RE: JWK attributes for WebCrypto keys: last call

There is a group of individuals in the JOSE group that have strongly felt that 

 

1.       Usages of keys need to be restricted, although not necessarily as restricted as what the WebCrypto keys call for, thus the insistence for a single value in the field and

2.       If there if a proliferation of values for key usage is bad because it makes the code bases harder to work with.  This lead to the decision that ‘enc’ should be used both for key wrapping algorithms and content encryption algorithms.

 

On a purely personal level, I don’t necessarily agree with these decisions but they are what we have as the stated positions of the working group at the moment.

 

The real issue that I see is the question of having strings that allow for multiple different types of operations the can occur.  I could easily get behind the idea of registering “enc”, “enc-only”, “dec-only” as three strings that map to “encrypt+decrypt”, “encrypt”, “decrypt”.  Where I have a greater problem is when we get into the concept that we are going to allow for keys to do different things that might be bad for them.  Thus the ability to have a key usage of “wrapKey+encrypt” seems more problematic based on the fact that the algorithm is designed to either encrypt content or encrypt keys.  I am also not sure if you want to be able to make statements along the lines of “encrypt+decrypt+sign+verify” for an RSA public key.

 

Just as an attempt to get the set of issues clearly outlined, I think that this is where things fall:

 

1.       Should there be an ability to decompose the encrypt usage into its component items, and can the union need to be a new string rather than a combined string? (i.e. enc vs enc-only vs dec-only)

2.       Are there cases where there is a need to combine together different types of operations together in the use string (i.e. wrap + encrypt)  (I think that if the answer to this is no then we might not need the array which is going to get very strong pushback.)

3.       What is the level of importance of being able to restrict the usage of a key without knowing what the algorithm that the key is to be used with.  

 

Looking at the current text, the statement ‘enc’ is equivalent to ‘enconly, deconly,wrap,unwrap’ is incorrect.  The expectation is that the value of enc is to be interpreted based on the current algorithm value.  Thus it would be either ‘enconly,deconly’ or ‘wrap,unwrap’.

 

Jim