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fix description of MAC calculation #1590

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merged 3 commits into from
Jul 4, 2023
Merged

fix description of MAC calculation #1590

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a248c89
fix description of MAC calculation
uhoreg Jun 27, 2023
5485179
add changelog
uhoreg Jun 27, 2023
f1bc8fa
put steps in a list
uhoreg Jul 4, 2023
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1 change: 1 addition & 0 deletions changelogs/client_server/newsfragments/1590.clarification
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@@ -0,0 +1 @@
Fix description of MAC calculation in SAS verification.
6 changes: 5 additions & 1 deletion content/client-server-api/modules/end_to_end_encryption.md
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Expand Up @@ -777,7 +777,7 @@ 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
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:
Expand All @@ -791,6 +791,10 @@ 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.

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.
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