Reading the whitepaper
I noticed it states :
Let A be an attestation. Suppose we wish to share this attestation with only identities X, Y and Z. We first generate a random symmetric key k, and encrypt A symmetrically. We denote this ciphertext sym(k, A).
Now we assume that X, Y and Z each have a public encryption key. Let asym(U,V,d) denote the asymmetric encryption between identities U and V of some data d. Specifically asym(U,V,d) = sym(DH(U,V),d)
Where DH(U,V) is a symmetric key generated from the public key of U and the private key of V using a Diffie-Hellman key exchange.
Create a random and ephemeral public/private key pair R, and create the data blob made up of ( sym(k,A), asym(X,R,k), asym(Y,R,k), asym(Z,R,k) )
Why is A encrypted symmetrically?
Reading the Security.SE questions “Why is symmetric encryption still used? [duplicate]” and “Asymmetric vs Symmetric Encryption” a potential reason for using symmetric encryption is speed but I don't see the context reasoning for using it in this specific case?