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Adding missing encodings for CleartextCredentials and CustomLabel #471

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Nov 21, 2024
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Adding missing encodings for CleartextCredentials and CustomLabel #471

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11 changes: 9 additions & 2 deletions draft-irtf-cfrg-opaque.md
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Original file line number Diff line number Diff line change
Expand Up @@ -697,7 +697,14 @@ def Store(randomized_password, server_public_key,
CreateCleartextCredentials(server_public_key, client_public_key,
server_identity, client_identity)
auth_tag =
MAC(auth_key, concat(envelope_nonce, cleartext_credentials))
MAC(auth_key, concat(
envelope_nonce,
server_public_key,
I2OSP(len(cleartext_credentials.server_identity), 2),
cleartext_credentials.server_identity,
I2OSP(len(cleartext_credentials.client_identity), 2),
cleartext_credentials.client_identity
))

envelope = Envelope {
envelope_nonce,
Expand Down Expand Up @@ -1586,7 +1593,7 @@ Expand-Label(Secret, Label, Context, Length) =
Expand(Secret, CustomLabel, Length)
~~~

Where CustomLabel is specified as:
Where CustomLabel is specified and encoded (following Section 3.4 of {{?RFC8446}}) as:
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A reference to RFC8446 might potentially be overkill here.

You might also specify CustomLabel as the concatenation of I2OSP(Length, 2), I2OSP(len("OPAQUE-" + Label), 2), "OPAQUE-", Label, I2OSP(len(Context)), and Context. This would also match how Preamble is specified in 6.4.2.1.

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Thanks! I contemplated doing it this way, but ultimately decided that referencing the section in RFC8446 was a more concise way to describe the concatenation. Hope that this is still clear enough.


~~~
struct {
Expand Down
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