQOL9DLKWCZ3EBKDYGIZ J$XI
4OIMEDTJCJKDLEDL9CZTAKBI/8D:8DKTDL+SQ05.$S6
ZC0JBY63-C3F+LBQ99Q9E$BDZIA9JJ-JS7BYZJ92KG0
TB9FNDA5KD9FED.B4JB3E9B9NNPCV9E6LFSD9C8J-QD
SWNG4C-TLNKE$JDVPLW1KD0KCZGBKQCJE%RH5WAMSSR
$F-75NXONQ84QV9/7/-LT1AIYBZGD$9RCLV-PTZ-K63
ET-D1757H3GF9MV2N7WNQSY1SBZT-:81JJLHFQ-VG$H
K00XWPD2
QRCode content "HC1:" (preﬁx)
Binary data encoded in
Base45
18

loige
Allows to encode binary data in text format (ASCII)
Like Base64, but it uses 45 characters instead:
loige.link/base45-explained
Base45
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Base45
loige
01001001 00100000 01100111
01101111 01110100 00100000
01101101 01111001 00100000
01110011 01101000 01101111
01110100 01110011 00100000
11011000 00111101
UTF8 (17 bytes)
I got my shots 💉
Hex (38 bytes)
49 20 67 6f 74 20 6d 79 20 73 68
6f 74 73 20 f0 9f 92 89
Base64 (28 bytes)
SSBnb3QgbXkgc2hvdHMg8J+SiQ==
Base45 (29 bytes)
0B9J3DSUEZ$DR4459DLWEH74Z7K23
Some binary data
21

loige
loige.link/base45-rfc
"A QR-code is used to encode text as a graphical image. [...] QR-
codes cannot be used to encode arbitrary binary data directly. [...]
Compared to already established Base64, Base32 and Base16
encoding schemes [...], the Base45 scheme described in this
document oﬀer a more compact QR-code encoding"
Base45
22

loige
Base45
NCFOXN%TSMAHN-H9QCGDSB5QPN9OO3:D4$X4-365KN-
TMLV4.P7*ZOP-IMJTI94F/8X*G3M9JUPY0BZW4Z*AK.
GNNVR*G0C7PHBO335KN/NBEDBVBJ623323EAJ7UJ5PN
DIB6PNS7B1DN%BBWC7WC7GB3683ML7SZ4ZI00T9UKPS
H9WC5PF6846A$Q 76QW6A/98T5WBI$E9$UPV3Q.GUQ$
9WC5R7ACB97C968ELZ5$DP6PP5IL*PP:+P*.1D9R8Q0
2-DE%QHOJ+PB/VSQOL9DLKWCZ3EBKDYGIZ J$XI4OIM
EDTJCJKDLEDL9CZTAKBI/8D:8DKTDL+SQ05.$S6ZC0J
BY63-C3F+LBQ99Q9E$BDZIA9JJ-JS7BYZJ92KG0TB9F
NDA5KD9FED.B4JB3E9B9NNPCV9E6LFSD9C8J-QDSWNG
4C-TLNKE$JDVPLW1KD0KCZGBKQCJE%RH5WAMSSR$F-7
5NXONQ84QV9/7/-LT1AIYBZGD$9RCLV-PTZ-K63ET-D
1757H3GF9MV2N7WNQSY1SBZT-:81JJLHFQ-VG$HK00X
WPD2
Base45
Decode
Compressed binary data
23

Zlib compression
loige
"zlib is designed to be a free, general-purpose, legally
unencumbered -- that is, not covered by any patents --
lossless data-compression library for use on virtually any
computer hardware and operating system"
zlib.net
25

Zlib compression
loige
Zlib inﬂate
Compressed binary data Decompressed binary data
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Zlib compression
loige
👀We start to see
some "readable"
information!
27

COSE / CWT
loige
CBOR Object Signing and Encryption / CBOR Web Token
28

CBOR !? 🤔
loige
But wait, what the heck is
✋
29

CBOR
loige
TLDR; Like JSON but in
binary!
loige.link/cbor-rfc
30

JSON
loige
A schema-less data format where a value can be:
Null
Boolean
Number
String
Array
Object
null
true
-17.34
"A programmer walks into a bar..."
["foo", 1.23, null, false, [22]]
{"foo": "bar", "manyvals": [1,2,3], "nested": {}}
31

CBOR
loige
A schema-less binary data format where a value can be:
Null
Boolean
Number
String Text
Array
Object Map
F6
F5
fbc031570a3d70a3d7
7820412070726f6772616d6d65722077616c6b7320696e746f2061206261722e2e2e
8563666f6ffb3ff3ae147ae147aef6f48116
a363666f6f63626172686d616e7976616c7383010203666e6573746564a0
32

CBOR
loige
It also supports:
Byte String (a sequence of raw bytes)
Tags (annotations that allow to create new types)
33

CBOR
loige
An example:
A3 63666F6F 63626172 686D616E7976616C73 83 01 02 03 666E6573746564 A0
{
"foo": "bar",
"manyvals": [
}
],
"nested": {}
1, 2, 3
34

