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Clarifications around encoding of data within verification QR codes (#1839)

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Hugh Nimmo-Smith 2024-06-12 22:48:50 +01:00 • committed by GitHub
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changelogs/client_server/newsfragments/1839.clarification Normal file
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@ -0,0 +1 @@
Specify the encoding to be used when generating QR codes for device verification.

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content/client-server-api/modules/end_to_end_encryption.md
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@ -1179,10 +1179,16 @@ The process between Alice and Bob verifying each other would be:
###### QR code format
The QR codes to be displayed and scanned using this format will encode binary
strings in the general form:
The QR codes to be displayed and scanned MUST be
compatible with [ISO/IEC 18004:2015](https://www.iso.org/standard/62021.html) and
contain a single segment that uses the byte mode encoding.
- the ASCII string `MATRIX`
The error correction level can be chosen by the device displaying the QR code.
The binary segment MUST be of the following form:
- the string `MATRIX` encoded as one ASCII byte per character (i.e. `0x4D`,
`0x41`, `0x54`, `0x52`, `0x49`, `0x58`)
- one byte indicating the QR code version (must be `0x02`)
- one byte indicating the QR code verification mode. Should be one of the
following values:
@ -1194,23 +1200,23 @@ strings in the general form:
request event, encoded as:
- two bytes in network byte order (big-endian) indicating the length in
bytes of the ID as a UTF-8 string
- the ID as a UTF-8 string
- the ID encoded as a UTF-8 string
- the first key, as 32 bytes. The key to use depends on the mode field:
- if `0x00` or `0x01`, then the current user's own master cross-signing public key
- if `0x02`, then the current device's Ed25519 signing key
- the second key, as 32 bytes. The key to use depends on the mode field:
- if `0x00`, then what the device thinks the other user's master
cross-signing key is
cross-signing public key is
- if `0x01`, then what the device thinks the other device's Ed25519 signing
public key is
- if `0x02`, then what the device thinks the user's master cross-signing public
key is
- if `0x02`, then what the device thinks the user's master cross-signing key
is
- a random shared secret, as a byte string. It is suggested to use a secret
- a random shared secret, as a sequence of bytes. It is suggested to use a secret
that is about 8 bytes long. Note: as we do not share the length of the
secret, and it is not a fixed size, clients will just use the remainder of
binary string as the shared secret.
binary segment as the shared secret.
For example, if Alice displays a QR code encoding the following binary string:
For example, if Alice displays a QR code encoding the following binary data:
```
"MATRIX" |ver|mode| len | event ID