spiral-spir/src/lib.rs

pub mod client;
mod ot;
mod params;
pub mod server;
mod spiral_mt;

use aes::cipher::{BlockEncrypt, KeyInit};
use aes::Aes128Enc;
use aes::Block;
use std::mem;

use serde::{Deserialize, Serialize};

use std::os::raw::c_uchar;

use rayon::scope;
use rayon::ThreadPoolBuilder;

use serde_with::serde_as;

use spiral_rs::params::*;

use crate::ot::{otkey_init, xor16};
use crate::spiral_mt::*;

pub type DbEntry = u64;

// Encrypt a database of 2^r elements, where each element is a DbEntry,
// using the 2*r provided keys (r pairs of keys).  Also rotate the
// database by rot positions, and add the provided blinding factor to
// each element before encryption (the same blinding factor for all
// elements).  Each element is encrypted in AES counter mode, with the
// counter being the element number and the key computed as the XOR of r
// of the provided keys, one from each pair, according to the bits of
// the element number.  Outputs a byte vector containing the encrypted
// database.
fn db_encrypt(
    db: &[DbEntry],
    keys: &[[u8; 16]],
    r: usize,
    rot: usize,
    blind: DbEntry,
    num_threads: usize,
) -> Vec<u8> {
    let num_records: usize = 1 << r;
    let num_record_mask: usize = num_records - 1;
    let mut ret = vec![0; num_records * mem::size_of::<DbEntry>()];
    scope(|s| {
        let mut record_thread_start = 0usize;
        let records_per_thread_base = num_records / num_threads;
        let records_per_thread_extra = num_records % num_threads;
        let mut retslice = ret.as_mut_slice();
        for thr in 0..num_threads {
            let records_this_thread =
                records_per_thread_base + if thr < records_per_thread_extra { 1 } else { 0 };
            let record_thread_end = record_thread_start + records_this_thread;
            let (thread_ret, retslice_) =
                retslice.split_at_mut(records_this_thread * mem::size_of::<DbEntry>());
            retslice = retslice_;
            s.spawn(move |_| {
                let mut offset = 0usize;
                for j in record_thread_start..record_thread_end {
                    let rec = (j + rot) & num_record_mask;
                    let mut key = Block::from([0u8; 16]);
                    for i in 0..r {
                        let bit = if (j & (1 << i)) == 0 { 0 } else { 1 };
                        xor16(&mut key, &keys[2 * i + bit]);
                    }
                    let aes = Aes128Enc::new(&key);
                    let mut block = Block::from([0u8; 16]);
                    block[0..8].copy_from_slice(&j.to_le_bytes());
                    aes.encrypt_block(&mut block);
                    let aeskeystream = DbEntry::from_le_bytes(block[0..8].try_into().unwrap());
                    let encelem = (db[rec].wrapping_add(blind)) ^ aeskeystream;
                    thread_ret[offset..offset + mem::size_of::<DbEntry>()]
                        .copy_from_slice(&encelem.to_le_bytes());
                    offset += mem::size_of::<DbEntry>();
                }
            });
            record_thread_start = record_thread_end;
        }
    });
    ret
}

// Having received the key for element q with r parallel 1-out-of-2 OTs,
// and having received the encrypted element with (non-symmetric) PIR,
// use the key to decrypt the element.
fn dbentry_decrypt(key: &Block, q: usize, encelement: DbEntry) -> DbEntry {
    let aes = Aes128Enc::new(key);
    let mut block = Block::from([0u8; 16]);
    block[0..8].copy_from_slice(&q.to_le_bytes());
    aes.encrypt_block(&mut block);
    let aeskeystream = DbEntry::from_le_bytes(block[0..8].try_into().unwrap());
    encelement ^ aeskeystream
}

// Things that are only done once total, not once for each SPIR
pub fn init(num_threads: usize) {
    otkey_init();

    // Initialize the thread pool
    ThreadPoolBuilder::new()
        .num_threads(num_threads)
        .build_global()
        .unwrap();
}

pub fn print_params_summary(params: &Params) {
    let db_elem_size = params.item_size();
    let total_size = params.num_items() * db_elem_size;
    println!(
        "Using a {} x {} byte database ({} bytes total)",
        params.num_items(),
        db_elem_size,
        total_size
    );
}

// The message format for a single preprocess query
#[derive(Serialize, Deserialize)]
struct PreProcSingleMsg {
    ot_query: Vec<[u8; 32]>,
    spc_query: Vec<u8>,
}

// The message format for a single preprocess response
#[serde_as]
#[derive(Serialize, Deserialize)]
struct PreProcSingleRespMsg {
    #[serde_as(as = "Vec<[_; 64]>")]
    ot_resp: Vec<[u8; 64]>,
}

#[no_mangle]
pub extern "C" fn spir_init(num_threads: u32) {
    init(num_threads as usize);
}

#[repr(C)]
pub struct VecData {
    data: *const c_uchar,
    len: usize,
    cap: usize,
}

#[repr(C)]
pub struct VecMutData {
    data: *mut c_uchar,
    len: usize,
    cap: usize,
}

pub fn to_vecdata(v: Vec<u8>) -> VecData {
    let vecdata = VecData {
        data: v.as_ptr(),
        len: v.len(),
        cap: v.capacity(),
    };
    std::mem::forget(v);
    vecdata
}

#[no_mangle]
pub extern "C" fn spir_vecdata_free(vecdata: VecMutData) {
    unsafe { Vec::from_raw_parts(vecdata.data, vecdata.len, vecdata.cap) };
}