security: fix silent OT mal OT security

The malicious version of the silent OT protocol mistakenly used a
semi-honest OT protocol for the base OTs used in silent OT. This commit
changes it so that the security of the base OT protocol depends on
the chosen security of the silent OT protocol.

Author: robinhundt

cryprot-ot/src/extension.rs

@@ -47,7 +47,7 @@ pub const BASE_OT_COUNT: usize = 128;
 pub const DEFAULT_OT_BATCH_SIZE: usize = 2_usize.pow(16);
 
 /// OT extension sender generic over its [`Security`] level.
-pub struct OtExtensionSender<S: Security> {
+pub struct OtExtensionSender<S> {
     rng: StdRng,
     base_ot: SimplestOt,
     conn: Connection,
@@ -59,7 +59,7 @@ pub struct OtExtensionSender<S: Security> {
 }
 
 /// OT extension receiver generic over its [`Security`] level.
-pub struct OtExtensionReceiver<S: Security> {
+pub struct OtExtensionReceiver<S> {
     base_ot: SimplestOt,
     conn: Connection,
     base_rngs: Vec<[AesRng; 2]>,

cryprot-ot/src/silent_ot.rs

@@ -1,6 +1,6 @@
 //! Semi-honest and malicious Silent OT implementation using expand-convolute code [[RRT23](https://eprint.iacr.org/2023/882)].
 #![allow(non_snake_case)]
-use std::{io, marker::PhantomData, mem};
+use std::{io, mem};
 
 use bytemuck::cast_slice_mut;
 use cryprot_codes::ex_conv::{ExConvCode, ExConvCodeConfig};
@@ -34,9 +34,8 @@ pub type MaliciousSilentOtReceiver = SilentOtReceiver<MaliciousMarker>;
 
 pub struct SilentOtSender<S> {
     conn: Connection,
-    ot_sender: OtExtensionSender<SemiHonestMarker>,
+    ot_sender: OtExtensionSender<S>,
     rng: StdRng,
-    s: PhantomData<S>,
 }
 
 #[derive(Default, Debug, Copy, Clone, PartialEq, Eq)]
@@ -73,7 +72,6 @@ impl<S: Security> SilentOtSender<S> {
             conn,
             ot_sender,
             rng: StdRng::from_os_rng(),
-            s: PhantomData,
         }
     }
 
@@ -224,9 +222,8 @@ impl<S: Security> SilentOtSender<S> {
 
 pub struct SilentOtReceiver<S> {
     conn: Connection,
-    ot_receiver: OtExtensionReceiver<SemiHonestMarker>,
+    ot_receiver: OtExtensionReceiver<S>,
     rng: StdRng,
-    s: PhantomData<S>,
 }
 
 impl<S: Security> SilentOtReceiver<S> {
@@ -236,7 +233,6 @@ impl<S: Security> SilentOtReceiver<S> {
             conn,
             ot_receiver,
             rng: StdRng::from_os_rng(),
-            s: PhantomData,
         }
     }