[Openid-specs-ab] JWE AES KeyWrap Example

Edmund Jay ejay at mgi1.com
Thu Sep 13 20:45:03 UTC 2012


Axel,

The keywrap algorithm takes n 64 bit blocks of plaintext and outputs (n+1) 64 
bit blocks of ciphertext.
In this case, the CMK is 128 bits which is 2x64 bit blocks (or 16 bytes) . The 
ciphertext is therefore 3 x 64 bit blocks or (24 bytes).
When unwrapped, the first 8 bytes of the decrypted text should be [a6, a6, a6, 
a6, a6, a6, a6, a6]. It's used as an integrity check.


Mike, 

I have the same results.

-- Edmund






________________________________
From: Axel Nennker <ignisvulpis at googlemail.com>
To: openid-connect-interop at googlegroups.com
Cc: Edmund Jay <ejay at mgi1.com>; Axel Nennker <Axel.Nennker at telekom.de>; Brian 
Campbell <bcampbell at pingidentity.com>; Emmanuel Raviart <emmanuel at raviart.com>; 
"openid-specs-ab at lists.openid.net" <openid-specs-ab at lists.openid.net>; Michael 
B. Jones <Michael.Jones at microsoft.com>
Sent: Thu, September 13, 2012 10:37:25 AM
Subject: Re: JWE AES KeyWrap Example

The length of Encrypted Key
[164, 255, 251, 1, 64, 200, 65, 200, 34, 197, 81, 143, 43, 211, 240, 38,
 191, 161, 181, 117, 119, 68, 44, 80]
is 24 bytes or 192 bits. Why?

Axel


2012/9/13 Mike Jones <Michael.Jones at microsoft.com>

Could one or more of you please check the attached AES KeyWrap example that I 
plan to add to the JWE spec?  It uses "alg":"A128KW" and "enc":"A128GCM".  Both 
algorithms produce repeatable results, and so the example should be fully 
reproducible.
> 
>Like the previous updated examples, the format of the JWE is:
>               
>header.encryptedKey.initializationVector.ciphertext.integrityValue
>and the Additional Associated Data value for the GCM calculation is computed 
as:
>               securedInput = encodedHeader + "." + encodedEncryptedKey + "." + 
>encodedInitializationVector;
> 
>                                                            Thanks,
>                                                            -- Mike
> 
> 
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