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fix description of MAC calculation (#1590)

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Hubert Chathi 2023-07-04 18:54:55 -04:00 • committed by GitHub
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changelogs/client_server/newsfragments/1590.clarification Normal file
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@ -0,0 +1 @@
Fix description of MAC calculation in SAS verification.

8
content/client-server-api/modules/end_to_end_encryption.md
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@ -776,7 +776,7 @@ The method used to calculate these MACs depends upon the value of the
message. All current implementations should use the `hkdf-hmac-sha256.v2` method which is
defined as follows:
The MAC used is HMAC as defined in [RFC
1. An HMAC key is generated using HKDF, as defined in [RFC
5869](https://tools.ietf.org/html/rfc5869), using SHA-256 as the hash
function. The shared secret is supplied as the input keying material. No salt
is used, and in the info parameter is the concatenation of:
@ -790,6 +790,10 @@ is used, and in the info parameter is the concatenation of:
- The Key ID of the key being MAC-ed, or the string `KEY_IDS` if the
item being MAC-ed is the list of key IDs.
2. A MAC is then generated using HMAC as defined in [RFC
2104](https://tools.ietf.org/html/rfc2104) with the key generated above and
using SHA-256 as the hash function.
If a key is being MACed, the MAC is performed on the public key as encoded
according to the [key algorithm](#key-algorithms). For example, for `ed25519`
keys, it is the unpadded base64-encoded key.
@ -801,7 +805,7 @@ form `{algorithm}:{keyId}`. For example, the key list could look like:
reconstruct the list from the names in the `mac` property of the
`m.key.verification.mac` message and ensure that no keys were added or removed.
The MAC values are base64-encoded and sent in a
3. The MAC values are base64-encoded and sent in a
[`m.key.verification.mac`](#mkeyverificationmac) message.
{{% boxes/note %}}