COSE / CWT
loige
CBOR Object Signing and Encryption / CBOR Web Token
ok... again 😅
35

COSE
loige
loige.link/cose-rfc
CBOR Object Signing and Encryption
COSE (inspired by ) deﬁnes CBOR-based protocols for:
JOSE
Encrypted data
Cryptographic signed data
MACed data
36

CWT
loige
Like but for CBOR
JWT
loige.link/cwt-rfc
Deﬁnes a protocol for transferring claims between parties
CBOR Web Token
Claims are digitally signed for authenticity
37

CWT
loige
A CWT is made of 4 parts:
Protected header
CBOR Web Token
Non protected header
Payload
Signature
38

CWT
loige
A CWT is encoded as a (tagged) CBOR array with 4 values:
Protected header (binary string)
CBOR Web Token
Non protected header (map)
Payload (binary string)
Signature (binary string)
39

Protected
header
Binary String
loige
Array (length
4)
CWT tag
40
Unprotected
header
Map (length 0)
Payload
Binary String
Signature
Binary String

loige
CWT payload
{
"1": "DK",
"4": 1625054000,
"6": 1622462000,
"-260": {
"ver":"1.0.0",
"nam":{
"fn":"Klaus",
"fnt":"KLAUS",
"gn":"Jørgensen",
"gnt":"JOERGENSEN"
},
"dob":"1983-01-06",
"v":[
{
"tg":"840539006",
"vp":"1119349007",
"mp":"EU/1/20/1528",
"ma":"ORG-100030215",
"dn":2,
"sd":2,
"dt":"2021-05-03",
"co":"DK",
"is":"Danish Health Data Authority",
"ci":"URN:UVCI:01:DK:B986830007345F99AE898FB82C6C61F2#A"
}
]
}
}
Binary String follows (CBOR Encoded)
CBOR decode
(to JSON)
41

How to decode - quick recap
loige
1. Remove "HC1:" preﬁx
2. Base45 decode
3. Zlib decompress
4. Parse CWT
5. Parse CWT Payload as CBOR
6. Party hard! 🥳
Hey, let's implement
this...
in Rust!
42

loige
cargo new dgc-decode
Project bootstrap
43

// src/main.rs
fn main() {
let cert_data = "HC1:NCFOXN%TSMAHN-H9QCGDSB5QPN9OO3:D4$X4-365KN-TMLV4
todo!()
// 1. Remove "HC1:" prefix
// 2. Base45 decode
// 3. Zlib decompress
// 4. Parse CWT
// 5. Parse CWT Payload as CBOR
}
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// src/main.rs
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fn main() {
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todo!()
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// 2. Base45 decode
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// 4. Parse CWT
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}
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todo!()
// 2. Base45 decode
// 4. Parse CWT
// src/main.rs
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fn main() {
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}
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// src/main.rs
fn main() {
todo!()
// 2. Base45 decode
// 4. Parse CWT
}
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loige 44

fn main() {
let no_prefix = remove_prefix(cert_data);
todo!();
// 2. Base45 decode
// 4. Parse CWT
}
fn remove_prefix(data: &str) -> &str {
todo!()
// remove "HC1:" prefix and return remaining string
}
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fn main() {
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todo!();
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// 2. Base45 decode
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// 4. Parse CWT
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}
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todo!()
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}
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todo!()
}
fn main() {
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todo!();
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// 2. Base45 decode
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// 4. Parse CWT
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}
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fn main() {
todo!();
// 2. Base45 decode
// 4. Parse CWT
}
todo!()
}
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loige 45

fn main() {
todo!();
// 2. Base45 decode
// 4. Parse CWT
}
if data.len() < 4 || !data.starts_with("HC1:") {
panic!("Invalid prefix"); // IRL use a Result!
}
&data[4..]
}
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}
&data[4..]
fn main() {
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todo!();
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// 2. Base45 decode
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// 4. Parse CWT
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}
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}
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fn main() {
todo!();
// 2. Base45 decode
// 4. Parse CWT
}
}
&data[4..]
}
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loige 46

fn main() {
let decoded = decode_base45(no_prefix);
todo!()
// 4. Parse CWT
}
fn decode_base45(data: &str) -> Vec<u8> {
todo!()
// parse the string as base45 encoded and return the
// resulting raw bytes
}
// ...
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fn main() {
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todo!()
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// 4. Parse CWT
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}
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todo!()
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}
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// ...
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todo!()
}
fn main() {
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todo!()
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// 4. Parse CWT
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}
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// ...
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fn main() {
todo!()
// 4. Parse CWT
}
todo!()
}
// ...
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loige 47

loige
cargo add base45
# Cargo.toml
# ...
[dependencies]
base45 = "3.0.0"
48

fn main() {
todo!()
// 4. Parse CWT
}
base45::decode(data).unwrap() // IRL use a Result!
}
// ...
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fn main() {
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todo!()
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// 4. Parse CWT
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}
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}
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// ...
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fn main() {
todo!()
// 4. Parse CWT
}
}
// ...
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loige 49

