[Openid-specs-ab] Core: is "dir" an allowed alg for Symmetric Encryption?

Brian Campbell bcampbell at pingidentity.com
Wed Dec 18 23:29:16 UTC 2013

Is "dir" an allowed alg for Symmetric Encryption? The text below from Core
10.2 kind of suggests it isn't. And doesn't provide a means of getting an
appropriately sized key for dir with A192CBC-HS384 or A256CBC-HS512. I
don't think this limitation was intended so wanted to raise the question.

Symmetric Encryption The symmetric encryption key is derived from the
client_secret value by using a left truncated SHA-256 hash of the octets of
the UTF-8 representation of the client_secret. The SHA-256 value MUST be
left truncated to the appropriate bit length for the AES key wrapping
algorithm used, for instance, to 128 bits for A128KW. If a key wrapping key
with greater than 256 bits is needed, a different method of deriving the
key from the client_secret would have to be defined by an extension.
Symmetric encryption MUST NOT be used by public (non-confidential) Clients
because of their inability to keep secrets.
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