Double blind $T$-private information retrieval (DB-TPIR) enables two users,
each of whom specifies an index ($\theta_1, \theta_2$, resp.), to efficiently
retrieve a message $W(\theta_1,\theta_2)$ labeled by the two indices, from a
set of $N$ servers that store all messages $W(k_1,k_2),
k_1\in\{1,2,\cdots,K_1\}, k_2\in\{1,2,\cdots,K_2\}$, such that the two users'
indices are kept private from any set of up to $T_1,T_2$ colluding servers,
respectively, as well as from each other. A DB-TPIR scheme based on
cross-subspace alignment is proposed in this paper, and shown to be
capacity-achieving in the asymptotic setting of large number of messages and
bounded latency. The scheme is then extended to $M$-way blind $X$-secure
$T$-private information retrieval (MB-XS-TPIR) with multiple ($M$) indices,
each belonging to a different user, arbitrary privacy levels for each index
($T_1, T_2,\cdots, T_M$), and arbitrary level of security ($X$) of data
storage, so that the message $W(\theta_1,\theta_2,\cdots, \theta_M)$ can be
efficiently retrieved while the stored data is held secure against collusion
among up to $X$ colluding servers, the $m^{th}$ user's index is private against
collusion among up to $T_m$ servers, and each user's index $\theta_m$ is
private from all other users. The general scheme relies on a tensor-product
based extension of cross-subspace alignment and retrieves
$1-(X+T_1+\cdots+T_M)/N$ bits of desired message per bit of download.