fn main() {
let decompressed = decompress(decoded);
todo!()
// 4. Parse CWT
}
fn decompress(data: Vec<u8>) -> Vec<u8> {
todo!()
// decompress using zlib inflate
}
// ...
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fn main() {
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todo!()
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// 4. Parse CWT
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}
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todo!()
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}
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// ...
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todo!()
}
fn main() {
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todo!()
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// 4. Parse CWT
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}
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// ...
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fn main() {
todo!()
// 4. Parse CWT
}
todo!()
}
// ...
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loige 50

loige
cargo add inflate
# Cargo.toml
# ...
[dependencies]
base45 = "3.0.0"
inflate = "0.4.5"
51

fn main() {
todo!()
// 4. Parse CWT
}
inflate::inflate_bytes_zlib(data.as_slice()).unwrap()
// IRL use a Result!
}
// ...
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fn main() {
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todo!()
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// 4. Parse CWT
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}
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}
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// ...
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fn main() {
todo!()
// 4. Parse CWT
}
}
// ...
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loige 52

Are we on the right track?
loige
fn main() {
println!("{}", String::from_utf8_lossy(&decompressed));
}
// ...
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println!("{}", String::from_utf8_lossy(&decompressed));
fn main() {
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}
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// ...
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53

Are we on the right track?
loige
We are starting to see some
readable info! 🤩 54

fn main() {
let cwt_payload = get_cwt_payload(decompressed);
todo!()
}
fn get_cwt_payload(data: Vec<u8>) -> Vec<u8> {
todo!()
// Parse raw bytes as CBOR.
// Extract and return the raw bytes representing
// the CWT payload
}
// ...
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fn main() {
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todo!()
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}
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todo!()
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// the CWT payload
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}
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// ...
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todo!()
// the CWT payload
}
fn main() {
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todo!()
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}
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// ...
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fn main() {
todo!()
}
todo!()
// the CWT payload
}
// ...
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loige 55

loige
cargo add ciborium
# Cargo.toml
# ...
[dependencies]
base45 = "3.0.0"
ciborium = "0.2.0"
inflate = "0.4.5"
56

use ciborium::{de::from_reader, value::Value};
fn main() {
todo!()
}
let parsed: Value = from_reader(data.as_slice()).unwrap();
println!("{:?}", parsed);
todo!()
}
// ...
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fn main() {
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todo!()
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}
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todo!()
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}
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// ...
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fn main() {
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todo!()
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}
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todo!()
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}
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// ...
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loige 57

// ...
// IRL avoid .unwrap() like hell and propagate errors correctly!
let (tag, arr) = parsed.as_tag().unwrap();
assert_eq!(tag, 18);
let arr = arr.as_array().unwrap();
let payload = arr[2].as_bytes().unwrap();
payload.clone()
}
// ...
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// ...
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payload.clone()
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}
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// ...
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// ...
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payload.clone()
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}
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// ...
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// ...
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payload.clone()
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}
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// ...
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payload.clone()
// ...
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}
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// ...
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// ...
payload.clone()
}
// ...
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loige 59

fn main() {
let parsed_payload = parse_cwt_payload(cwt_payload);
}
fn parse_cwt_payload(data: Vec<u8>) -> Value {
// parse the binary data as CBOR
todo!()
}
// ...
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fn main() {
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}
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todo!()
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}
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// ...
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todo!()
}
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fn main() {
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}
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// ...
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loige 60

fn main() {
println!("{:#?}", parsed_payload);
}
from_reader(data.as_slice()).unwrap()
}
// ...
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fn main() {
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}
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}
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// ...
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fn main() {
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}
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}
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// ...
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fn main() {
}
}
// ...
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loige 61

Ok, let's make it more readable... 😅
loige
cargo add serde_json
63

use serde_json::to_string_pretty;
fn main() {
println!("{}", to_string_pretty(&parsed_payload).unwrap());
}
// ...
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fn main() {
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}
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// ...
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fn main() {
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}
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// ...
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fn main() {
}
// ...
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loige 64

All the code:
loige.link/green-code
loige 66

A better (& more complete) implementation
as a Rust library
loige
github.com/rust-italia/dgc
67

Exercise for the viewer:
Try to validate the signature
loige
🔑You can get the Public Key from the certificate
here: loige.link/green-examples
📑Here you can find more about how the
CoseSign1 protocol works: loige.link/cose-sign-
verif
📦You could use a crate like for crypto!
ring
(Spoiler: We implemented some of this stuff in the library!)
dgc
68

Is all this stuff legal? 😰
loige
👀You can certainly look into your certificate (and
the test certificates!)
🗣Looking into other people's certificate will
disclose a lot of privacy-sensitive info (thread
carefully)
📲Building a validator app? Check your country's
regulation (especially if you need to store data!)
69

Cover Picture by on
❤ Huge thanks to for some precius review sessions and many pull requests!
❤ Thanks to , , , , for reviews and suggestions.
FPVmat A Unsplash
rust-italia
@gbinside @88_eugen @AlleviTommaso @npmccallum @pelger
loige
☝nodejsdp.link
THANK YOU!
❤
70

A look inside the European Covid Green Certificate - Rust Dublin

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